EUROPEAN ORGANISATION
FOR THE SAFETY OF AIR NAVIGATION
EUROCONTROL
STFTV
Propositions for a
Transponder Verification
Strategy
Report presented to the SURT meeting in May 1995
EEC note nº 20 / 95
Approved for publication
by the Head of Division B2
Issued : September 1995
Ce rapport n' est pas un document contractuel.
Les informations contenues ne représentent pas
nécessairement la politique officielle de l'Agence. / This report cannot be treated as a contractual
document.
The views expressed herein do not necessarily reflect the official views or policy of the Agency.
For any information on this document, please contact :
Michel BIOT
C.o.E. COM
FAX : int - 33 1 - 69 88 73 33
Centre Expérimental EUROCONTROL
B.P. 15
F - 91222 BRETIGNY sur ORGE CEDEX
FRANCE
REPORT DOCUMENTATION PAGE
Reference :
Security Classification :
EEC Report Nº 20/95
Unclassified
Originator :
Originator (Corporate Author) Name/Location :
EEC - Division B2
EUROCONTROL Experimental Centre
B.P.15
F - 91222 Brétigny sur Orge CEDEX
FRANCE
Telephone : 33 (1 ) 69 88 75 00
Sponsor :
Sponsor (Contract Authority) Name/Location :
EUROCONTROL EATCHIP
Development Directorate
EUROCONTROL Agency
Rue de la Fusée, 96
B-1130 BRUXELLES
BELGIUM
Telephone : 32 2 729 90 11
EATCHIP Surveillance Team
Title:
PROPOSITION FOR A TRANSPONDER VERIFICATION STRATEGY
Author
Date
Pages
Figures
Annexes
References
Michel BIOT
09 / 1995
37
( in text )
15
-
EATCHIP
Task Specification
SUR ET 1 ST04
EEC Task Nº
Task No. Sponsor
Period
AT 67
RS 5
1994 - 1995
Distribution Statement :
(a) Controlled by
(b) Special Limitations
(c) Copy to NTIS
:
:
:
Descriptors (keywords) :
Abstract
Heads of division B2 and DED3
None
NO
Transponders , Maintenance
:
This note describes propositions for a global approach to verify transponders respect the high level
of quality that is required in the new radar environment.
It addresses both periodic inspection and on-line alert.
STFTV
Propositions for a
TRANSPONDER
VERIFICATION
STRATEGY
EUROCONTROL
PREL IM INARIES
The Surveillance Team ( SURT) of EATCHIP created in 1994 a Task Force called STFTV ( for Surveillance Task
Force on Transponder Verification ) in order to establish a strategy for the verification of transponder replies.
In this respect, this Group has held 4 main meetings, executed some trials concerning transponder anomalies in a
real radar environment, collected information concerning transponder population and maintenance requirements in
the ECAC States, developed an automated process on present transponder test sets, started considering the use of
tools either existing or under development, for producing an alert device in ATC centres.
In the line of his task, the Group has assembled data and proposals for a Global system for the Surveillance of
transponders. It contains propositions and queries concerning the maintenance of present transponders, the
development of an alert device, and some considerations for the future generation of transponders.
The STFTV REPORT that follows has been presented by the Task Force leader to the Surveillance Team during
its May 1995 meeting; comments are now expected from the ECAC Aeronautical Administrations they represent, in
order to go ahead in developing the proposed strategy.
Task Force Participants
Andreas
SENGSTSCHMID
AUSTROCONTROL
[A]
Danny
DE VOS
RVA - RLW / CANC
[B]
Wolfgang OSENBRüGGE
DFS
/ SNO 2
[D]
Gilles
RAT
STNA
/ 4SA
[F]
Gérard
BESOMBES
STNA
/ 4SS
[F]
Michel
GUETTIER
STNA
/ 4SM
[F]
Bruno
RABILLER
STNA
/ 2RC
[F]
Joanna
BATES
CAA
/ ATS.SD
Pierre
RUAULT
EUROCONTROL / DED3
[ HQ ]
Pierre
KERSTENS (part-time)
EUROCONTROL / DED3
[ HQ ]
Tony
HAYES
EUROCONTROL / DEI 2
[ HQ ]
Task Force Leader and Report Author :
(part-time)
Michel BIOT
EUROCONTROL
• STFTV •
[
[ UK ]
EUROCONTROL / B 2 [ EEC ]
Final Report to SURT ][ May 1995 ]
page 1
--
-- SUMMARY --
--
INT RODUCT ION : NECESSIT Y T O INCREASE
T HE T RANSPONDER'S QUAL IT Y L EVEL
It is not necessary to recall here the importance of the SSR data in global ATC tasks.
The SSR system consists of both ground and airborne equipment, but whereas the ground part presents no
difficulty in being verified almost permanently, the present reliability of the airborne part is far from 100 %.
The evolution of ATC during recent years, as well as in the planned near future, placed the transponder on a higher
level of importance. Indeed, for various reasons, it has become a KEY element in air traffic control:
①
Already non existent in some areas, primary radar is going to disappear above the continental
area of most ECAC countries; therefore NO SAFETY NET exists anymore at the ground
stations, should the transponder's replies be missing or wrongly interpreted. ATC cannot accept
anymore replies too often missing or so corrupted that they would not pass the first stages of the
SSR extractor.
➁
The INCREASING TRAFFIC in many control sectors need to make use of sophisticated
algorithms, themselves needing a higher probability of acceptable replies and plots.
➂
the efforts to reduce the AIRCRAFT SEPARATION (longitudinal and lateral), for both traffic
potential and flight time management also require more accurate reply signals.
➃
The same is requested for an efficient and SAFE TCAS.
⑤
The amount of money spent on new MONOPULSE GROUND STATIONS must be accompanied
by a corresponding effort on the transponder side: these sensors require also more accurate
replies , because they work with a reduced number of replies ( objective : less than 3 per mode, A
& C ) and smaller pulse position acceptance windows ( in any case in excess of the ICAO
tolerance).
The AIC document reproduced in ANNEX 1 , addressed to the Administrations and the Aircraft Operators explicitly
developed these themes a certain time ago.
In short :
For SAFETY reasons,
☞
the reply probability of the transponder must be closer to 100 %;
For TRAFFIC development,
for use of the ATC SYSTEMS now and later being installed,
☞
⇒
the quality of the reply signal must be such that no decoded data is corrupted.
To reach this goal, a solution - in the form of a verification procedure - must be now installed to make
sure the transponders ( their replies) respect the high quality that is needed.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 2
REPORT SUM M ARY
The paragraphs and divisions correspond exactly with those in the MAIN REPORT.
In the text, the term transponder is often abbreviated into " XPDR " ; other abbreviations are listed page 9.
1
Pr e s e nt s itua tion
The history of transponders problems shows a reduction of out-of-norm units from 15 to 3 % over the last
10 years ( proportion is double for General Aviation ); present Mode S units are still better, but the higher
accuracy now requested reduces the improvement and besides, it appears in the new radar stations that
these new Mode S transponders sometimes present unexpected faults, in software as well as in hardware.
Recent trials with MONOPULSE radar showed that the percentage of correct codes may decrease to 50 %
if one characteristic is out-of-norm, to 0 % if one is out and another is just at the tolerance limit.
2
Ev olution of the pr oble m
2.1
SHORT TERM : in order not to lose any aircraft plot, the old radar stations were not adapted to the ICAO
limits but included much larger "windows" accepting the numerous out-of-norm pulses.
For many reasons, this era is finished. So, already now, the transponder replies must be more accurate,
with reply percentage closer to 100.
2.2
COEXISTENCE : it was planned to equip all aircraft flying IFR & VFR with Mode S transponders for 1998
or 1999. The reality will be nearer to 50 %. So, old transponders will remain in service for some years in the
ATC monopulse environment. This problem will have to be managed efficiently and safely.
A recent inquiry showed that the transponder's population end of 1994 is distributed as follows:
92 % old Cavity Transponders ( Mode A or A•C ) --- 4 % RECENT Mode A•C --- 4 % Mode S.
2.3
FUTURE SITUATION:
when effectively all transponders will be of Mode S type, the problem of their
verification could be solved efficiently using their B.I.T.E. possibilities. Normalisation process is needed
relatively soon, in such a way that some of the B.I.T.E. functions will be oriented towards the ATC needs
(the detection of some characteristics and their relevant communication to the ground).
3
Pos s ible a ppr oa c he s for TR A N SPON D ER v e r ific a tion
3.1
PREREQUISITES
• the transponder must respect the norm;
• the maintenance standards must be adapted to the new radar environment;
• an on-line alert device to supplement the improved maintenance in case of sudden unexpected failures ;
• this common solution must be rapidly installed to retain safety with all the old transponders still in the air;
• the transponder should be reconsidered at an adequate higher level by ICAO.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 3
3.2
CONSEQUENCES: the transponder verification procedures in the above defined radar environment imply
the following decisions to be taken:
☞ ① improved regular maintenance
☞ rapid implementation of these 2 decisions
☞ ➁ on-line alert device
☞ official SURT request to JAA and ICAO.
3.3, 3.4 VERIFICATION: having listed the possibilities of XPDR verification tools the group did NOT retain
☞
☞
☞
the DATAS - like equipment ( too difficult to install, too costly, many aircraft not covered);
the DATAS - like equipment at companies hangars (only easier to install than above);
the GTVS project (looks fine, but installed all over Europe it is heavy, costly, not adapted to
future Mode S extensions and too late for all the old transponders).
( DATAS : EUROCONTROL's Data link and transponder Mobile Measurement System)
( GTVS : Proposed automatic Ground Transponder Verification System )
3.5
SEPARATION BETWEEN THE XPDR TYPES:
it appears that any solution to the problem must include
some differences of treatment between the different types of transponders categorised as follows:
OLD MODE A•C
/
RECENT MODE A•C
4
A c tion on the m a inte na nc e
4.1
SCHEDULED MAINTENANCE : its aim is:
4.2
/
PRESENT MODE S
/
FUTURE MODE S
+++ to guarantee, as far as possible,
+++ that the equipment will run correctly,
+++ within the requested tolerance limits,
+++ up to the next test passage.
MAINTENANCE REQUIREMENTS:
mainly based on the FAA's requirement, many countries impose
additions, bench obligations, various periodicity ( sometimes depending on the transponder type ), various
test sets (but mostly from one well known manufacturer); seldom reduced to manufacturer's technical
choice.
4.3
ON CONDITION :
often used exception to the common regulations, it is based on an agreement between
the transponder manufacturer, the aircraft assembler and the administration. It made the solution of the
transponder verification difficult to compare.
4.4
RAMP TEST SETS : most present units measure the characteristics listed in FAR 43, plus very few other
ones; they are also limited in accuracy (or readability).
4.5
TEST SET AUTOMATION :
EEC trials on existing ramp & bench test sets showed that it is possible to
automate existing test sets but the manufacturers should be interested in retrofitting. Otherwise, this could
be the base of future contracts.
4.6
POSSIBLE RESTRAINTS : the harmonisation and improvement could suffer from the variety of repair
habits, the not-resetting to nominal values, the presence of very old transponders or the financial capacities
of the workshops.
4.7
POSSIBLE IMPROVEMENTS : based on an ECAC harmonisation around the best rules, they apply to
periodicity and range of tests, specific treatment for old transponders, bench tests additions, reset-tonominal procedure, automation of test sets, new bench & ramp test sets and inspection of workshops.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 4
4.8
PROPOSITIONS :
A National Maintenance regulations for transponders identical in all ECAC States.
1 To use the existing FAR43 measurements complemented by the F1⇒ F2 spacing measurement
and the Mode A•C acceptance vs. P1 ⇒ P3 spacing verification, for Ramp Testing
( it is yet possible ).
2 To set up a periodicity of
1 year for Ramp Test,
2 years for Bench Test.
3 To request a yearly Bench Test for all aircraft and transponders older than 12 years .
During this operation, more characteristics should be controlled.
4 By each passage on the bench, whatever the reason and the periodicity, the characteristics
would be restored to the nominal values.
B Other Requests
5 To establish national procedures that allows EUROCONTROL to get access to measurement
records of the transponders brought to workshop.
6 To insure that workshops are inspected on a sufficiently frequent basis.
7 To encourage the European transponder manufacturers to produce low cost Mode S LEVEL 2
transponders, replacing the existing Mode A•C units for the bulk of General Aviation.
4.9
OBJECTIONS : some objections to the extension of the maintenance regulations have already been made;
corresponding replies justify the propositions of the Task Force.
5
A le r t de v ic e s
5.1
REASON : An alert device must be installed (see § 3.1 & 3.2 ) to complete the Improved Maintenance; it
is essentially a SAFETY NET, for both suddenly failing transponders and those coming from countries
where ECAC ( or FAA ) rules do not apply.
5.2
TECHNIQUE :
The alert should be based on sudden changes in transponder replies received by the
radar ground equipment. Some manually observed faults have been and are still reported. Failures must
be detected, only important ones being presented to the ATC controller; but all should get an efficient
follow-up. Three ways are proposed thereunder; and none of them need external equipment.
5.3
DETECTION BY RDPS : By principle as by construction, the Radar Data Processing System tries to be
insensitive to " bad " replies; so at a first glance, it looks not a good way; but it could be run through a
special treatment chain in parallel to the main one(s), working from the start on “clean” video. Use of
special algorithms and other acceptance windows as well as the assembling of such chains in multiradar
are part of the idea.
5.4
RASS-S TOOL :
This tool presently under consideration for the Monitoring of the Radar Sensors could
be extended towards the analysis and recording of some XPDRs characteristics; in any case this tool
needs to distinguish between radar and/or XPDR faulty behaviour and so to analyse some XPDR replies.
Limitations lie in the amount of data than can be either recorded or the amount of characteristics than can
be controlled.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 5
5.5
PASSIVE GTVS :
When a feasibility study was made in 1993/94, a low cost variant was proposed only
capable of passive testing; it analyses passively the transponder’s replies through an equipment derived
from the Polar Data Processor now used to control various radar sensors. It seems that the number of
measurable characteristics is larger than in the 2 above solutions.
5.6
FOLLOW-UP :
The alarm should be presented to the ATC controller only in case of important failure
affecting the control. For minor faults, it should alert the maintenance services only. But in any case, both
the pilot and the maintenance services should be informed of a failure via a procedure established by
operational staff and maintenance specialists.
5.7
PROPOSITION :
The Group proposes to examine the 3 opened ways for Alert as defined.
• The implementation will need study & development phases, followed by a retrofit of existing installations.
• The problem lies in the time scale. To shorten the duration of these studies, the Group proposes to
launch feasibility contracts; to gain the largest benefit, they should be addressed to the manufacturers
already working in these domains (e.g. radar development manufacturers for the RDPS).
• Further, it is not impossible that a fourth approach could be found by COMBINING ideas from the three
described.
6
B ITE Pos s ibilitie s
6.1
THE BITE : it is a sub-element of any equipment developed to record and possibly analyse some of its
functions or status. In present Mode S transponders, it is not yet usable for ATC purposes; with increased
capacity and particularly devoted to our ATC needs, it could in the long term be used as a more complete
alert device. But it applies only to the future generation of Mode S transponders.
6.2
CENTRAL MAINTENANCE. SYSTEM : short description of how the BITE installed in many units aboard
the aircraft can be managed to serve the maintenance services, on-line and off-line ( after landing
generally).
6.3 , 6.4 USE IN ATC SURVEILLANCE : the BITE included in future transponders should be used to inform online both ATC, pilot and maintenance services of any malfunction, transmitted to the ground through either
the Mode S messages themselves or, if not possible, any other communication channel; but, in any case,
automatically. The Mode S procedures should be adapted in this respect.
6.5
PROPOSITIONS:
• To study the possibility, for new equipment, of using an extended B.I.T.E., measuring the
parameters that are important to the ATC, in Mode A•C & Mode S functions.
This could be executed through a contract placed with a common group of European
equipment manufacturers and aircraft assemblers.
•
To add these BITE - issued data to the list of messages transmitted to the ground;
first through the DATA LINK channel of the Mode S,
possibly later through any other air-ground communication channel.
It is a long term action; ECAC community should urge the manufacturers to include this extended BITE in
their equipment; with the aim of making it mandatory in the middle term.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 6
7
C onc lus ions
As a conclusion of the report, it is proposed:
1
To adopt the Improved Transponder Maintenance procedure defined in paragraph 4.8
[ § 4.8 propositions 1 to 4 ].
2
To assemble more data concerning transponders tested on the bench, whatever the reason
for removal, including the Mode S faults; the EEC would be the focal point of this collection.
[ § 4.8 proposition 5 ].
3
To introduce discussions at the JAA level, to see how the transponder can be reclassified at the
adequate level. Presently, there are no maintenance regulations installation certificatio only exists.
Discussions should start with the JAA administration to reach a common understanding about
transponders maintenance workshops.
[ § 4.8 proposition 6 ].
A member of the Group should be officially mandated by the SURT to JAA authorities.
The SURT should also find a way to encourage European manufacturers to produce low cost
Mode S level 2 transponders.
[ § 4.8 proposition 7 ].
4
To engage the alert concept developments, through the 3 ways (RDPS, RASS-S &
PASSIVE GTVS ), providing the SURT would approve this. At the end of this study phase,
a choice should be made, possibly mixing the 3 approaches.
[ see chapter 5 ].
5
To collect more information about the B.I.T.E. functions, in present transponders and those in
development.
Having difficulties to receive replies from the manufacturers concerned in the absence of
commercial interest and / or fear of communicating information to competitors , the Group
should be assisted by the SURT in this task.
[ see chapter 6 ].
6
To complete the evaluation of RAMP & BENCH TEST SETS automation and to engage a
BENCH TEST SET policy to assure the fulfilment of procedures defined by the group and
to promote the appropriate tool; this includes the BENCH UNITS needed by the Administrations.
[ see § 4.5 ].
Future tasks include assessing the influence of Mode S electrical faults, their occurrence and their effect on the
TCAS system.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 7
T ABL E OF CONT ENT S
-
Preliminaries
1
SUMMARY
-
Introduction
2
-
Report summary
3
-
Table of Contents
8
-
List of Annexes and Abbreviations
9
MAIN REPORT
1
Present Situation
1.1
1.2
1.3
2
Evolution of the Problems
2.1
2.2
2.3
3
6
29
Reason ............................................................................................... 29
Technique .......................................................................................... 29
Detection by RDPS ............................................................................ 29
Use of the RASS - S tool .................................................................. 32
Use of Passive GTVS ........................................................................ 32
Follow-up ............................................................................................ 33
Proposition ......................................................................................... 33
BITE Possibilities
6.1
6.2
6.3
6.4
6.5
7
21
Regular maintenance ......................................................................... 21
Maintenance requirements and harmonisation .................................. 21
On Condition procedures ................................................................... 22
Presently used ramp test equipment .................................................. 22
Test Equipment Automation ............................................................... 23
Possible restraints .............................................................................. 25
List of possible improvements ............................................................ 25
Propositions........................................................................................ 26
Justifications....................................................................................... 27
Alert Devices
5.1
5.2
5.3
5.4
5.5
5.6
5.7
17
Prerequisites ...................................................................................... 17
Consequences ................................................................................... 17
Verification possibilities ...................................................................... 18
Methods NOT retained by the Group ................................................. 18
Separation between the various types of XPDRs .............................. 20
Action on the Maintenance
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5
15
Short term........................................................................................... 15
Coexistence of various generations of transponders ......................... 15
Future situation .................................................................................. 16
Possible Approaches for Transponder Verification
3.1
3.2
3.3
3.4
3.5
4
10
History of transponder problems ........................................................ 10
Consequences of out-of-norm characteristics .................................... 11
Transponder population ..................................................................... 14
34
This proposition is for the long term ................................................... 34
Basic principles of Central Maintenance System - CMS .................... 34
For the purpose of ATC surveillance .................................................. 35
Transmission ...................................................................................... 35
Proposition ......................................................................................... 36
Conclusions
37
ANNEXES
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 8
L IST OF ANNEXES
ANNEX 1
EUROCONTROL AIC nº 3 ( 20 Aug. 1992 )
ANNEX 2
Occurrence of Out-of-norm Characteristics
ANNEX 3
STNA Records of XPDRS returned to Maintenance
ANNEX 4
STNA Notice to Airlines ( 1993 )
ANNEX 5
Influence of Out-of-norm Characteristics on Radar Data:
a] Jan.uary 1995 : STNA - EEC -THOMSON SDC
ANNEX 6
Influence of Out-of-norm Characteristics on Radar Data:
b] January 1995 : RVA Brussels Airport
ANNEX 7
Influence of Out-of-norm Characteristics on Radar Data:
c] March 1995 :
DFS at GöTZENHAIN
ANNEX 8
Influence of Out-of-norm Characteristics on Radar Data: Combined Results
ANNEX 9
Transponder Proportions in the ECAC Countries
ANNEX 10
Maintenance Requirements in each Country
ANNEX 11
List of Parameters and Test set Possibilities
ANNEX 12
IFR Test set Automation
ANNEX 13
Detection of Out-of-norm transponders by the SSR (incl. Multi - Radar )
ANNEX 14
Working Paper on an Initial RASS RTQMS ( Real Time Quality Monitoring System )
ANNEX 15
Present BITE in Airborne Equipment
L IST OF ABBREVIAT IONS
ADLP
Airborne Data Link Processor
BITE
Built- In Test Equipment ( here, in transponders)
DATAS
Data Link Test and Analysis System
GA
General Aviation
GTVS
Ground Transponder Verification System
JAA
European Joint Aviation Authorities
MCDU
Multipurpose Control and Display Unit
MTBF
Mean Time Between Failure
MTPA
Mobile Transponder Performance Analyser
RASS
Radar Analysis Support System
RDPS
Radar Data Processing System
STNA
Service Technique de la Navigation Aérienne ( F )
TCAS
Traffic alert and Collision Avoidance System
XPDR
Transponder
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 9
-1
-- MAIN REPORT --
--
PRESENT SIT UAT ION
1 .1
H is tor y of tr a ns ponde r pr oble m s
+++
Various analysis including principally the EUROCONTROL's MTPA and DATAS campaigns did show an
evolution in the respect of the ICAO norms, with percentage figures decreasing from
◆
15 % out-of-norm, 10 years ago, down to 3 % in 1993, for commercial aircraft;
◆
wice these figures by general aviation.
As an example, for an middle class airport with 150 departures of different aircraft, daily 5 aircraft take off
with out-of-norm XPDRs ( if one counts the two XPDRs installed, this figure is probably higher).
+++
Recent reports of transponders returned to maintenance workshops in France did show similar results: for
the Commercial aviation, 1 every 5 transponders returned for scheduled maintenance has exceeded the
ICAO norm three years after its previous passage on the bench. And the situation is worse for General
aviation or Business aircraft.
These last data play in favour of a shorter maintenance periodicity.
See ANNEXES 2 & 3.
+++
The decrease of faulty units percentage is partly due to the pressure exercised by some national
administrations on the aircraft operators (sometimes as a results of the measurement campaigns); it
follows the development of new technologies in electronic equipment (analogue ⇒ digital, cavity ⇒ solid
state frequency sources, etc....); the installation of the Mode S was an additional incentive to develop these
new technologies.
This evolution of transponder quality is encouraging, but
◆
the demand for transponders whose characteristics are nearer to the nominal values partly reduces
the effect of the improvement ( this is requested by monopulse radar);
◆
most of the General Aviation is still equipped with “ classic “ XPDRs, that-is-to-say Mode A•C units
(sometimes even without Mode C capability); and these XPDRs evidently present the largest amount of
failures or misalignment, hence creating the bulk of the present problems.
One should not conclude that the other types are perfect! They show far less shift in their characteristics
but
new problems will appear in Mode S transponders because of their increased complexity, especially in the
software domain. Especially, but not exclusively : a recent Mode S XPDR was found replying with some
pulses at 200 ns from the normal position. A wrong address is not infrequent too.
A notice to Aircraft Operators shown in ANNEX 4 insists on the necessity to respect the Mode S part of
airborne equipment as much as the classic " electrical " characteristics.
+++
Some other strange situations also appear at the extractor input, in the Mode S environment: isolated
pulses; other having for x antenna turns, exactly twice the normal width, all at the right PRF; Mode A/C
replies with different pulse widths.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 10
1 .2
C ons e que nc e s of out-of-nor m c ha r a c te r is tic s
The effect of characteristics deviating from the nominal values and exceeding the tolerated ICAO limits
were known but not yet well measured up to now.
A very limited correlation between out-of-norm transponders and the resulting radar pictures was tried in
1988 during an MTPA campaign; but the possibility to observe something interesting was reduced because
the radar system was HIGHLY FAILURE TOLERANT.
This was also the reason why few out-of-norm XPDRs generated, up to now, problems in the ATC. But this
situation is changing. See further down.
To acquire knowledge in this area, the Group initiated recently some trials at a few accessible radar
stations:
1.2.1
October 1994 : STNA - EEC
An EEC transponder has been modified : one pulse is moved around its nominal position and / or its width
is modified. The other characteristics remain nominal. Consequently, the Mode A information may be
wrongly decoded, the presence of the reply being always detected because the F1 & F2 pulses remain
correctly placed.
Situated on a fixed position, on top of the EEC building, it is seen by the Orly ground station.
The resulting percentage of correct code is :
one characteristic out of norm, exceeding the ICAO limit by 100 ns :
.
54 %
.
17 %
two characteristics are modified
a] the two situated just at the limit
.
.
b] one just at limit, the other exceeded by 100 ns .
.
c] between these two
.
.
.
.
.
0%
% between 0 and 17
These first results are repeated in the next trials, in a more complete form; in the present tests, the pulse
shape and position are observed at the output of the XPDR; a distortion may occur because of the very low
altitude above ground of the XPDRs antenna. So, the above figures are not very reliable, hence the
brackets( ).
1.2.2
January 1995 : STNA - EEC - Thomson SDE
The same EEC transponder has been modified and installed on the same place; but this time the video is
measured with a digital oscilloscope at the output of the interrogator receiver;
same tests :
1 ] C1 modification, in width and position
additions :
2 ] modified F1 & F2 pulse widths, simultaneously varying the F1 ⇒ F2 spacing,
3 ] modified F1 width and position vs. the whole of the reply,
4 ] modified XPDR reply frequency.
◆ F1 ⇒ F2
The detection depending on the F1 & F2 characteristics, the modification of these values
generate a reduction of reply detection in the case two parameters lie at the limit of the ICAO norm or just
beyond. But the present extractor is mostly sensitive to narrow pulses; the ERM can bear a wide range of
F1 & F2 widths and spacing values because several extraction criteria are used (edge to edge, edge to
state coincidence ). And with these criteria the plot detection recovers a high %, when both F1 and F2 have
the same widths. Which is not the case when only F1 is too narrow ( < 300 ns ), whatever its spacing
compared to the rest of the reply.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 11
◆ One pulse
When one code pulse only is modified (here, pulse C1) in width & position, the plot
detection is of coarse not affected, depending only on the framing pair, the resulting % of correct code is
better than the ones obtained in the § 1.2.1 (because of what is written above about pulse video
measurement). The extractor is more sensitive to lower end limits ( narrow pulses).
◆ Frequency test
The replies detected and the plots extracted both accept ( 100 % ) wide variation of
XPDR reply frequency ( 1090 ± 7 MHz ! ) because the receiver's bandwidth is large enough.
⇒
This radar is rather tolerant to large fluctuations of the XPDR parameters, quite beyond the ICAO
limits. The tests confirm that the more efficient an extractor is regarding degarbling, the less tolerant it
is with out-of-norm parameters.
The tests also showed that it is very difficult to forecast the behaviour of the radar when more
than two parameters are not nominal. Some transponders may show complex alterations; ιt is not
possible to test all configurations.
See the complete report in ANNEX 5.
1.2.3
January 1995 : RVA Brussels Airport
The modified EEC transponder has been installed in the surroundings of the new CANAC radar station,
where two RECENT MONOPULSE RADARS of different manufacturers are installed ( 400 m from each
other).
The same EEC transponder has been installed on top of the control tower ( 1 NM from the radars), with its
reply delay artificially increased in order to appear virtually at 40 NM range.
The tests are the same as above :
1 ] C1 modification, in width and position
2 ] modified F1 & F2 pulse width, simultaneously varying the F1 ⇒ F2 spacing,
3 ] modified F1 width and position vs. the whole of the reply,
4 ] modified XPDR reply frequency.
◆ F1 ⇒ F2
radar " A " is not very sensitive to out-of-norm spacing; radar " B " well, the probability of
detection drops significantly. Inversely, radar A is more sensitive than radar B to the width of pulses F1 &
F2, and, like the Orly radar, more by lower than by higher deviation, dropping to zero for more than 150 ns
from ICAO limits.
◆ C1
same conclusions for pulse width. Both radars decrease in probability of detection, with further
consequence on its Mode C validation in the case of radar B.
◆ Frequency test
Both radar's accept deviations of 9 MHz from nominal. Radar A starts reducing
detection at 13 MHz, radar B at 14 MHz only ! With such a frequency band path, pulses coming from other
systems, like the DME, may interfere and create additional garbling.
⇒
The influence of out-of-norm parameters on the radar data quality is heavily dependant on the radar
receiver and extractor settings.
Some of the out-of-norm values result in a drastic decrease of the radar performance.
The radar accepting wide frequency deviations to cope with such corrupted XPDRs are subject to
increased garbling. What is gained on one side is lost on the other one.
See the complete report in ANNEX 6.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 12
1.2.4
March 1995 : DFS at GöTZENHAIN
The modified EEC transponder has been installed in the surroundings of the ICPMEs ( Calibration
Performance Monitor), and connected to the antenna of the ICPME n°1 , the ICPME n°2 working normally
as a reference.
This building is located near to the New Monopulse Radar, that is just now available before its operational
start up.
The Log Σ video out of the receiver is visualised on LeCroy digital oscilloscope and recorded on a printer.
Plots and probability of detection are recorded at the output of the Reply Processor and Correlator.
Range, azimuth, A & C codes and antenna turn number are printed for each test.
Fewer different tests are done than in the other campaigns.
◆ F1 ⇒ F2
Only a ∆ of 20.2 µs has been tested. Probability of detection remains at 100 %,
even when F1 is 100 ns smaller than nominal.
◆ C1 & F1 - F2
2 out of 3 parameters modified:
1 ] F1 ⇒ F2 20.2 µs,
C1 width 350 ns,
2 ] F1 ⇒ F2 nominal,
C1
"
250 ns
3 ] F1 ⇒ F2 nominal,
C1
"
550 ns only , or with
◆ Frequency test
position : nominal - 100 ns : Pd
and / or
100 %
"
- 200 ns : Pd 90 to 93.3 %
"
+100 ns : Pd
96.7 %
the radar accepts deviations of 1085 and 1093 MHz without reduction of Pd.
This Pd = 0 only when the frequency is 1080 or 1100 MHz.
⇒
These tests although executed at less extreme values, have shown conclusions similar to the other
trials.
See the complete report in ANNEX 7.
1.2.5
Synthesis of the 4 trials
The ANNEX 8 combines in 4 tables the results of the previous tests campaigns.
1.2.5.1 The figures obtained e.g. when two parameters are ONE JUST AT THE LIMIT, ONE 100 ns OUTSIDE, are
dramatic : it means THE REPLIES WILL NOT BE ACCEPTED as belonging to that aircraft !
Logically, if the settings of the (monopulse) radar were based on the strict respect of the ICAO norms, the
extractor should reject ALL replies just exceeding the tolerance window.
It is not the present situation; but in MONOPULSE RADAR THAT ARE NOW INSTALLED, by various
manufacturers, with
- various settings for the extraction criteria
- various capacities of the algorithms to recover from unsatisfactory data,
the corruption of some transponder's parameters or parameter combinations show an influence that is
1 ] sometimes important when 1 parameter is out-of-norm,
2 ] nearly always important when 2 parameters are at the limits or more,
3 ] not predictable from the transponder's end.
It concerns the replies and, although in a lesser extend, the plots.
1.2.5.2 The extraction criteria will be different in the future radar's, all monopulse; certainly they will reduce the
windows inside which parameter are accepted (windows in excess of ICAO limits of coarse); a behaviour
already observed in monopulse radar currently being installed, because of the more sophisticated hence
more outstanding degarbling algorithms.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 13
⇒
To summarise, one can say that :
" In a certain amount of radar stations, out-of norm transponders generate a reduction of the
probability of detection, of correct code extraction and a degradation of the resulting tracks.
This reduction will be increased in all the future radars ".
1.2.6
Other out-of-norm influences
1.2.6.1 Another characteristic that is important for the extractor is the Variation of the frequency inside each pulse
or between the various pulses of a reply.
The decode process is highly dependant on the good shape of the first pulse (F1), through the sensitivity of
the filters; any variation of the frequency is indirectly modifying the pulse rising and trailing edge, hence, the
basis of the other pulses sampling and decoding process.
1.2.6.2 Similar influence is coming from the Amplitude variation, inside each pulse or between the various pulses of
a reply.
1 .3
Tr a ns ponde r popula tion
An inquiry has been addressed in August 1994 to the ECAC countries, concerning proportion of transponders of the
various technologies.
These equipment could be classed into 3 groups, at least that was the only way the data could be collected on a
wide base :
Mode A•C or Mode A
XPDRs with cavity generated radio frequency modulation
{ 91.5 %
Mode A•C
XPDRs with solid state devices only,
{ 42%
Mode S
XPDRs of present generation,
{ 4.3 %
See the table in ANNEX 9 for more complete data.
The variation between the various countries is not too significant, it depends on the relative proportion of commercial
aircraft vs. general aviation; e.g. all aircraft flying to the USA must already carry Mode S XPDRs.
But,
⇒
⇒
the Mode S equipped aircraft are flying the most, being mainly airliners;
the situation is the present one, end 1994, and does not preclude the evolution for the next 5 years.
Indeed a recommendation ICAO / region EUR is issued for equipping all IFR flying aircraft in 1999 with Mode S
XPDRS, but is not yet written into national documents.
At this stage of the inquiry, we do not know when and how the various countries separate or will separate the
IFR/ VFR flights as far as transponder requirement is concerned ( we mean, the aircraft which never fly into spaces
where IFR capability is mandatory, some of them having NO transponder at all); the question arises for the present
situation as well as for after the years 1998 / 1999, where another recommendation concern the VFR aircraft; see
later ( § 2.2 ).
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 14
2
EVOL UT ION OF T HE PROBL EM S
2 .1
Shor t te r m
2.1.1
As already mentioned, the "old" ground stations (extractors) have been adapted to the then existing
situation concerning XPDRs : the " windows" for pulses and replies were wide enough to cope with (mainly
analogue ) XPDR replies that did deviate from the nominal values beyond the ICAO tolerance limits;
indeed, it was considered better to catch the replies, accepting possible reduction of the SSR extraction
quality, than to lose these replies, with the consequences on the aircraft plot and track.
The remaining 3 % (in 1993) of out-of-norm XPDRs produced only a few problems, but e.g. recently an
important one was reported: one radar completely lost the replies of an aircraft in the French control area;
hopefully, other radars did record the replies of this aircraft.
Since a few years, all new stations being installed are monopulse and they are conceived to work with
Mode S XPDRs. So, as stated in the preamble,
⇒
in order to be operated with the best return and to maintain the a high safety level, the present and
the new radars require more accurate transponder replies.
2.1.2
TCAS equipped aircraft also need correct replies from the other aircraft's transponder, in order to issue a
climb or descent recommendation that is coherent with the real situation of the 2 ( or more ) aircraft.
The project of reducing aircraft separation criteria is another element that has to be taken into account. The
increase of traffic in the European skies pass through the reduction of longitudinal as well as lateral
separations; in order to accept this requirement without reducing the safety net, a certainty in the aircraft's
position is essential. This means again no loss of data and accurate XPDR replies, and includes
surveillance of the altimeter function and the conversion of its data to Mode C.
⇒
In the near future, TCAS and separation criteria will also require more accurate transponder replies.
2 .2
C oe x is te nc e of v a r ious ge ne r a tions of tr a ns ponde r s
2.2.1
The transponders of the present generation of Mode S units have a longer MTBF (see § 2.1), but as long
as a batch of old transponders are airborne - and this period of time could be long if no replacement is
mandatory applied - , the loss of replies at the radar input, due to a
XPDR
either completely shut down or
having characteristics seriously out-of-norm, could NOW lead to dangerous situations, not numerous but
dramatic in their consequences.
2.2.2
The ICAO / region EUROPE has issued a recommendation for equipping all IFR aircraft with Mode SLEVEL 3 transponders, for 1998 ( see ref Radar Surveillance Standards). Each individual State should
transcribe it in its national operating rules; up to now, only one has done it.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 15
2.2.3
EUROCONTROL has also issued a proposition for VFR aircraft in Europe: they should be equipped with
Mode S - LEVEL 2 transponders for 1999; this proposition was accepted recently as a recommendation;
but when will this become a national obligation is not yet known.
So, it is evident that in 1999, NOT ALL aircraft, and in particular general aviation, will be equipped with
modern units. We can expect without too much error a percentage of 50 % of Mode S vs. Mode A•C.
Hence, the expected improvement of the situation in respect to general quality of transponders may be
delayed seriously;
⇒
vanishing not so rapidly as desired, the problem of old transponders will have to be treated as a
middle term objective and temporary solution has to be put into force.
2 .3
Futur e s itua tion
Be that as it may, within a certain number of years ( in 2005 ? ), all XPDRs will be Mode S type.
They can be divided into
the present and near future installed units, mostly LEVEL 2
the next generation, mostly level 2 (for general aviation) or LEVEL 5 (for commercial aircraft)
In the first group, some BITE possibilities are present, essentially devoted to technical a-posteriori
maintenance aspects; they are not usable for on-line alert and ATC purpose, being neither oriented
towards surveillance of the XPDR characteristics, neither imposed by operational requirements nor built
around common definitions.
The next generation BITE shall allow such monitoring of characteristics that a part of it could be used for
verification of the good behaviour of the
XPDR ,
that is, it could verify the minimum acceptable set of
characteristics that are needed for ATC surveillance, in other words used for our purpose here.
The aircraft operators trying to reduce their operating costs are very interested in the extensive use of the
BITE possibilities; ATC requests are in this case in full accordance with this objective.
⇒
In order to be effective, decisions should be taken before long, to develop norms concerning both the
functions and elements to monitor and the way these data are transmitted to the ATC.
The BITE " product " will be developed further in chapter 6.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 16
3
POSSIBL E APPROACHES F OR
T RANSPONDER VERIF ICAT ION
3 .1
Pr e r e quis ite s
Aboard aircraft flying IFR (and VFR when equipped with XPDRs),
✍
1
all the transponders must respect the ICAO norm (Annex-10 regulations).
It is probably not economically possible to check permanently all XPDRS, but
✍
2
one should adopt a solution such that at least the largest part is verified regularly through
Appropriate Maintenance as much as necessary for the present and future radar environment;
for the rest, both the exceptions as the sudden failing units being covered with
✍
3
an On-line Alert device, alerting the ATC and the pilot.
One must deal principally (but not exclusively) and rapidly with the large population of old Mode A•C transponders
during the next years. Therefore, one must
✍
4
set up the “solution” within a very short time, covering first the Mode A•C function that is
essential to the safety. Extension towards Mode S functions may be planned in a second step.
The importance of the XPDR in the ATC environment being largely increased, following all what is developed in the
above paragraphs, it seems that
✍
5
the question arises to increase the category of the XPDR, maybe through a new category of
importance. The same is true for other equipment like GPS,...on which ATC and / or navigation is
based.
3 .2
C ons e que nc e s
In other words, the global solution for insuring the transponder completely fulfil its ATC role, is based on the three
aspects
☞
1 an improved
☞
2 a new
☞
3 a
maintenance,
on-line alert device,
rapid implementation
Action 1 should increase the transponder's average quality as well as decrease the number of failures and
unscheduled removals,
Action 2 should detect the suddenly failing units (in reduced number after action 1 is effective) as well as those
coming from countries where ECAC recommendations are not necessarily fulfilled.
Aspect 3 is necessary to give effective results and increase the safety the next years during the coexistence of old
and present generations of transponders and future units using extensively the BITE .
Modifications can be proposed afterwards both to enlarge the solution up to ICAO level and also to cope with the
extension towards Mode S functions.
The way the transponder can officially be raised to an adequate level of importance is
☞
4 an official request initiated at ICAO and JAA level by the EATCHIP Surveillance board, but this
operation is administratively long.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 17
3 .3
Ve r ific a tion pos s ibilitie s
They are various ways of verifying the good behaviour of the transponders:
•
To control all the XPDRs in operation, at some landings or takeoffs ( see § 3.4.1);
•
To control all the XPDRs in operation, at all landings or all takeoffs ( see § 3.4.3);
•
To verify all the available XPDRs of each operator, at the companies premises, through a mobile test
equipment (see § 3.4.2);
•
To verify the XPDRs during scheduled maintenance, through either RAMP or BENCH TESTING;
•
To examine the XPDRs on the ground, after the occurrence of a fault report issued by e.g. the
controller;
•
To examine the XPDRs on the ground, after automatic fault detection by the radar system;
•
To use the BITE function(s) installed in (some generations of) transponders.
The list is not exhaustive; two or more solutions could be combined.
3 .4
Me thods N OT r e ta ine d by the Gr oup
3.4.1
The EXTENDED use of a DATAS - LIKE equipment
This solution would be to develop and to extend the measurement campaigns that EUROCONTROL made
with the MTPA and the DATAS equipment.
This has been abandoned as a permanent solution; indeed
•
the
AMOUNT OF EFFORT, IN TERMS OF PERSONNEL AND COST; various “ copies “ of the
DATAS should be built, personnel should be trained;
•
the
INCREASING DIFFICULTY TO INSTALL this mobile equipment on airports; it was already the
case during the last measurement campaigns; difficulties appear in both technical, administrative and
safety domains;
•
most MODE A-C TRANSPONDERS DO NOT REPLY ANYMORE when the aircraft is on the ground;
•
the
LIMITED AMOUNT OF AIRCRAFT THAT CAN BE MEASURED, leaving huge quantities of
unverified aircraft, especially those who fly seldom in the year and who do not use the main airports;
and these are the ones that carry the oldest and most faulty transponders.
3.4.2
A DATAS - LIKE vehicle at Companies Premises
A variant to the previous concept consists of using such an equipment at the company’s premises. A
vehicle equipped with a modernised version of the DATAS would turn around the hangars of all the
companies and execute ramp tests on all available aircraft.
The vehicle would be built in a few examples and owned by some of the national administrations.
The equipment could be developed by industry and based on existing designs, both DATAS and present
bench equipment.
This approach has not been examined by the Group. Yes, it avoids the administrative and technical
drawbacks described in the previous paragraph, but it still needs efforts in personnel. It is in fact a heavy
bench test set, certainly capable of lots of measurements but unsuitable for measuring and testing ALL
aircraft all the time, and consequently a costly solution.
But the idea can be reused for a Mode S certification tool.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 18
3.4.3
The GTVS
This idea was submitted by some national administrations as an attempt to overcome the problems of the
DATAS idea developed here above.
The GTVS ( Ground Transponder Verification System) would consist of one or a few sensors installed
aside the landing runways, automatically measuring characteristics of the transponders aboard the aircraft
during the last phase of the approach; the sensors would be connected to a central processing unit
(preferably installed in the control tower building) with a connection to the airport control.
Tests consist of both passive measurements of the replies, and active interrogations whose parameters
vary around the nominal ICAO values; the amount of different tests are twice the DATAS possibilities.
For each aircraft showing test results outside the defined tolerances, an alert would be sent to the
controller, for immediate action when the aircraft is "available" on the tarmac.
Two studies have been launched, showing that the concept is feasible. But they are too many limitations :
•
the necessity to
I NS TA L L O NE S Y S TE M O N E A CH MA I N A I RP O RT, in order to cover
most of the aircraft population;
•
there will remain AI RCRA FT S E L DO M O R NE V E R P A S S I NG in front of these installations;
these are principally the small companies and the general aviation using either regional or general
aviation airfields; and this population is the one that shows the largest proportion of out of norm
transponders;
•
the system is
NO T A DA P TE D TO MO DE S E X TE NS I O N : the test time available during
this landing phase ( at a reasonable range) is too short to allow testing of e.g. the protocols, software
packages and datalink capabilities in the Mo d e S transponders; beside, the exchange of some test
messages may lead to misinterpretation by the other onboard equipment linked to this type of
transponders ( ADLP, displays,...) or, worse, in the TCAS co-ordination;
•
the problem of
I DE NTI FI CA TI O N O F NO N- MO DE S TRA NS P O NDE RS equipped aircraft
is still not solved (with the DATAS, this identification was visual, immediate);
•
the deployment of such installation over all Europe seems
TO O E X P E NS I V E A ND WO UL D L A S T TO O L O NG .
•
the difficulty of
IMP O S I NG A N I MME DI A TE A CTI O N
( e.g. replacement ) to the aircraft
operator, when a transponder has been observed, automatically, as probably out-of-norm.
Therefore, the GTVS solution is not proposed.
But a subset of GTVS feasibility studies in the form of a Mini-GTVS could be envisaged, and this point is
examined in chapter 5.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 19
3 .5
Se pa r a tion be twe e n the v a r ious ty pe s of X P DR s
A logical conclusion from various above paragraphs is that one cannot treat all XPDRs in the same way, because
- old XPDRs and modern units ( Mode A•C or Mode S ) do not present the same occurrence of fault:
this is essentially linked to the technology relying on either analogue or digital circuitry;
- unnecessary XPDR lay-downs are not economical and avoided as much as possible by all aircraft
operators;
- present Moder S XPDRs differ from the Mode A•C units by their software contents, that can generate
other types of problems
- future Mode S XPDRs problems could be partially ( and hopefully later, totally) covered by the BITE.
The problems would then be tackled like this :
IMPROVED MAINTENANCE [electrical ]
and, especially
ALERT
Old Mode A*C
XPDRs
Present Mode A•C
XPDRs
Present Mode S
XPDRs
Future Mode S
XPDRs
BITE
&
unscheduled
maintenance
MAINTENANCE [software]
In other words, preventive maintenance rules would be improved for all Mode A•C XPDRs, insisting in particular on
the old units; for the present Mode S XPDRs this concerns their Mode A•C functionality and other electrical
characteristics (see end of § 1.1 in this respect ).
Maintenance aspects of the next generation of Mode S XPDRs would be treated by a BITE solution, based on
effective extended BITE capabilities, but in a form that has still to be studied.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 20
4
ACT ION ON T HE M AINT ENANCE
4 .1
R e gula r m a inte na nc e
Regular or scheduled maintenance is not an aim in itself, it is the way to guarantee, as far as possible, that
THE EQUIPMENT WILL RUN CORRECTLY, within the requested tolerance limits, up to the next test passage:
⇒
T O GUARANTEE : this implies the responsibility of the testing body; technicians and workshops are
approved, but are they well enough controlled ?
⇒
AS FAR AS POSSIBLE : any equipment may fail suddenly during operation, whatever the quality of the
maintenance; this is why an alert system should be joined to the maintenance procedure.
⇒
CORRECTLY : the equipment for testing the transponder must have enough possibilities, both in the
variety of parameters it can check and in the accuracy of the measurements.
⇒
WITHIN THE TOLERANCE LIMITS : the ICAO limits, revised a few years ago as far as Mode A•C is
concerned to be in accordance with the new Mode S equipment, are defined as a function of the
interrogators needs: but in fact, some real characteristics of the transponders could be slightly out-of-norm
without any harm, whereas other ones should be contained within more tighten limits, for a better output of
the SSR monopulse stations.
⇒
UP TO THE NEXT PASSAGE: the periodicity of the maintenance operations should be such that the drift of
some characteristics does not overpass the above limits before the end of the period; there is a main
difference between "old" mostly analogue XPDRs, carrying cavity frequency source, and the more recent
types with digital technology ( including the Mode S units).
4 .2
Ma inte na nc e r e quir e m e nts a nd ha r m onis a tion
4.2.1
The characteristics of national maintenance requirements for transponders have been obtained through the
same inquiry as mentioned in § 1.3 . It is presented in ANNEX 10.
These results show :
⇒
That the authorised verification operator is generally an approved avionics workshop, including both
independent labs as well as the technical services of the large companies; s o m e t i m e s
representatives of the transponder manufacturer.
⇒
A consensus around the FAR 43 regulations, explicitly written or implicitly reproduced.
⇒
The FAR 43 regulations define a minimum list of tests, that is considered by some countries as not
sufficient, so they add a few more.
⇒
A periodicity of 2 years is already adopted by the large majority, for RAMP TESTING.
⇒
RAMP TEST equipment should be improved, but taking into account the large number of units in use,
and the absence of economical pressure to change that situation, it seems that an adaptation of (the
large batch of ) IFR ATC601 units, if technically and financially possible, could be a good solution.
⇒
RAMP AND / OR BENCH : some administrations impose both tests alternatively, some ask for a
ramp only, some for bench only.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 21
4.2.2
To cover the problems of XPDRs passing through the net of the RAMP TESTS, for any reason, (e.g. the
test set is not accurate enough or not capable of measuring some characteristics), it seems necessary to
require BENCH TESTS on a periodical base too; the fact that a few countries request the BENCH TESTS
reflects the early discussion between the original FAA request in favour of using the bench in lieu of the
ramp, for more accurate results, and the users who were reluctant to increased maintenance costs; but at
the time the FAR 43 was introduced, the situation described in the above chapters was not yet present.
On the other hand, BENCH TEST alone is not sufficient; failures at connectors, cables and antennas can
only be detected through external RAMP TEST.
4 .3
O N C O NDI TI O N pr oc e dur e s
4.3.1
Many commercial aircraft operators prefer to follow the so-called ON CONDITION procedures, instead of
the above mentioned general maintenance rules.
A maintenance policy is contractually adopted after agreement between the transponder manufacturer, the
aircraft assembler and the administration; based on the safety level, the MTBF of the unit, the existence of
stand-by units and real tests executed to confirm the theoretical estimations, including drift possibilities, a
scheduled maintenance is fixed, that includes periodicity of the verification, the list of tests and the test sets
to be used; this last can be ramp or bench, it varies.
In the case of XPDRs, the contract generally incorporates the FAR 43 technical aspects as a minimum.
Reasons to adopt this procedure are mainly economical, because in theory the maintenance is exactly
adapted to the type of equipment, so no untimely removal of XPDR should be done, reducing the cost to
the minimum.
4.3.2
The ON CONDITION procedure was too difficult to include in the comparison between maintenance
requirements described above because it varies from one type of transponder to another, from one country
to another.
4 .4
Pr e s e ntly us e d r a m p te s t e quipm e nt
4.4.1
If the maintenance rules have to be adapted or modified, the present population of test sets used in XPDR
maintenance is an essential element to take into consideration, for various reasons including cost.
The inquiry about Maintenance Requirements did contain a list of test sets used in each country.
See the table in ANNEX 10 .
The most often mentioned equipment are the: IFR ATC600 or 600A for Mode A•C Ramp tests , IFR
ATC601 when Mode S extension is used, and IFR ATC1200, -1400, -1403 for Bench tests.
4.4.2
The capability of this equipment to measure each parameter is presented in the tables of ANNEX 11 ;
one column presents the iMPORTANCE OF MEASURING the parameter taking into account
•
the occurrence of faults in the different campaigns ( as listed in ANNEX 2),
•
the records of XPDRs returned to maintenance
•
the theoretical consequences, as they have been developed in the GTVS feasibility studies.
( also in ANNEX 2 ),
Next column gives what is therefore considered as suitable for an Improved Ramp Test set; it combines
both the present test set possibilities and the most important characteristics.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 22
• IFR ATC 600, 600A
It is not capable of measuring
the XPDR interrogation frequency acceptance;
the SLS vs. P1 ⇒ P2 spacing or vs. P1 & P2 duration;
the pulse width;
the position of each pulse inside the reply; this means an oscilloscope is to be used in parallel.
the reply rate should be measured also at a higher PRF, e.g. 500 /s
In general, the accuracy of the IFR 600 ( 600A) is not very good, there it uses an analogue
vu- meter (e.g. for measuring P1 ⇒ P3 or F1 ⇒ F2 spacing).
Its low price makes it a commonly used equipment for Mode A•C.
• IFR ATC 601
A more recent development, it includes :
most of the other RAMP TESTS that are necessary for old Mode A•C XPDRs
but not the position nor the width of ALL pulses, only of F1 & F2
basic Mode S functions
Automated sequencing of measurements is possible in the form of a go-no-go test.
Its relatively high price generally limits its use to workshops or operators who have to test Mode
S Units.
• Other Ramp test sets
have not been examined. Not made available to the Group.
But in principle, they execute the same service.
The last column of the table presents the list of tests suitable for BENCH TEST, established by taking
into account the IMPORTANCE to MEASURE listed before.
4 .5
Te s t Equipm e nt A utom a tion
4.5.1
With the end of DATAS project at the EEC and following the demand for a Mode S protocol test bench, the
Agency decided to evaluate existing test sets. The need to certify the experimental Mode S chain in aircraft
came along with the first conclusions of the STFTV Group : they prompted the EEC to make various
evaluations using an IFR test set. The choice of this equipment follows collected information regarding the
transponder maintenance over all ECAC countries; indeed, it is by far the most used equipment for
transponder testing.
The test was made with an IFR ATC 1400A coupled with the ATC 1403C.
Other tests are being prepared with the RAMP TEST SET ATC 601.
4.5.2
Three approaches were chosen :
• 1 The first concerned only Mode A•C tests on ATC1400A. The aim was to develop software tools to
automate a maximum of complete tests.
• 2 The second dealt with the use of ATC1400A & 1403C, for Mode S procedures. The aim was the
same as for Mode A•C but it adds an automatic test for various Mode S protocols.
• 3 The third approach will be similar to the first two, but deals with the ATC 601 unit.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 23
We have now results for the first approach and, partially, for the second one.
The task was executed in the EEC B2/2 workshop.
The details are presented in ANNEX 12.
4.5.3
To summarise, one can say that
the automation of the existing BENCH TEST SET is feasible, for mode a•c and mode s functions; in the
absence of newly bought test sets, it could both save money, by shortening the time passed on each
equipment and using less skilled technicians, and harmonise the tests executed by all workshops.
Concerning the RAMP TEST SETS, the automation can be done on ATC 601 units only, not with the
most used ATC 600 or 600A ; the possibilities are still being studied, and the ratio added part ( portable
PC, modification investments) to existing part ( ATC 601) may be less interesting for the operator. But it
seems also feasible and the harmonisation would also be an advantage in increasing the level of the
maintenance of the community of ECAC countries.
The following figure shows what the development of such an idea could be:
Mode A•C : more tests
Mode S : hardware
+ a few UFxx / DFxx
Mode A•C :
some tests
Mode A•C : all tests
Mode S : hardware
+ protocol + datalink
Mode A•C Ramp tester
e.g. IFR 600A
Mode A•C•S Ramp tester
e.g. IFR 601
Research on the automation
of the IFR 1400/1403
(PC control & ...)
PC controlled " IFR601type "
capable of outputting all curves
of the Mode A*C*S characteristics
and protocol & datalink tests.
SIMPLIFIED VERSION
COMPLETE VERSION
PC / µP controlled ramp tester
used in GO-NO-GO
capable of outputting on printer
the curves of the bad characteristics
PC controlled bench tester
capable of outputting
on PC display all curves
and sequences of test and
on-line desirable changes
But it is linked to the willingness of the relevant company or any other doing such equipment, and this is not yet
obtained.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 24
In fact,
Operators ( in their workshops) need
a RAMP TEST SET faster, mode s capable, protocol capable, run by a PC or µP,
a BENCH TEST SET also automated, with more outputs (printer, PC displaying curves, access to
maintenance documentation and record).
Administrations and transponder manufacturers need
a BENCH TEST SET with the same capacities as above plus an increased choice of tests, of Mode S
sequences ( including protocol exchanges) and with higher accuracy .
4 .6
Pos s ible r e s tr a ints
4.6.1
The way the XPDRs are maintained or repaired is varying from one country to another and between the
various workshops inside each country, because of
4.6.2
•
different regulations
•
workshop load
•
operators financial situation, size of the company
•
different technician's habits ( use of oscilloscopes, ..)
Generally, the XPDR returned to maintenance workshop is checked whether it respects the tolerances
indicated in ICAO-Annex-10 or not, in other words if a characteristic lays somewhere inside these limits
e.g. a reply pulse appearing 95 ns later than the nominal position, 100 being the limit), the setting is NOT
modified. As a consequence, a later drift of any component will possibly bring this characteristic out of
norm in a near future, that is to say before the next passage in maintenance.
4.6.3
The existence of old XPDRs (with their old maintenance manual ), that are no longer in production,
prevents any retroactive influence on their maintenance procedures. Sometimes, the manufacturer does
not exist anymore!
4.6.4
With the large population of test sets installed, any technical improvement in the testing area is dependant
on the willingness and financial situation of
4 .7
•
test sets manufacturers
•
operators
•
workshops ( whether owned by the operator or independent).
Lis t of pos s ible im pr ov e m e nts
Maintenance of Mode A•C and present Mode S XPDRs could be improved by adopting one or more of the following
propositions:
1
Geographical extension : the " best " rules ( e.g. to apply the 2 years periodicity) would be adopted
in common by all countries, that is, an harmonised requirement applicable to all ECAC states.
2
Reduction to a 1 year periodicity (for all / for some types of XPDRs).
3
Specific requirement for old XPDRs , that is when aged more than 12 years, because this
duration has been observed in the last measurement campaigns as representative of age-related
failure increase; this is shown in § A2.7 of ANNEX 2 .
4
• STFTV •
Adoption of harmonised BENCH TEST REQUIREMENTS.
[
Final Report to SURT ][ May 1995 ]
page 25
5
Re-setting to the nominal value the characteristics of any XPDR returned to workshop,
WHATEVER the reason, in lieu of just verifying if it lies within the tolerance limits.
6
Automation of the test equipment’s in view of easing and shortening the test procedure.
7
Acquisition of new BENCH & RAMP TEST SETS.
8
Maintenance workshops inspected more often (like in some country, where they are inspected
twice a year), both in terms of test equipment and the way the technicians do use them.
In fact, this procedure is linked to the present status and future developments of the JAA's
JAR145 " Approved Maintenance Organisations" document.
It is not possible to wait for the natural replacement of the test sets, it would last too long; besides, if the
obligation to carry Mode S XPDRs in IFR aircraft and, even more important, in VFR aircraft, was made
effective in ALL ECAC countries in the shortest possible time, it would ease but not eliminate the problem;
indeed, as mentioned before, the new Mode S units are also subject to electrical and software problems.
4 .8
Pr opos itions
4.8.1
As a consequence of what is written before, in particular of
what is done ( in one or more countries),
what can be done with the existing test sets,
the existence of old transponders,
the necessity to avoid unjustified maintenance cost increase,
the increase in replies accuracy required by monopulse, TCAS and separation criteria,
the obligation we have to insure the safety of ATC concerning XPDRs,
the Group proposes the following, for the next years of coexistence of Mode A•C, Mode S and Future
Mode S transponders:
A • Regulations for all aircraft
Maintenance regulations for transponders that are to be reproduced identically in all mandatory national
texts (including the On Condition contractual rules) :
✍
1
To use the existing FAR43 measurements complemented by
the F1 ⇒ F2 spacing measurement and
the Mode A•C acceptance vs. P1 ⇒ P3 spacing verification,
for RAMP TESTING ( it is yet possible with the now available ramp test sets).
✍
2
To set up a periodicity of 1 year for Ramp Test,
2 years for Bench Test.
✍
3
To request a yearly Bench Test for all aircraft and transponders older than 12 years (or when
the age of the transponder is unknown). During this operation, more characteristics should be
controlled, as
SLS vs. P1 ⇒ P2 spacing,
delay time,
reply % at a PRF 500,
Mode A•C acceptance vs. P1 & P3 width, and width of all pulses.
✍
4
By each passage on the bench, whatever the reason and the periodicity, the characteristics
would be restored to the nominal values.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 26
B • Other Requests
✍
5
To establish national procedures that allows EUROCONTROL to get access to measurement
records of the transponders brought to workshop ( status before repair or adjustment).
✍
6
To insure that workshops are inspected on a sufficiently frequent basis.
✍
7
To encourage the European transponder manufacturers to produce low cost Mode S LEVEL 2
transponders, replacing the existing population of Mode A•C units for the bulk of General
Aviation.
They should be in the same range of products and should have the same size for allowing
direct replacement at the minimum installation cost.
( U.S. manufacturers already prepare these units, aiming at a price only twice that of similar
Mode A•C units; European manufacturers also have units).
4.8.2
The propositions nº 2 & 3 will probably have an effect on the aircraft operators in general; higher cost of old
transponder maintenance will be an incentive to earlier replacement by Mode S units ( see proposition 7).
If this replacement is really and seriously accelerated because of the present propositions ( when adopted),
the benefit will be for all the ATC environment !
The 2 years periodicity for Bench tests is estimated necessary to reduce the proportion of old transponders
failures and their failure rate.
It is necessary to get much more data on the particular Mode S functions ( and failures) and the request
n°5 is a way to achieve this goal.
It would permit to conclude on what parameters should be tested definitively and with what periodicity,
allowing
⇒
⇒
4 .9
to adapt that periodicity, if necessary;
to define the minimum characteristics of new RAMP TEST SETS.
J us tific a tions
The following questions might be raised by aircraft operators and maintenance representatives; see here the
answers that would be given :
???
: If the characteristics as measured by ramp test sets lie inside the ICAO limits, why do more ? There is
no mandatory request for more accuracy .
REPLY :
It would be true but nothing is perfect, neither the XPDR, nor the radar; in addition,
1 ] garbling reduces the radar extraction possibilities, and elaborated algorithms do perform less when
replies are not nominal; see also § 1.2, when 2 characteristics are near the limits;
2 ] monopulse radar need higher accuracy (see the introduction), and when they will be strictly
adjusted, ANY small deviation, now covered by the relatively wide tolerances, will be rejected;
3 ] test set measurements are not perfect;
4 ] drift ... ( see § 4.8, proposition 8).
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 27
???
: Ramp test every 2 years is enough .
REPLY :
the observed remaining 3 % of out-of-norm XPDRs contradicts that argument, e.g. in the countries
where the 2 years periodicity applies; the shorter this periodicity, the lower the risk of characteristic
drifting out of norm.
???
: Bench tests are not necessary, as all the test are executed by ramp and, besides, the FAA does not
request it .
REPLY :
the accuracy of a vu-meter is not very high, and makes it difficult to set back to nominal values; the
Ramp test set does not measure all tests that are deemed necessary now, and other ones that we
believe suitable as explained in § 4.4 and in Annex 11 (SLS, delay time, frequency acceptance, accurate
Mode acceptance).
???
: Further, when the FAR 43 was issued, the consensus came for ramp test only, not for bench test .
REPLY :
1 ] this was done under pressure of the operators, we believe, because of cost;
2 ] no long statistical experience did exist, concerning out of norm characteristics;
3 ] more accuracy is now needed because of monopulse processing techniques.
???
: Request for older than 12 years XPDRs will be outdated when Mode S XPDRs replace them.
REPLY :
If at that moment, all " old XPDRs " will have beenreplaced, it is OK, the request will be without effect;
but also without any harm!; and if, as we foresee, there still exist s a certain number of these old units,
they will be even more concerned, compared to the " modern " XPDRs, in the monopulse environment.
???
: Aircraft operating ON CONDITION XPDRs should be kept out of these requests .
REPLY :
If these conditions satisfy at least with the proposed maintenance regulations, no problem should occur.
???
: Bench test is costly, and ramp test every year also; extra cost will be 4 man-hours every 2 years,
at 40 $ per hour, plus extra test set investments .
REPLY :
1 ] It still remains below the normal cost of Mode S XPDRs maintenance costs; even with extra test
sets, for the provision of which we multiply by 2 :
(40 $ x 2 ) x 4 m-h / 2 years / 1800 flight hours / years = 8 cents per flight hour .
( the maintenance cost of a Mode S unit is about 15 cents / flight hour)
2 ] the use of the oscilloscope is often needed ; the proposed automation should ease the work and
reduce the amount of time passed on each unit.
( Even at higher labour cost, say 70 $ / hour, the figures would reach 14 cents / flight hour ).
???
: Some small operators will not be able to buy new ramp test sets for economical reasons.
REPLY :
That's why we propose to reduce the periodicity of ramp tests and make more often bench tests, using
the test sets that exists anyway in normal workshops.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 28
5
5 .1
AL ERT DEVICES
R e a s on
As developed in chapter 3, the existence of transponders that either may suddenly cease to reply and also
because we have no control on what happens outside ECAC countries concerning maintenance,
a safety net must be placed in a certain way to avoid any risk of losing an aircraft
in an SSR only environment.
5 .2
Te c hnique
The persistent loss of data at the controller’s end of the radar chain should generate an alert. The same
could occur when e.g. the altitude or the code is modified suddenly.
This type of alerting does not exist now [ note ] , at least not on a systematic or automatic basis; faults
reports have been issued since many years by controllers, but in a limited set of situations; for this to occur,
either the transponder or the chain transponder-to-antenna has a big problem or the data received have
been corrupted by repeated unexplained data corruption.
Note : In some radar stations, some altitude alert exist already: triggered when the altitude, as received by the plot
extractor, presents an excessive change compared the previous data; the controller is then informed.
Slight deviations of the transponder that provoke temporary corruption are much more frequent and slip
through the net.
The ALERT device must
•
detect the important failures, automatically;
•
not disturb without reason the controller's work;
•
receive an efficient follow-up.
Three approaches are considered :
•
the detection by RDPS
•
the use of RASS-S tool
•
the use of a mini-GTVS.
All are technically housed aside the SSR equipment, needing no external equipment, neither building nor
antennas, removing the main drawbacks of other propositions described in chapter 3.
These solutions are described in the next paragraphs 5.3, 5.4 & 5.5.
5 .3
D e te c tion by R D PS
5.3.1
To detect automatically a defective transponder and to present a flashing alert to the controller when the transponders data is not coherent with its earlier values or, in a multiradar environment, with
those received by other sources - seems an interesting approach.
The idea of using ground infrastructure at centre level was submitted to the Radar Visualisation Service, in
charge of the RDP S ( Radar Data Processing System) in France.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 29
The RDPS has been developed in such a way that the "bad" transponder replies do not reduce their
capacities; in this context it seems incoherent of getting out information concerning bad of missing replies;
many difficulties would appear because of code A ↔ code C correlation, insufficient updating of altitude;
one cannot diagnose a bad replying transponder from local or multiradar anomalies if they concern aircraft
in garbling or fluctuating (e.g. turning ) conditions; the fact that the radar systems are relatively immunised
against corrupted or missing data implicitly plays against the use of these systems for detecting "bad"
transponders.
The first conclusions are not enthusiastic; the chances to validate the concept are estimated around 50 %.
One should have to modify or adapt these systems, to extract the desired data. To develop an analysis of
the replies, an unmodified video signal is necessary.
The proposition is described in ANNEX 13 : Detection of out-of-norm transponders by the SSR
Let us give the principles hereafter.
5.3.2
Basic Idea
5.3.2.1 The idea
would consist of adding in the present interrogators an extra processing chain at the output
of the receiver upper stage, in parallel to the operational chain ( that is generally already duplicated
because of data availability).
This special chain would deliver tracked plots just like the operational chain. These plots would be
extracted through a more " severe" chain, that is, the settings would be strictly adjusted to the ICAO norms.
Plots coming out of this special chain would be compared to those of the normal chain. In case of repeated
losses in the special chain, one would set a " dubious transponder " field in the final plot data at the output
of the radar (ASTERIX format).
5.3.2.2 In monopulse interrogators :
here, the "normal " chain will become more severe, that is, with reduced
reply acceptance windows. The added chain would then become " less severe", all replies, including
those NOT passing through the normal chain or passing but with a bad quality flag, would be accepted
because of both larger " windows" and in depth logic, resulting in the following consequences:
•
The "bad" replies are analysed in details and out comings can be used for both alert and maintenance
purposes, by adequate recordings.
•
Their corrupted data transmitted further down by the ASTERIX format with special flags towards the
controllers displays.
•
All replies passing through this special chain, it realises the SAFETY NET, a role played in the past by
the primary radar.
5.3.2.3 The figure next page
shows how the arrangement of the chains could be, whatever the radar.
The different elements of the special chain are so placed as not to interfere with the presently operational
equipment. The dotted lines shows the various possibilities to interconnect data; the studies should
determine the best ways.
5.3.2.4 Limitations :
The relative simplicity is paid by
•
no diagnostic of the failure;
•
detection works only on Pulse form and positions;
•
it does not work in garbled conditions;
•
the altitude filter in the controller's display must be switched off.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 30
RECEIVER
( x2)
EXTRACTOR
( x2)
SPECIAL EXTRACTOR
- different windows
- different logic
SPECIAL ?
TRACKER
TRACKER
(x2)
COMPARATOR
DISPATCH
ASTERIX formatted PLOTS
5.3.3
Multi-radar extension :
5.3.3.1 The mono-radar information "dubious XPDR" carried by the ASTERIX format is sent in the multi-radar
processing system of the control centre, where it can be correlated with the same data coming from the
other radar. This reinforces the validity of the message displayed to the controller.
The concerned airspace would be those covered by at least 2 SSR radar and would exclude all areas
where the information would not be sure in regard to the radar coverage. Although this exclusion is
seemingly extended in surface, the volume of traffic in the airspace under control plays in favour of this
solution.
The system is based on the splitting of the space in individual volumes in which each coverage is defined.
The XPDR would be detected as faulty if, in absence of garbling,
•
at least one radar does not see the aircraft,
•
this situation persists a certain amount of antenna turns ( number fixed by experience).
5.3.3.2 Limitations :
•
One radar can be for the time being partly failing;
•
The altitude given by the Mode C, must be integrated with care, there it could suppose the presence of
the aircraft in another individual volume than the real one.
Besides, the Mode C data depends on the QNH, while the volume is determined on a pure geographical
altitude.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 31
5 .4
U s e of the R A SS - S tool
5.4.1
The RASS-S
( S for Site ) is a Real Time Monitoring device that, under the master ship of the existing
RASS-C ( C for control Centre ), analyses the performance of all stages of the radar processing, from the
antenna down to the video, in order to control the good behaviour of the radar chain and make the
comparisons / readjustments / repair possible with the shortest delay.
A working paper in ANNEX 14 describes roughly the RASS-S project.
The system is able to both extract and re-inject data in the chain.
The monitoring of the chain radar sensor - ATC control centre needs to send to the RASS-C tool data that
are either " perfect " or real ones: S & D video recorded by the RASS-S are re-injected off-line to test the
good behaviour of the rest of the chain through the RASS-C, under the master ship of this last one.
5.4.2
It was not intended to include the transponder in the monitoring, but some of its parameters may be
apprehended through the analysis of some available characteristics of the replies when they pass through
the above described chain: frequency, frequency deviation, reply power & pulse shape.
5.4.3
The idea of using this tool for XPDR comes not only from the STFTV side, but also from the RASS-S radar
tool management : indeed, if some faults appear on video or plots, the monitoring device must be able to
make the difference, to detect the source, radar or transponder.
5.4.4
Possibilities and limitations :
•
The amount of recording is not unlimited; either all XPDR's possible data are recorded inside time and
geographical limits ( " windows"), or only some characteristics are observed quasi continuously;
•
The system should be related to the flight plan processor, making it possible to affect received data
about "bad" XPDRs to defined aircraft registration;
•
The problems lies partly in how to report a " bad" performance, that is, what algorithm to develop
before giving a flag of " low quality" to the relevant message ( say, in the ASTERIX format);
•
Multiradar coverage can also be used by multi-RASS-S directed to on RASS-C central management.
The difficulties are similar to those described in RDPS multi-radar.
5 .5
U s e of Pa s s iv e GTVS
The third approach is the passive GTVS ( also called mini-GTVS ), proposed in the GTVS feasibility studies, as a
low cost alternative.
5.5.1
The passive GTVS consists of a receiver and processor which is connected to the appropriate outputs of
an (approach) MSSR system. This GTVS system uses the MSSR antenna to capture the XPDR signals.
Two solutions are possible :
•
The passive GTVS has its own receiver and is connected via directional couplers to the test outputs of
the MSSR system, to the MSSR receiver video outputs and to the MSSR extractor outputs,
•
or
The passive GTVS consists only of a signal processor and general purpose computer and uses only
the MSSR receiver video signals to evaluate the XPDR characteristics.
As no special interrogations are produced, only passive testing is possible.
5.5.2
Seemingly, more data can be extracted than through the other RDPS or RASS-S tools:
pulse shape, frequency, power; amplitude deviation, sensitivity; dead time, suppression time;
Mode C validity, P1P2 ratio SLS; delay time; and some Mode S electrical data.
If these data can really be apprehended, it looks interesting. But it depends heavily on the MSSR receiver
capacities.
Still, some limitations of the complete GTVS are conserved, like aircraft identity or ATC controllers
workload.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 32
5 .6
Follow-up
The efficiency of the alert, as far as general safety is concerned, implies that the procedure following the
detection must become automatic and the information be transmitted immediately to the right service. In
other words :
⇒ 1
It must send an alarm to the controller when and only when an important failure of transponder or
transponder reply appears; that is, the XPDR reply failure detection should be limited to the main
parameters, that can have a direct influence on safety.
For the characteristics that are less important (providing they could be measured) for the radar as far as
safety is concerned (those only reducing slightly the quality of the detection and associated algorithms), the
system should have a different follow-up directed towards the transponder maintenance services.
⇒ 2
The pilot should be informed.
⇒ 3
The maintenance service at the next landing should be informed to replace the transponder.
This follow-up is far from being easy to implement, because of many communications, procedures and
persons involved, and because it occurs only from time to time.
Presently, only BITE equipped onboard equipment follow an quasi-automatic way. See chapter 7.
For all the presently used XPDRs, the alert can only be issued by the ground station. An official and
commonly adopted form of transmission that implies the pilot, at least, up to the maintenance service
should be proposed by operational and specialist in the maintenance domain. And this whatever the
importance of the fault detected by the alert system.
5 .7
Pr opos ition
5.7.1
Even if the achievement of the above described systems does not call into question the present monopulse
extractors, their implementation will need a study & development phase, including the new specialised
chains and the relevant algorithms. Next will come a retrofit of the existing installations.
The problem lies in the time scale. To shorten the duration of these studies, the Group proposes to launch
feasibility contracts; to gain the largest benefit, they should be addressed to the manufacturers already
working in these domains (e.g. radar development manufacturers for the RDPS).
5.7.2
The RDPS proposition and the RASS-S tool are in fact not too different, as far as the XPDR verification is
concerned ( one difference : in the RDPS solution, the special chains are particular to each system, only
the procedures would be developed with the same basis and characteristics; in the RASS-S tool, normally,
the monitoring system would be identical for all sensors).
It is not impossible that the final solution could be found by COMBINING ideas out of the three approaches
described above.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 33
6
BIT E POSSIBIL IT IES
6 .1
The B ITE pr opos ition is for the long te r m
6.1.1
The Built-In-Test-Equipment is a sub-element of an equipment that analyses or just collects data (electrical,
software) inside the relevant equipment, in order to inform the "user" of its good or bad behaviour. The user
may be a maintenance system, as seen thereunder, or any other interested system or physical person :
e.g. the maintenance services, the ATC control, the aircraft operator...
The collection of information is generally recorded and transmitted, to the "user" on-line or not, depending
on the urgency of the situation.
6.1.2
Although installed in the first generation of Mode S XPDRs, the resources of the BITE and associated
Central Maintenance System are devoted to rough maintenance problem solving; so it is not usable as the
alert device as we need for ATC.
In the next generation, now engaged, the BITE possibilities are increased to more sub-elements and
functions of the XPDR, including inputs and outputs.
Still, this "product" is presently developed by avionics manufacturer and installers.
6 .2
B a s ic pr inc iple s of C e ntr a l Ma inte na nc e Sy s te m - C MS
A rough description of these principles, valid for all LRU ( Line Replaceable Units) is given in ANNEX 15.
Let us summarise here the elements usable for our XPDR problem :
6.2.1
A central computer-based system ( CMS ) collects data from all possible units (including the XPDR), more
precisely the BITE output of each; e.g. 4 times per second, the status of the unit is analysed and stored in
the CMS memory, normally for off-line examination by maintenance technician: after landing, they control
the contents through a MCDU display and a " tree " approach technique.
By some companies, data concerning a problem "discovered" by the BITE may also be transmitted directly
or indirectly to the ground maintenance.
In parallel to this maintenance line, the software of the operational system may send an alarm to the pilot,
for information or action.
6.2.2
The reason for installing such a tool is cost and simplification: the ratio MTBUR / MTBF, representing the
amount of unscheduled removal, is far too high, that is, too many removals are untimely done, which
signify cost and sometimes aircraft re-routing, because an apparent faulty function was detected, even
without affecting the aircraft's flight safety. This last case, although occurring rarely, is extremely
expensive, costing much more than the price of a new unit!
6.2.3
The present policy is to multiply the amount of parts and subparts controlled by the BITE and also to
multiply the BITE equipped units aboard the aircraft. There is a danger to have too much complexity in this
system that could lead to false alarms induced by the control system itself; therefore, a compromise is to
be obtained.
6.2.4
Each equipment manufacturer has to present a quality analysis of such BITE equipped units in order to be
approved under the so called On Condition procedures.
6.2.5
No official norms exist for the moment that would define the BITE analysed elements, only some
recommendations ( under ARINC 624 ).
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 34
BITE
INPUTS
OUTPUTS
software
modules
RF
hardware
modules
6 .3
CMS
Mode S
to ground
For the pur pos e of A TC s ur v e illa nc e
The need for radar surveillance is slightly different. It is more an ON-LINE MONITORING that is requested,
the BITE being oriented towards verification of characteristics defined by the ICAO Annex-10 regulations,
both software as hardware wise.
A subset of this can be to extract only the parameters that are important for the alert system, in particular
those having an influence on the monopulse radar behaviour.
The information (e.g. a degradation of the XPDR performance ) should be transmitted to
•
the pilot (1)
•
the ground ATC controller (2)
•
possibly any other TCAS operating aircraft in the surroundings (3)
(1) - if immediate independent action is necessary, e.g. switching to the spare XPDR or antenna,
- if the controller has to be informed;
(2) - because the controller must be aware that replies are probably corrupted or missing, with all the
possible consequences on the control procedures;
(3) - because the pilot of any crossing aircraft must be aware of the not reliable data it receives.
6 .4
Tr a ns m is s ion
The data here above can be transmitted to the ground by
•
either a XPDR datalink message (an AICB), if the XPDR is capable to reply albeit in a reduced manner,
or
•
by any other available transmission channel defined in the ATN.
Conversely, an alert having been triggered at the control side, a CommA should be sent to the aircraft; in
case of impossible transmission, then a radio message would be used.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 35
In itself, the BITE is only the origin of the concept, the rest is relevant to the Central Maintenance System;
see the following figure :
Aircraft system
Operational data
Maintenance data
Flight Warning
Computer
EIS indication
or
Local indicaton
Central Maintenance
Computer
MCDU
printer
data
loader
ACARS
pilot information
VHF
Log Book
CMS report
Company ( ground )
LRU fault paper
6 .5
Pr opos ition
The present evolution by aircraft and equipment manufacturers is to reinforce the capability (increase the controlled
functions) and the accessibility of BITE information. The pressure comes from the aircraft manufacturers and,
indirectly, from companies. The evolution of the technology makes this pressure easy to support.
In this view, we have to find different opportunities of using this system in transponder surveillance and verification.
Up to now, little information on how the BITE works is available from the manufacturers, almost certainly for
industrial reasons.
The Group proposes
■
To study the possibility, for new equipment, of using an extended B.I.T.E., measuring those
parameters that are important to the ATC, in particular for the monopulse, in Mode A-C and Mode
S functions.
A contract could probably be placed by a common group of European equipment manufacturers
and aircraft assemblers. They are THE teams handling the BITE elements, knowing their
implications and the companies needs ( e.g. transfer of information to the ground already made by
some operators).
■
To add these B.I.T.E. data to the list of AICB / CommA messages that can be transmitted to the
ground ( when necessary); first through the DATA LINK channel of the Mode S, possibly later
through any other air-ground communication channel.
It is a long term action; through the ARINC - and probably the RTCA and EUROCAE - groups, the ECAC
community should urge the manufacturers to include this extended BITE in their equipment; with the aim of
making it mandatory in the middle term.
It could help a lot by the fact that solving the problem for the largest part of transponders ( within x years,
the Mode S units ); it will drastically reduce the workload of the ground alert system.
Remember, it does not cover the classic transponders, nor the present Mode S units.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 36
7
CONCL USIONS
In conclusion to the report, it is proposed:
1
To adopt the Improved Transponder Maintenance procedure defined in paragraph 4.8
[ § 4.8 propositions 1 to 4 ].
2
To assemble more data concerning transponders tested on the bench, whatever the reason
for removal, including the Mode S faults; the EEC would be the focal point of this collection.
[ § 4.8 proposition 5 ].
3
To introduce discussions at the JAA level, to see how the transponder can be reclassified at the
adequate level. Presently, there are no maintenance regulations installation certificatio only exists.
Discussions should start with the JAA administration to reach a common understanding about
transponders maintenance workshops.
[ § 4.8 proposition 6 ].
A member of the Group should be officially mandated by the SURT to JAA authorities.
The SURT should also find a way to encourage European manufacturers to produce low cost
Mode S level 2 transponders.
[ § 4.8 proposition 7 ].
4
To engage the alert concept developments, through the 3 ways (RDPS, RASS-S &
PASSIVE GTVS ), providing the SURT would approve this. At the end of this study phase,
a choice should be made, possibly mixing the 3 approaches.
[ see chapter 5 ].
5
To collect more information about the B.I.T.E. functions, in present transponders and those in
development.
Having difficulties to receive replies from the manufacturers concerned in the absence of
commercial interest and / or fear of communicating information to competitors , the Group
should be assisted by the SURT in this task.
[ see chapter 6 ].
6
To complete the evaluation of RAMP & BENCH TEST SETS automation and to engage a
BENCH TEST SET policy to assure the fulfilment of procedures defined by the group and
to promote the appropriate tool; this includes the BENCH UNITS needed by the Administrations.
[ see § 4.5 ].
Future tasks include assessing the influence of Mode S electrical faults, their occurrence and their effect on the
TCAS system.
• STFTV •
[
Final Report to SURT ][ May 1995 ]
page 37
--
-- ANNEXES --
ANNEX 1
EUROCONTROL AIC nº 3 ( 20 Aug. 1992 )
ANNEX 2
Occurrence of Out-of-norm Characteristics
ANNEX 3
STNA Records of XPDRS returned to Maintenance
ANNEX 4
STNA Notice to Airlines ( 1993 )
ANNEX 5
Influence of Out-of-norm Characteristics on Radar Data:
--
a] January 1995 : STNA - EEC -THOMSON SDC
ANNEX 6
Influence of Out-of-norm Characteristics on Radar Data:
b] January 1995 : RVA Brussels Airport
ANNEX 7
Influence of Out-of-norm Characteristics on Radar Data:
c] March 1995 : DFS at GöTZENHAIN
ANNEX 8
Influence of Out-of-norm Characteristics on Radar Data: Combined Results
ANNEX 9
Transponder Proportions in the ECAC Countries
ANNEX 10
Maintenance Requirements in Each Country
ANNEX 11
List of Parameters and Test set Possibilities
ANNEX 12
IFR Test set Automation
ANNEX 13
Detection of Out-of-norm transponders by the SSR (incl. Multi - Radar )
ANNEX 14
Working Paper on an Initial RASS RTQMS ( Real Time Quality Monitoring System )
ANNEX 15
Present BITE in Airborne Equipment
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 0
ANNEX
°1
Guidelines for the Monitoring of SSR Transponder Performance
EUROCONTROL AIC nº 3 ( 20 Aug. 1992 )
1. Secondary Surveillance Radar (SSR) is widely
used routinely, as an integral part of the air traffic
system, to obtain real time data on aircraft
(identity, position and altitude). While ground
installations are being constantly improved to
support the highest level of efficiency in the
provision of air traffic services, numerous
deficiencies in the performance of airborne SSR
installations continue to be observed. The faults
can affect the overall SSR system and may lead
to refusal of an air traffic control clearance to enter
airspace where the correct functioning of the
airborne SSR equipment is mandatory, and where
the transponder provides data vital for the flight
safety of aircraft in that airspace.
2. The EUROCONTROL data collection campaigns,
with the Mobile Transponder Performance
Analyser (MTPA) calibrated to conform to ICAO
specifications, have continued. The main
transponder malfunctions detected by the MTPA,
are in pulse width and spacings, signal frequency,
side lobe suppression, receiver sensitivity and
transmitter power. Additional anomalies continue
to be observed by ATC. Incorrect, or degraded,
SSR information significantly reduces the safety of
all the aircraft in the ATC system, and will
increasingly result in economic penalties, to the
operators, when aircraft are refused permission to
proceed. A recent campaign carried out at
Frankfurt Airport has shown that the situation has
not improved. This evaluation was conducted
using the Data Link ad Transponder Analysis
System (DATAS), the successor to the MTPA
equipment.
• STFTV •
[
3. At present, EUROCONTROL is carrying out a
feasibility study into the development of a Ground
based Transponder Verification System (GTVS)
for location at the principal traffic handling airports
of individual States. It is intended that GTVS will
automatically notify the ATS unit issuing
clearances, of aircraft transponder faults that will
significantly affect the flight safety of the individual
aircraft, or degrade the ATC system. Clearances
for such an aircraft may not be given.
4. It remains essential that operators take all
necessary measures to ensure that the technical
performance of transponders strictly adheres to
ICAO specifications Annex 10 Volume 1.
Preventive action should be actively pursued by
the regular monitoring of the performance of the
on-board equipment, comprising transponders,
aerials and cabling. Routine transponder
functional verification to ICAO specifications is
required when aircraft renew their certificates f
Airworthiness.
5. The progressive implementation of monopulse
SSR and the associated ground systems, which
will not tolerate transponder performance even
marginally outside ICAO specification, will
preclude, or significantly delay, the entry of noncomplying aircraft into SSR mandatory airspace.
Final Report to SURT ][ May 1995 ]
page A 1
ANNEX
°2
Occurrence of Transponder's Out - of - norm characteristics
A2.1
Data sources
a - MTPA campaigns results 1984 - 1988.
b - DATAS campaigns results 1991 - 1993
c - STNA audit on the maintenance workshops records in 1994.
d - EUROCAE observations of maintenance workshops.
A2.2
♦
Results
Global figures : 15 % of the aircraft in 1984, decreased to 3 % in 1993, did show one or more characteristics out
of norm.
♦
But in 1993, still 15 % of the OLD aircraft (those carrying OLD transponders) did show faulty characteristics.
A2.3
Types of faults
The column STNA is not comparable to the MTPA and DATAS ones, because the BASE of percentage is completely
different: for the STNA records, it refers to the XPDRs returned to the workshop, for normal, scheduled maintenance
or after a failure has been announced or supposed; for the MTPA and DATAS campaigns, it concerns all the aircraft
landing or taking off during defined periods of measurements.
Type of fault
MTPA 1984-88
DATAS 1991-93
in % of measured aircraft
Frequency ( output XPDR )
Reply percentage
Power
( output XPDR )
Sensitivity ( MTL)
Pulse positions
Pulse width
Delay time ( P3 ⇒ F1 )
Suppression time
SLS vs. P1 / P2 ratio
SLS vs. P1 ⇒ P2 spacing
Mode acceptance vs. P1 ⇒P3 spacing
Mode acceptance vs. P1 & P3 width
Total failure
2.7 *
?
2.0
?
1.9
(4.7)
2.0
0.8
?
?
3.0
0.7
0.8
4.7
≅ 1.0
≅ 0.2
0.7
0.3
?
0.8 ( to > 10 ) *
?
?
2.6
( 20 .4 ) **
STNA records
in % of XPDR s returned
to the workshop
7%
24 %
12 %
3%
27 % ***
3%
7%
?
?
?
[1, 2 ]
[2]
[2]
[1]
[3]
?
?
5%
Notes:
?
not measured or insufficient data
*
general aviation NOT counted ( their value is twice as large )
**
error common to a group of transponders, by construction or workshop habits
***
here, only the F1 ⇒ F2 spacing has been recorded.
[1], [2], [3] : see § 2.4 next page
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A2 - 1
A2.4
Faults origin
(1) Bad settings : - insufficient test equipment ( e.g. too large quantum or inaccurate vu-meter);
- inappropriate personnel action (e.g. the technician does not adjust the parameter when
it lies inside the tolerance limits);
(2) Time degradation of the equipment ( e.g. power section or more rapid drift), even when the manufacturer adopts
acceptance windows that are more tight than in ICAO-Annex -10 .
(3) Partially caused by manufacturing concept bugs.
A2.5
Remarks
♦ In contrary to the theoretical study ( e.g. GTVS Feasibility Study INTERSOFT ), no link seems to exist between
frequency and F1 ⇒ F2 spacing deviations (see source [a] )
♦ the OLD cavity transponders are as faulty as other OLD transponders.
A2.6
Comparison
Although not obtained by the same means, the MTPA, DATAS and STNA results present mostly the same important
faults, at least for the parameters that have been checked : Frequency, reply power, pulse position and delay time
are subject to main problems. STNA did not ask to record the SLS or Mode acceptance possible faults.
A2.7
Special observation : aircraft aged > 12 years
In the last DATAS campaigns, the following faults were observed, as a function of the age of the aircraft ( true faults,
not only near the limits ), which corresponds generally with the age of the transponder or its generation :
Campaign Frankfurt 91 : all faulty aircraft are aged > 12 years except :
a few regional aircraft built in
87 - 91 ( fault : freq., % of reply )
2 same old type
80 - 82
“
“
Tupolev aircraft ( 22 times)
Campaign Orly 93:
all faulty aircraft are aged > 12 years except
one regional company with one type of small aircraft,
one large company with same old version aircraft,
all built in 88 ; the fault : Mode A acceptance. vs. pulse width
Campaign Gatwick 93 : all faulty aircraft are aged > 12 years except
one small company out of the EU but in the ECAC ( same fault
one regional company with 2 types of turboprops, built in 88 & 93
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A2 - 2
ANNEX
°3
STNA Records of Transponders returned to Maintenance
Table extracted from a Inquiry/report of the STNA / 2RC
" Enquête relative à l'entretien des transpondeurs (records 1994 / report 1995 ) "
The table splits between the 2 possible reasons for return to the workshop.
Problems due to the installation ( connectors, cabling, antenna, humidity, ...) are NOT recorded; this is a major
drawback.
The age of the faulty transponders is often > 20 years.
Frequency problems are partially due to insufficient testing possibilities, the transponder being just verified by SWR.
F1 ⇒ F2 problems are partially due to insufficiencies of the test equipment, the time quantum being too large.
Total XPDRs
Reason for return
qty
55
42
50
147
%
100
100
100
for calibration
qty
%
36
65
29
69
13
22
78
for repair
qty
19
13
37
69
(1)
Failure cause
Frequency ( out XPDR )
(2)
Reply percentage
11
35
7
24
7
19
4
16
Power
( out XPDR )
Sensitivity ( MTL)
(3)
Pulse positions
17
5
39
12
3
27
13
3
26
4
2
13
Pulse width
5
10
7
94
3
7
5
3
4
0
49
2
6
7
45
Category
General Aviation
Business Aviation
Commercial Aviation
Total transponders
Delay time ( P3 ⇒ F1 )
Total Failure
Total transponders
= 64 % of
all
returned
XPDRs
≠ 100
(4)
= 63 % of XPDRs
returned for calibration
%
35
31
74
= 65 % of XPDRs
returned for repair
(1)
The transponders showing other causes of failures are not listed here, having not been requested in the inquiry.
(2)
At PRF = 1200 Hz.
(3)
F1 ⇒ F2 only tested.
(4)
≠ 100 because some transponders present multiple faults.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 3 - 1
1 : Reply Frequency
[140 units]
number of units
25
20
15
10
5
0
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
frequency offset [ <--> 1090 MHz ]
number of units
2:
Reply Percentage @PRF=1200 Hz
[140 units]
70
60
50
40
30
20
10
0
40
50
60
70
80
90
100
percentage
number of units
3:
Transponder Reply Power
[139 units]
10
9
8
7
6
5
4
3
2
1
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
power [ W ]
4:
Transponder Sensitivity
[141 units]
number of units
50
40
30
20
10
0
-80
-79
-78
-77
-76
-75
-74
-73
-72
-71
-70
-69
-68
-67
-66
-65
sensitivity [ dBm ]
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 3 - 2
number of units
5:
80
70
60
50
40
30
20
10
0
20.0
20.2
20.4
Pulse Position F1 --> F2
20.6
20.8
21.0
[140 units]
21.2
21.4
21.6
21.8
22.0
spacing [ us ]
number of units
6:
40
35
30
25
20
15
10
5
0
0.32
0.34
0.36
0.38
0.40
Pulse Width
0.42
0.44
0.46
[140 units]
0.48
0.50
0.52
0.54
0.56
0.58
0.60
0.62
width [ us ]
number of units
7:
16
14
12
10
8
6
4
2
0
2.20
2.30
2.40
2.50
Delay Time ( P3 --> F1 )
2.60
2.70
2.80
2.90
3.00
[130 units]
3.10
3.20
3.30
3.40
3.50
3.60
time [ us ]
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 3 - 3
ANNEX
°4
STNA Notice to Airlines
Au cours du dernier mois, l'attention du STNA a été attirée à plusieurs reprises sur des défauts
d'installations radioélectriques de bord comprenant des ATC Mode S (fausses adresses notamment).
Des enquêtes faites, il ressort qu'en règle générale les dispositions prises pour vérifier la partie Mode S de
l'installation sont insuffisantes.
Je vous transmets en annexe la liste des vérifications qui doivent être faites lors des contrôles périodiques
(tests globaux notamment).
Lorsqu'une intervention sur l'aéronef est susceptible d'affecter le fonctionnement du Mode S, tout ou partie
de ces vérifications sont à effectuer (contrôle de l'adresse Mode S notamment).
Par ailleurs, je vous précise que l'extension du domaine d'activité à l'entretien des aéronefs équipés de
transpondeurs Mode S doit faire l'objet d'un amendement à vos spécifications d'agrément et qu'elle doit être
précédée d'une mise en place des moyens adéquats (formation notamment).
Veuillez agréer, Monsieur le Directeur, l'expression de ma considération distinguée.
EMETTEUR
1) Puissance - fréquence
2) Caractéristique des impulsions en Mode A et C
3) Temps de réponse : Mode A - Mode C - Intermode - Mode S
4) Période squitter.
NOTA : Le cas échéant prendre en compte la diversité d'antenne.
RECEPTEUR
1) Sensibilité Mode A / Mode C / Mode S
2) Vérification SLS et SPR.
DONNEES
1) Adresse Mode S (par rapport à l'immatriculation)
2) Adresse invalide
3) Réponse
DF0 - DF4 - DF5 -
si nécessaire
DF16 - DF20 - DF21 - DF24
4) Vérification des champs
DF11
AA : adresse
RI : vitesse avion cablée
AC : altitude
ID : identification
VS : indication sol / vol
FS : statut de vol plus timers
CA : capabilité
Si l'équipement est interfacé avec TCAS / ADLP … des essais complémentaires doivent être faits.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 4 - 1
ANNEX
°5
Influence of Out-of-norm Characteristics on Radar Data
a]
Jan.uary 1995 : STNA - EEC - Thomson SDC
Author : Jérôme AMANRICH / STNA 4
Object : Report on the French transponder trials
Service Technique de la Navigation Aérienne
13 mars 1995
Département 4
Glossary :
1
Introduction
2
Detection trials
3
Modification of one pulse of the code
4
Transponders frequency change
5
Conclusion
2.1
F1 & F2 alterations
2.2
Only F1 alterations
1 Introduction
In January 1995, in close co-operation with Thomson-CSF/SDC and EEC, STNA performed trials in order to evaluate
the effects of transponders' malfunction on SSR sensor processing. The experimentation was conducted at Orly
experimental station, the technical configuration of which can be regarded as almost the same as the one of the
French operational radars.
antenna AS 809
Transmitter
RSM 970
Digital
oscilloscope
videos
Extractor
ERM 970
replies
Processor
TPR 1000
Recording
PC
plots
Before each test, the pulses' shape and timing were checked on a digital oscilloscope which received video signals
from the receiver's output.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 5 - 1
Service Technique de la Navigation Aérienne
13 mars 1995
Département 4
Two types of data were recorded :
•
The replies representing each transponder's reply received within an antenna sweep. The antenna
revolution period was 8 seconds long and the PRF was set to 125 Hz. With these settings, we received
about 7 replies per scan.
•
The plots are made by the local processing from the replies.
2 Detection Trials
The first trials concerned the detection issues. Therefore we modified the framing pulses' features as the detection
fully depends on F1 and F2 characteristics.
2.1 F1 and F2 alterations
We set F1 and F2 widths at values between 300 ns and 600 ns. Then for each value, we changed F1 - F2 spacing.
F1 - F2 spacing
F1 & F2 width
Replies detected
20.1 µs
20.2 µs
20.3 µs
20.4 µs
20.5 µs
20.1 µs
20.2 µs
20.3 µs
20.4 µs
20.5 µs
20.1 µs
20.2 µs
20.3 µs
20.4 µs
20.5 µs
20.1 µs
20.2 µs
20.3 µs
20.4 µs
20.5 µs
20.1 µs
20.2 µs
20.3 µs
20.4 µs
20.5 µs
300 ns
"
"
"
"
350 ns
"
"
"
"
450 ns
"
"
"
"
550 ns
"
"
"
"
600 ns
"
"
"
"
81 %
62 %
65 %
75 %
81 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
• STFTV •
[ Final Report to SURT ][ May 1995 ]
Plots detected
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
page A 5 - 2
Service Technique de la Navigation Aérienne
13 mars 1995
Département 4
We noticed that the ERM can bear a wide range of F1 - F2 widths and spacing values. This is due to the use of
several extraction criteria: edge to edge or edge to state coincidence criteria which both allow a correct detection.
The harder limitation is the suppression of narrow pulses which occurs at 300 ns width and under. Any pulse thinner
than 240 ns is automatically suppressed. Detection is then impossible.
2.2 Only F1 alteration
The purpose of this experiment was to highlight a problem which occurred in a few transponders. Because of
modulation controls, F1 rising edge is put out of shape and delayed too much. In this part we have kept F2 width
equal to nominal 450 ns.
F1 - F2 spacing
20.1
20.2
20.3
20.4
F1 width
µs
µs
µs
µs
350 ns
"
"
"
20.1 µs
20.3 µs
20.4 µs
290 ns
"
"
replies detected
100
100
100
100
%
%
%
%
40 %
45 %
47 %
plots detected
100
100
100
100
%
%
%
%
64 %
85 %
85 %
In fact, the results are quite the same as the previous ones. We can note the effect of the narrow pulse restriction.
That is why we could not make further tests with narrower F1 pulses.
3
Modification of a pulse of the code
During this trial we have modified both the position and the width of C1 pulse in order to know the effects on
the detection percentage of right code. For this experiment F1 & F2 pulses were nominal (width = 450 ns , spacing =
20.3 µs ). Therefore the detection has been assured without any problem.
The right code detection percentage is lower than 100 % for a pulse with TWO parameters at the limit of the
ICAO norm at the same time. We can explain this result by the fact that the ERM's algorithm is based on the width
coherence between the code pulses and the framing pulses ( all the pulses of a reply are expected to have the same
width ). We also note that the ERM's behaviour is not symmetrical : the results are better near the upper limits ( C1
width = 550 ns ).
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 5 - 3
Service Technique de la Navigation Aérienne
13 mars 1995
Département 4
F1 - F2 spacing
1.300
1.350
1.450
1.550
1.600
1.300
1.350
1.450
1.550
1.600
1.300
1.350
1.450
1.550
1.600
1.300
1.350
1.450
1.550
1.600
4
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
C1 width
Right codes ( ERM output)
300 ns
"
"
"
"
350 ns
"
"
"
"
450 ns
"
"
"
"
550 ns
"
"
"
"
0%
2%
51 %
75 %
41 %
7 %
34 %
100 %
100 %
72 %
65 %
100 %
100 %
100 %
68 %
100 %
100 %
100 %
100 %
69 %
Right codes ( TPR output)
0
0
64
100
62
0
47
100
100
100
88
100
100
100
100
100
100
100
100
100
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
%
Transponder's frequency changes
Frequency
1083
1085
1087
1090
1093
1095
1097
MHz
MHz
MHz
MHz
MHz
MHz
MHz
Replies detected
100
100
100
100
100
100
100
%
%
%
%
%
%
%
Plots detected
100
100
100
100
100
100
100
%
%
%
%
%
%
%
The frequency parameter seems to have no effect on the processing results probably because the receiver's band
width is large enough, about 1090 MHz ± 5 MHz which is more than the ICAO norm (1090 ± 3 MHz). That is why
with these values for the frequency, we were not able to see any difference.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 5 - 4
Service Technique de la Navigation Aérienne
13 mars 1995
Département 4
5
Conclusion
The radar we tested is rather tolerant to large fluctuations of the transponder parameters around the ICAO's
values and quite beyond the ICAO's limits.
Moreover, the tests gave the confirmation that the more efficient an extractor is regarding degarbling, the
less tolerant it is with out-of-norm parameters.
The tests also showed that it was very difficult to forecast the behaviour of the radar when more than two
transponder parameters were not nominal. Some transponders may show complex alterations. It is impossible to test
all the situations.
Last but not not least, it has not been possible to test jitter situations (one or more transponder parameter(s)
change(s) during a reply duration). And yet we know that this problem can occur (especially with the frequency) and
that it can be responsible for serious troubles.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 5 - 5
ANNEX
°6
Influence of Out-of-norm Characteristics on Radar Data
b]
January 1995 : RVA Brussels Airport
Author : Danny DEVOS / RVA - RLW SV / AE / RADAR
Object : Report on the fixed transponder test at the Brussels Airport from 18 to 20 January 1995
1
Scope
A test with a fixed transponder was carried out on the Brussels Airport by EUROCONTROL / EEC and the RVA/RLW
on January 18 to 20, 1995.
The purpose of the test was to assess the influence of some out-of-norm transponder parameters on MSSR radar
performance ( probability of detection and code validation ).
2
Test set-up
A fixed Mode-S transponder of which some Mode A/C characteristics are programmable was used. Plot recordings of
the extractor outputs of two modern MSSR radar of different manufacturers were made.
Both radars are located at the Brussels Airport at a distance of approximately 400 meters from each other. The fixed
transponder was installed on the roof of the control tower which is about 1 NM from the radars. The transponder reply
delay was increased in order to position the plots at a distance of about 40 NM from the radars.
The following transponder parameters were changed :
3
- F1 ⇒ F2 spacing
( ICAO tolerance : 20.300 µs
± 0.100 µs )
- pulse width F1 & F2
( ICAO tolerance :
± 0.100 µs )
- position of C1 pulse
( ICAO tolerance : (n x 1.450) µs ± 0.100 µs )
- C1 pulse width
( ICAO tolerance :
0.450 µs
± 0.100 µs )
- transponder reply frequency
( ICAO tolerance :
1090 MHz
± 1 MHz
0.450 µs
)
Test results
The following tables contain the recording results.
F1 ⇒ F2 spacing : radar A is not very sensitive to out-of-norm spacing. Radar B however is very sensitive to that; the
Pd drops significantly.
F1 & F2 pulse width : radar is more sensitive to pulse width variation than radar B. The detection drops to zero for
radar A as soon as the pulse width deviation from the nominal value is larger than 0.150 µs.
C1 pulse width
: same conclusion as above.
C1 pulse position : both radars show a decrease in Pd. Radar B also shows a pronounced decrease in Mode C
validation.
Reply frequency
4
: the radars are not very sensitive to frequency deviations.
Conclusions
The influence of out-of-norm parameters on the radar data quality is heavily dependent on the radar receiver and
extractor settings.
Some of the out-of-norm values however result in a drastic decrease of the radar performance.
Brussels 14 / 03 / 95 .
RVA / RLW SV / AE / RADAR
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 6 - 1
Results from RADAR A
RVA / RLW Airport Bruxelles National
Table A1 / 2
Test description
Normal operation
F1 ⇒ F2
Blips / scan ratio
Mode A Validation
Mode C Validation
in %
in %
in %
100
100
99
: 20.0 µs
20.1 µs
47
61
97
100
100
100
20.2 µs
100
100
100
20.4 µs
100
100
100
20.5 µs
100
76
100
100
absent C
20.6 µs
20.7 µs
no detection
*
*
20.8 µs
no detection
*
*
9
0
0
20.3 µs
24
83
78
100
83
100
20.4 µs
no detection
*
*
20.5 µs
no detection
*
*
100
100
100
20.2 µs
97
100
100
20.3 µs
100
100
100
20.4 µs
96
99
100
100
45
Pulsewidth 200 ns
F1 ⇒ F2 : 20.3 µs
no detection
*
*
Pulsewidth 150 ns
F1 ⇒ F2 : 20.3 µs
no detection
*
*
Pulsewidth 800 ns
F1 ⇒ F2 : 20.3 µs
3
0
absent C
no detection
*
*
20.4 µs
no detection
*
*
20.5 µs
no detection
*
*
97
90
0
99
100
100
Pulsewidth 300 ns
F1 ⇒ F2 : 20.1 µs
20.2 µs
Pulsewidth 600 ns
F1 ⇒ F2 : 20.1 µs
20.5 µs
Pulsewidth F1 : 200 ns, F2 : 450 ns
F1 ⇒ F2 : 20.3 µs
Pulsewidth F1 : 300 ns, F2 : 450 ns
F1 ⇒ F2 : 20.3 µs
20.4 µs
• STFTV •
[ Final Report to SURT ][ May 1995 ]
absent C
80
page A 6 - 2
Results from RADAR A
RVA / RLW Airport Bruxelles National
Table A2 / 2
Test description
Blips / scan ratio
Mode A Validation
Mode C Validation
in %
in %
in %
This table : all F1 ⇒ F2 : 20.3 µs
& pulse width all F1 & F2 : 450 ns
Position C1 : 1.30 µs after F1
Pulsewidth C1 : 300 ns
no detection
*
*
450 ns
51
100
77
600 ns
99
100
100
Position C1 : 1.45 µs after F1
Pulsewidth C1 : 300 ns
450 ns
32
100
42
100
100
100
600 ns
99
100
100
Position C1 : 1.60 µs after F1
Pulsewidth C1 : 300 ns
89
79
100
450 ns
74
9
100
600 ns
99
100
100
1083 MHz
detection OK
*
*
1097 MHz
detection OK
*
*
1099 MHz
detection OK
*
*
1101 MHz
detection OK
*
*
1103 MHz
POOR detection
*
*
*
*
Frequency
1105 MHz
• STFTV •
NO
detection
[ Final Report to SURT ][ May 1995 ]
page A 6 - 3
Results from RADAR B
RVA / RLW Airport Bruxelles National
Table B1 / 2
Test description
Normal operation
F1 ⇒ F2
Blips / scan ratio
Mode A Validation
Mode C Validation
in %
in %
in %
100
100
98
no detection
*
*
73
100
100
20.2 µs
100
100
100
20.4 µs
100
100
0
20.5 µs
13
no detection
100
*
0
20.6 µs
20.7 µs
no detection
*
*
20.8 µs
no detection
*
*
Pulsewidth 300 ns
F1 ⇒ F2 : 20.1 µs
71
100
100
20.2 µs
100
100
100
20.3 µs
100
100
95
20.4 µs
98
100
0
20.5 µs
6
100
0
73
100
100
20.2 µs
98
100
100
20.3 µs
100
100
100
20.4 µs
97
6
100
100
0
20.5 µs
Pulsewidth 200 ns
F1 ⇒ F2 : 20.3 µs
16
100
100
Pulsewidth 150 ns
F1 ⇒ F2 : 20.3 µs
no detection
*
*
Pulsewidth 800 ns
F1 ⇒ F2 : 20.3 µs
100
100
100
no detection
*
*
20.4 µs
95
100
97
20.5 µs
91
100
100
94
100
100
100
100
100
: 20.0 µs
20.1 µs
Pulsewidth 600 ns
F1 ⇒ F2 : 20.1 µs
Pulsewidth F1 : 200 ns, F2 : 450 ns
F1 ⇒ F2 : 20.3 µs
Pulsewidth F1 : 300 ns, F2 : 450 ns
F1 ⇒ F2 : 20.3 µs
20.4 µs
• STFTV •
[ Final Report to SURT ][ May 1995 ]
*
0
page A 6 - 4
Results from RADAR B
RVA / RLW Airport Bruxelles National
Table B2 / 2
Test description
Blips / scan ratio
Mode A Validation
Mode C Validation
in %
in %
in %
This table : all F1 ⇒ F2 : 20.3 µs
& pulse width all F1 & F2 : 450 ns
Position C1 : 1.30 µs after F1
Pulsewidth C1 : 300 ns
100
100
89
450 ns
100
100
89
600 ns
100
100
95
Position C1 : 1.45 µs after F1
Pulsewidth C1 : 300 ns
450 ns
100
97
100
100
97
97
600 ns
100
100
95
Position C1 : 1.60 µs after F1
Pulsewidth C1 : 300 ns
99
86
100
450 ns
70
100
91
600 ns
48
100
90
1083 MHz
detection OK
*
*
1097 MHz
detection OK
*
*
1099 MHz
detection OK
*
*
1101 MHz
detection OK
*
*
1103 MHz
detection OK
*
*
1105 MHz
NO
*
*
Frequency
• STFTV •
detection
[ Final Report to SURT ][ May 1995 ]
page A 6 - 5
ANNEX
°7
Influence of Out-of-norm Characteristics on Radar Data
b]
March 1995 : DFS at GöTZENHAIN
Introduction
In the following pages are the results of the transponder tests, executed from March 13 to 16.
In spite of some start difficulties, some tests could be executed successfully.
The CPME station was chosen as the sending one.
The transponder codes were 7777 in Mode A and 6062H in Mode C (as for the CPME).
The test transponder could vary its F1, F2 & C1 pulses in width and position. The width variation was done by
modifying the trailing edge of the pulses.
In addition, the frequency could be modified ( TESTS 12 & 13 ). It was only at 1080 and 1100 MHz that no replies at
all were accepted.
To execute the largest amount of tests, the limit of 30 scans was adopted to determine the Pd (probability of
detection).
The results were much " better " (as far as the Pd is concerned) than in Orly. All tests, where the parameters lies
inside the ICAO tolerances, gave a Pd of 100 % , even when 2 or 3 parameters were simultaneously modified
(TESTS 3, 4, 5, 10 & 11 ).
In TEST 3, there were 4 faulty Mode C and probably a garbling in scan 21. TESTS 4 & 6 present 1 faulty Mode C
each.
The largest simulated fault was in TEST 8. The RPC ( see drawing ) did not detect the pulse C1 anymore and output
the code A 7767 ; the true code A 7777 was detected only 5 times, that is, a Pd of 16.66 %.
Synchro
& video
siganls
RPC
Reply
Processor
& Correlator
MSSR TAR
PLOTS
LAN
Ethernet
Bus
DARE
Radar Data
Evaluation
Tool
AS 909
antenna
ICPME 1
antenna
RSM
Interrogator
Receiver
Auxillary
Transmitter
J409
Omega
Envelop
EUROCONTROL
Transponder
ICPME 2
Video
Log Σ
J 302
Scope
LeCroy
Transponder
in test
Printer
HP
Test set-up of TRANSPONDER TEST with EUROCONTROL
GOETZENHAIN RADAR STATION
March 13 to 15, 1995
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 7 - 1
Test Purpose
The purpose of the test was to analyse the effects on the radar of transponders operating at the limits or outside
ICAO requirements.
Test Principles
A transponder slightly modified is used. It is possible to change the width of some pulses, to shift their position and
also to modify the RF frequency of the transponder.
Test Conditions
Antenna rotation period
:
10 seconds
Interrogator PRF :
123 Hz
Interlacing
Staggering
:
ACAC
Receiver SLS
:
ON
:
OFF
STC law
:
0
Test Set-up
+++
The test set-up is described in the above drawing.
The EUROCONTROL transponder has been installed inside the house located nearby the tower housing
both ICPMEs (Test transponders part of the radar). It was connected to the antenna of one of the ICPMEs,
the nº 2.. The other ICPME was also operating and used for verification.
( ICPME : International Calibration Performance Monitor Equipment ).
+++
Two different types of Data Recordings were performed for each test :
+ Video recording : The video LOG
Σ
(output of J302 of receiver) corresponding to the replies of the
transponder under observation is visualised by means of a digital scope LeCroy and recorded by hard copy
to a IEEE compatible HP Thinkjet printer.
Before proceeding to the next step, all the timing parameters (width, shifting) are carefully verified.
+ Probability of detection performed on 30 turns with DARE evaluation tool equipment : the plots output by
the RPC on the LAN (Ethernet bus) are recorded by DARE and the presence of the plot corresponding to
the transponder under observation is verified at each turn. A listing giving the Range, Azimuth, Mode A,
Mode C and the number of the turn of the corresponding plot is printed for each test.
Test Cases & Results
Case
F1-F2
C1 width
C1 position
Pd
1
nominal
nominal
nominal
100
%
2
20.2 µs
"
"
100
%
3
20.2 µs
minus 100 ns
"
100
%
4
20.2 µs
nominal
<--- 100 ns
100
%
5
20.2 µs
minus 100 ns
<--- 100 ns
100
%
6
20.3 µs
minus 200 ns
nominal
100
%
7
20.3 µs
nominal
<--- 200 ns
90
%
8
20.3 µs
minus 200 ns
<--- 200 ns
93.33 %
9
20.3 µs
minus 100 ns
nominal
10
20.3 µs
plus 100 ns
200 ns --->
100
%
11
20.2 µs
nominal
100
%
12
RF Frequency
1093 MHz
1085 MHz
nominal
100
%
nominal
100
%
13
• STFTV •
F1 width :
minus 100 ns
nominal
nominal
[ Final Report to SURT ][ May 1995 ]
96.7 %
page A 7 - 2
ANNEX
°8
Influence of Out-of-norm Characteristics on Radar Data : Combined Results
( of Annexes 5, 6 & 7 )
Remark : In all 4 tables, all figures are percentages, except the first columns ( width, spacing & frequencies).
1
F1 F2 width & spacing variation vs. rest of pulses
F1 F2
ORLY
width spacing replies plots
ns
µs
BRUSSELS A
blips
Mode A Mode C
/scan
BRUSSELS B
GOTZENHAIN
blips
Mode A Mode C Probability
/scan
of detection
150
20.3
.
.
.
.
no det
/
/
no det
/
/
200
20.3
.
.
.
.
no det
/
/
16
100
100
300
20.1
20.2
20.3
20.4
20.5
81
62
65
75
81
100
100
100
100
100
9
24
83
no det
no det
0
78
100
/
/
0
83
100
/
/
71
100
100
98
6
100
100
100
100
100
100
100
95
0
0
350
20.1
20.2
20.3
20.4
20.5
100
100
100
100
100
100
100
100
100
100
450
20.0
20.1
20.2
20.3
20.4
20.5
20.6
20.7
20.8
.
.
100
100
100
100
100
.
.
.
.
.
.
.
.
100
100
100
100
100
.
.
.
.
.
.
47
100
100
100
100
100
76
no det
no det
61
100
100
100
100
100
100
/
/
97
100
100
99
100
absent
absent
/
/
no det
73
100
100
100
13
no det
no det
no det
/
100
100
100
100
100
/
/
/
/
100
100
98
0
0
/
/
/
550
20.1
20.2
20.3
20.4
20.5
100
100
100
100
100
100
100
100
100
100
600
20.1
20.2
20.3
20.4
20.5
100
100
100
100
100
100
100
100
100
100
100
97
100
96
99
100
100
100
100
100
100
100
100
45
80
73
98
100
97
6
100
100
100
100
100
100
100
100
0
0
800
20.3
.
3
0
absent
100
100
100
.
.
.
100
100
Width: nominal value 450 ns ± 100 ns / Spacing : F1 ⇒ F2 , nominal value 20.3 µs ± 0.10 µs
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 8 - 1
2
Pulse C1 width & spacing variation vs. rest of pulses
C1
ORLY
BRUSSELS A
width spacing replies
ns
µs
plots
blips
/scan
250
1.25
1.45
.
.
.
.
300
1.30
1.35
1.45
1.55
1.60
0
2
51
75
41
0
0
64
100
62
1.30
1.35
1.45
1.55
1.60
7
34
100
100
72
0
47
100
100
100
1.25
1.30
1.35
1.45
1.55
1.60
.
65
100
100
100
68
88
100
100
100
100
1.30
1.35
1.45
1.55
1.60
100
100
100
100
69
100
100
100
100
100
1.30
1.45
1.60
.
.
.
350
450
550
600
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
blips
/scan
.
.
.
.
Mode A Mode C Probability
of detection
.
.
.
.
.
.
.
.
/
/
100
100
89
32
42
100
100
100
97
89
79
100
99
86
100
.
.
.
.
.
.
.
100
.
100
.
.
100
74
9
.
.
.
.
.
.
.
51
.
.
.
.
.
Mode A Mode C
GOTZENHAIN
no det
.
.
.
BRUSSELS B
.
.
.
.
99
99
87
.
.
100
100
75
.
.
.
.
.
.
100
.
.
100
.
.
97
100
70
77
.
.
.
.
.
100
100
100
.
.
.
.
100
100
48
.
.
F1 - F2 = 20.2 µs >
F1 - F2 = 20.2 µs >
.
.
100
.
.
100
97
100
91
.
.
100
100
100
100
100 (3)
90
89
F1 - F2 = 20.2 µs >
.
.
93.4 (1)
100 (2)
.
.
.
.
100 (2)
96.7
100
95
95
90
Width: nominal value 450 ns ± 100 ns.
Spacing : from F1 , nominal value 1.45 µs ± 0.10 µs
(1)
Correct codes in MODE C : 17 %
(2)
"
"
"
: 97 %
(3)
"
"
"
: 87 %
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 8 - 2
3
F1 width & spacing variation vs. rest of pulses
F1
ORLY
BRUSSELS A
BRUSSELS B
width spacing replies
ns
µs
plots
blips
/scan
200
20.3
20.4
20.5
.
.
.
no det
no det
no det
/
/
/
/
/
/
no det
95
91
/
100
100
/
97
100
290
or 300
20.1
20.2
20.3
20.4
40
64
45
47
85
85
97
99
90
100
0
100
94
100
100
100
100
100
20.1
20.2
20.3
20.4
100
100
100
100
100
100
100
100
20.3
100
100
350
450
.
.
.
.
.
.
.
.
.
.
.
100
Width: nominal value 450 ns ± 100 ns /
4
.
Mode A Mode C
.
.
100
.
blips
/scan
GOTZENHAIN
.
100
Mode A Mode C Probability
of detection
.
.
100
.
.
100
.
100
100
100
Spacing : from F2 , nominal value 20.3 µs ± 0.10 µs.
Frequency variation
F1
ORLY
BRUSSELS A
BRUSSELS B
MHz
replies
plots
blips
/scan
1080
1081
1083
1085
1087
1090
1093
1095
1097
1099
1100
1101
1103
1105
.
.
.
.
100
100
100
100
100
100
100
.
.
.
.
.
.
.
.
.
.
.
.
.
.
100
100
100
100
100
100
100
.
.
.
.
.
.
.
.
.
.
.
.
.
.
no det
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
100
.
.
.
100
.
.
100
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
OK
OK
.
.
OK
poor det
no det
Mode A
/
Mode C
/
blips
/scan
.
.
Mode A
GOTZENHAIN
Mode C
Probability
of detection
.
.
.
.
.
.
.
.
.
.
0
>0
.
.
.
.
.
100
100
.
.
.
100
.
.
100
.
100
100
.
.
.
.
.
.
.
.
>0
0
OK
.
OK
OK
.
.
OK
OK
no det
/
/
Nominal value: 1090 MHz ± 3 MHz.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 8 - 3
ANNEX
°9
Transponder Proportions in ECAC States
total number
Mode S
Classic TP
of
aircraft
known
known
with TP
cavity type
solid st.ate
11801
616
25438
1328
in % of equipped aircraft
90.6 %
id, minimum
id, maximum
usable total
weighed total
28483
Σ
26766
1302
4.7 %
95.4 %
4.6 %
29.4 %
0
47.1 %
0
100 %
67.2 %
100 %
52.9 %
mean
%
minimum
100
maximum
90
80
70
60
50
40
30
20
10
0
Classic, cavity
• STFTV •
Classic, solid state
[ Final Report to SURT ][ May 1995 ]
Mode S
page A 9 - 1
ANNEX
°10
Maintenance Requirements in each Country
A10.1 Maintenance rules FAA 91.413 / part 43 / app. F
( These regulations are called hereafter FAR43 ).
With the required periodicity ( 24 months maximum between
RAMP TESTS
), the FAR 43 requires the following list of
tests to be executed :
a) Reply Frequency
Fq
1090 MHz ± 3 { 1090 MHz ± 1 , if the XPDR is Mode S }
b) Suppression pulse
Sr
for P2 = P1
c) Sensitivity (MTL)
Mt
, less than 1 % reply
for P2 = P1 - 9 dB , more than 90 % reply
∆M
d) Power
Pw
= -73 dBm ± 4 { -74 ± 3 dBm , if the XPDR is Mode S }
≤ 1 dB between the MTL in Mode A & Mode C
> 51 dBm , < 57 dBm { 48.5 dBm for a/c under 15000 ft or low speed}
e) for Mode S XPDRS only :
- if diversity is installed, power difference between selected antenna <-> other antenna is > 20 dB
- the XPDR replies to its own address only ( try this address and two other ones ).
- send UF 4
--> correct DF 4 or 5, with altitude bits = Mode C and code bits = Mode A bits;
id. with UF 20, 21 & 24, if this possibility is installed.
- send an All-call UF 11 --> DF 11 with correct address & capability
- Mode A•C only All-call --> should not reply
- squitter is ± 1 / s
A10.2 List of the Maintenance Requirements per Country
see next pages, where the following abbreviations are used
Al
=
Pressure Altimeter
Co
=
Code verification in both modes, including SPI pulse
Fq
=
Reply Frequency
Mt
=
Sensitivity or Minimum Trigger Level
(∆M =
Pp
=
(Ff =
Pw
difference of MTL between Mode A and C)
All Pulses position offset
F1 to F2 only spacing )
=
reply Power
Rd
=
Rise and decay times of the average pulse
Sr
=
SLS vs. P1 / P2 ratio
Ss
=
SLS Vs P1 ⇒ P2 spacing
Wi
=
Pulse width
(W2 =
%
=
Width of F2 pulse only)
% of reply at current PRF
Note : GA = General Aviation / AL = Commercial Airlines
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 10- 1
COUNTRY
Max.
interval
RAMP TESTS
interval
test list
BENCH TESTS
with
interval
AT
(Austria)
AL : 24 m
GA : 12 m
FAR 43
BE
(Belgium)
GA --> GA : 12 m
AL : OC
FAR43
+Al
ATC 601
GA: 24 m
BG
(Bulgaria)
(AC) test list
with
= RAMP tests
+ digital
encoders
ATC 1400A
not
required
1800 h
300 h
Pw, Mt, Co,
Pp, Wi,..
ATC 2000 ?
900 h
CH
(Switzerland)
24 m
24m
FAR 43
ATC 600A
ATC 601
not
required
( If done :
FAR43)
ATC 1200Y3
ATC 601
TIC T50
DE
(Germany)
12 m
12 m
FAR 43
+W2, Ff
ATC 600, 600A
ITT .....
24 m
maint.manual
ATC 1200Y
ATC 1300Y
Collins, Bendix
DK
(Danemark)
no time
no time
maint.manual
ATC 1200Y3
ATC 1400, ..C
EI
IFR : 24
m
24m
maint.manual
not listed
(Ireland)
FR , MC
(France +
Monaco)
GB
(United
Kingdom)
HU
(Hungary)
Pw, Mt, Fq, ATC 600, 600A after repair
Sr, As,
Liniaire LX-3B or overhaul
FAR43
not listed
after repair
12 m
1 yr (IFR)
3 yrs (VFR)
?
3 yrs (IFR)
6 yrs
(VFR)
?
OC
24 m
FAR43
ATC 600, 601
Mode S : NOT
selftest
=FAR43
+ Al, SPI
KASZO
12.5 m
maint.manual
24 m
Tupolev
ATC 1400
+ scope
by m.m
OC
Occidental
as req
= RAMP tests
+ Sr, Ss, Rd, %
12 m
ATC1400
+ scope &
multimeter
IE
(Ireland)
24 m
notice A39
after repair
= FAR 43
ATC 600, 600A
TIL T49C
TCAS 201
OC
or after
repair
= FAR43
ATC 1400A
Bendix
IS
(Iceland)
24 m
12 or 24 m
or maint.
manual
Co, Ff, Fq,
Pw, Sr, Ss
ATC 600A
ATC 601
id ramp
id ramp
ATC 1200Y3
ATC 601
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 10- 2
COUNTRY
Max.
IT
(Italy)
RAMP TESTS
interval
interval
test list
with
interval
(AC) test list
with
funct.only :
12 m
or as req
by m.m
FAR 43
& maint.
manual
ATC 600A
& others
not
required
maint. man.
ATC 600A
20±2 days
Built-in
not
if done :
ATC 600, 600A
required
Al, Co, Fq,
Mt, Pw
KASSO-I, -V,
KASSO ML
JMO-65M
24 m
maint. man.
ATC 1200
12 m
all : 24 m
LT
(Lithuania)
LU
(Luxemburg)
BENCH TESTS
24 m
ATC 600, 600A
test module KASSO-I, -V,ML
12 m
ATC 600, 600A
Collins 476x3
KURTON sq. N
TIC T48
NL
AL :
OC
OC
maint. man.
OC
maint. man.
(Netherlands)
GA : 24 m
NO
(Norway)
25 m
" "
every
all of
snag
ATC600
" "
ATC 600
every shop
all possible
IRIS 2000
visit after
maint. man.
rectification
PT
(Portugal)
24 m
OC
snag rectif
FAR 43
as req. in
maint.manual
ATC 600
TIC
OC
ATC 1400
IRIS 2000
Squak Naut
maint. man.
ATC 1200Y3
ATC 1400Y
Collins, Bendix
SE
(Sweden)
no
OC
?
?
OC
?
?
SK
(Slovakia)
12 m
as req
by m.m
maint. man.
ATC 600A
NAV402,
MIM69
as req
by m.m &
after repair
maint. man.
ATC 1200
R&S
SMDA or U
SL
(Slovenia)
24 m
OC
maint. man.
ATC 600A
OC
Notes :
1] ATC600 & 600A are for Modes A*C only, ATC601 for Modes A,C & S
TCAS 201 is an extension to ATC601 to cope with some TCAS measurements
" as req. by mm " : as required by the maintenance manual
2] No data from other ECAC countries.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 10- 3
A10.3 Summary
In many countries the maintenance requirements are not split in the same way depending on the type of
aircraft: On Condition, fixed periodicity, list of tests, etc... But a rough summary of the 21 countries listed
(Monaco being grouped with France) is presented here:
Α10.3.1 Tests to be executed
7.5 / 21 ( 35
% ) strict FAR 43 regulations (0.5 counts for either GA or AL)
2 / 21 ( 9.5 % ) FAR 43 + a few tests
3.5 / 21 (16.5 % ) give a list of tests
6 / 21 (28.5 % ) ask to follow the maintenance manuals or On Condition
but 13 / 21 ask for either FAR43 or maintenance manual ATC600 possibilities or both; considering that the
maintenance manual is at least as "demanding" as the FAR43, and taking into account the fact that the
ATC600 has been built to satisfy the FAR43 regulations. One can say that, roughly,
2/3
of the countries apply the FAR43 rules de - facto;
the other countries impose either the maintenance manual obligations alone or a short list of parameters,
like pulse position, pulse width, code integrity, altimeter data, or mode acceptance limits.
Α10.3.2 Periodicity of the RAMP TESTS
7.5 / 21 ( 35 % )
1 year
( or less,
0.5 counts for GA or AL )
9.5 / 21 ( 45 % )
2 years
( sometimes limited to IFR,
"
1
/ 21 (
variable
3
/ 21 ( 14 % )
5 %)
"
"
)
no limit of time.
So, the
4 / 5 of the countries apply a periodicity of
and, out of them,
1/3
"
"
"
"
"
<= 24 months
= 12 months.
Α10.3.3 BENCH TESTS
Most often, bench test are not required, unless after repair, overhaul or declaration of unsatisfactory
replies issued by ATC controllers.
In some countries the bench test is an imposed part of the On Condition maintenance procedure, or for
some types of XPDRs, that are subject to more disfunctions.
Four countries only ask for a bench test with a defined periodicity ( 2 or 3 years or 900 hours)
Α10.3.4 Equipment Used for RAMP TESTS ( here Mode A*C only)
5 / 21 not defined or defined by the On Condition arrangement with the companies.
14 / 21 IFR 600, 600A or equivalent
other equipments are defined but in small quantities each.
So, if any action like automation of a test set would be taken, it should be based on the ATC600 or similar
equipment.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A 10- 4
ANNEX
°11
List of Parameters and Testset Possibilities
PARAMETERS
tests possible with
active or passive tests [1] ↓
Interrogation frequency
acceptance
Reply frequency
( ± 1090 MHz )
Reply power
XPDR dynamic range
( % curve)
MTL
in Modes A & C
∆ MTL
between Modes A & C
Reply pulses positions
Reply pulses width
(Y) [2]
P
Y
(± 50KHz)
Y
Y
(± 0.3MHz)
P
Y
(± 3dB)
A
Y
XXX
X
Y
Y
XXX
X
x
Y
Y
XXX
X
A
Y
Y
Y
Y
XXX
X
P
F1 & F2
(± 500ns)
F1 & F2
(± 50ns)
F1 & F2
(± 50ns)
Y
XXX
X
( all p.)
X
( all p.)
P
SLS vs. P1 ⇒ P2 spacing
A
SLS
A
• STFTV •
Y
Y
A
(all pulses)
Y
XX
(all pulses)
x
x
Y
(±1µs)
A
A
Y
Y
( 0 & -9dB)
X
(Y) [2]
Y
XX
(X) [4]
(Y) [2]
Y
X
(X) [4]
Y
( 0 & -9dB)
Y (0
& -9dB)
XX
X(0&
-9dB)
XX
x
P
Added
in
Bench
X
Y
P
Dead time
( after a normal reply )
Suppression time
( after SLS pulse pair)
Reply rate
@ PRF xxx
Reply rate
@ multiple PRF
Code validity
in Modes A & C
xx
Y
Pulses amplitude variation
within a reply
Mode acceptance
vs. P1 ⇒ P3 spacing
Mode acceptance
vs. P1 & P3 duration
SLS
vs. P1 / P2 ratio
( P3 ⇒ F1 )
ATC1400
/1403
Suitable
for
Ramp
A
P
Delay time
ATC601
A
Pulses rise & decay times
vs. P2 duration
ATC600A
FAR 43 Importance
[3]
Y
XXX
X ( +3 >
-12dB)
X
X
X
A
X
X
A
X
X
P
Y
235 Hz
A
P
Y
Y
235 Hz
(Y) [2]
Y
[ Final Report to SURT ][ May 1995 ]
Y
235 Hz
Y
X
500 Hz
X
x
X
500 Hz
X
X
page A11 - 1
PARAMETERS
tests possible with
active or passive tests [1] ↓
Mode S ADDITIONS
ATC600A
ATC601
ATC1400
/1403
Y
Y
Y
FAR 43 Importance
[3]
Suitable
for
Ramp
Added
in
Bench
no mode S
capability
MTL in Mode S
Reply pulses positions
Reply pulses width
Pulses amplitude variation
within a reply
Delay time
( SPR ⇒ reply preamble )
Synch phase reversal (SPR)
A
P
P
P
Y
P
Formats UF 4, 5, 20, 21, 24
"
All Call
"
Mode A*C only
"
UF 10, 11...
⇒ add , code
"
UF 20, 21...
⇒ contents
Squitter
Diversity : power difference
XXX
XX
XX
x
X
Y
xx
X
A
ON-OFF
xx
A
A
A
A
Y
Y
Y
Y
(X) [4]
X
X
X
X
A
Y
P
P
Y
Y
Y
Y
Y
Y
Y
X
X
X
X
X
X
XXX
XXX
XXX
XXX
X
X
X
xx
X
XX
xx
X
X
Notes
[1]
Active test : where the interrogation has to vary for receiving different replies and reply %
Passive test : the interrogations are strictly nominal ( ICAO standard).
[2]
An extension to the IFR ATC601 exists for TCAS purpose (TCAS-201); and, in this extension, as a subset
of its added capabilities, the following variations are possible:
the interrogation frequency ,
the interrogation rate,
the spacing between pulses P1 ⇒ P3 ( as well as P1 ⇒ P4),
the width of pulses P1 & P3,
thereby executing the tests marked ( Y ) in the IFR601 column.
[3]
When located in the center, the importance follow amount of faults observed in the measurements and
records;
when on the right hand and lower case, it is based on logically computed consequences.
See more details in § 5.4 of the main report.
[4]
When made available with an extension or a renewed Ramp Testset.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A11 - 2
ANNEX
°12
I.F.R. Testset Automation
A12.1 Generalities
With the end of the DATAS project at the EEC and following the request for a Mode S protocol testset, the
EEC decided to evaluate existing testsets. The need to certify the experimental Mode S chain in aircraft
came along with the first conclusions of the STFTV group: they prompted the EEC to make various
evaluations using IFR testset.
The choice of this equipment follows collected information regarding the XPDR maintenance over all ECAC
countries; indeed, it is by far the most used equipment for XPDR testing. Of course, this has no implication
about the future in test equipment developments.
The evaluation was made with an IFR ATC 1400A coupled with the ATC 1403C , both BENCH Testsets.
Other tests are being prepared with the IFR RAMP Testset ATC 601.
Three approaches were chosen:
• 1 The first concerns only Mode A*C tests on ATC1400A . The aim is to develop software tools to
automate a maximum of complete test.
• 2 The second deals with the use of ATC 1400A and 1403C , for Mode S procedures. The aim is the same
as for Mode A*C but it adds an automatic test for various Mode S protocols.
• 3 The third approach will be similar to the first one, but deals with the ATC 601 unit, in order to envisage
the possibility of producing a version of this unit that could i.a. be really controlled by a PC.
We have now results for the first approach and, partially, for the second one.
A12.2 IFR Test Bench Evaluation
A12.2.1 Automatic tests with the ATC1400
For these tests an ATC1400 and a PC are used. An RS232 link controls the bench through a GPIB
interface. The programme is developed under QUICK BASIC; with many subroutines for each different test.
The bench needs specific macro commands. When a sequence of test is terminated, the results are
recorded on disk files. This file is analysed and processed for presentation using EXCEL.
An example is given at the end of this Annex.
The following tests are executed in a sequence :
P1 & P3 Pulse width acceptance
in Mode A
P1 ⇒ P3 spacing acceptance
"
SLS vs. P1 / P2 ratio
"
SLS vs. P1 ⇒ P2 spacing
"
Dynamic range
"
Reply delay ( P3 ⇒ F1)
"
Frequency acceptance ( ± 1030 MHz)
All the same tests
"
in Mode C
Reply percentage vs. PRF
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A12 - 1
These tests last about 30 minutes. However, they are not complete.
Unfortunately, it is not possible to measure automatically the width and the position of each pulse in the
reply.
A12.2.2 Automatic Mode S tests with the ATC1403C
With the same software, it is possible to verify the Mode S electrical characteristics. But first of all we try to
control the Mode S procedures. The initial results are encouraging.
For example, in the same test it is possible to extract the address of the XPDR and to use this data
immediately in the next interrogation.
The COMM A & COMM B procedures described in the following pages were simulated by software. Next,
we send 15 or 16 UPLINK COMM C messages and the same thing for DOWNLINK. These tests were made
manually and will be done by software soon (expected current 1995).
A12.2.3 Automatic tests with the ATC 601
RAMP TESTS in Mode A*C*S are made by this equipment. This testset sends several interrogations in each
mode. The replies are presented on a small digital display ( 6 lines). Either a complete sequence can be
executed, with the general answer (test) PASSED or FAILED, or individual test can be executed individually,
with a bit more explicit data. But the complete test sequence cannot be modified neither the pattern of
interrogations. The results can be printed on a printer through a RS232 line (just printing what was on the
display, nothing more).
IFR representatives in France accept to supply the EEC with a new PROM for this equipment, but the green
light from IFR management ( in the USA) isn't yet arrived.
If obtained, this new PROM could allow through PC control,
•
to change the sequence
•
to modify the format
•
to display data on a PC display ( curves ? )
These tests are hopefully expected current 1995.
A12.3 MODE S Protocol validation
A12.3.1 Airborne Mode S chain validation
Today, there is no complete RAMP TESTSET available that can validate nor certify the Airborne Datalink
Mode S chain. The few tests made with a specific testset are very seldom. Whilst waiting for a certification
bench, the EEC tried using the IFR testset ATC 1400A and 1403C.
One test was successfully made in a A310 at Charles-de-Gaulle airport in March 1994. The conclusion was
that the complete airborne Mode S chain test is possible but the check is made within the limits of the bench
performance., the main limitation being the sensitivity of the bench receiver.
This tool can be used for the airborne Mode S chain validation during the experimental phase but is not
recommended for an operational use.
For two months, the EEC tried to automate the IFR testset. No problem had been met in the Mode A*C, the
first results in Mode S are very interesting and encouraging for procedures.
A12.3.2 Installation
The bench is installed in a vehicle. The antenna is connected to the 1403C testset. The antenna, fixed on a
tripod, is placed close to the aircraft antenna ( maxi. 0.40 m )The cable between the bench and the antenna
should be kept to less than 3 meters.
After verifying the link by a Mode A*C or SQUITTER communication ( results displayed on the bench), some
squitter interrogations are programmed. Then, an interrogation sequence is built ( 16 sequences out of
which the 9 first are already programmed).
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A12 - 2
A12.3.3 Procedure verification
The address is extracted from the first UF11 and used for the following
Then, different procedures are validated :
COMM A transactions are validated by specific messages addressed to the cockpit printer.
COMM B extraction are validated by
•
GICB data input to the system by the DLPU
•
AICB data are detected, the message contained extracted, the message cancelled.
COMM C transactions are not easy ( manually); it is executed with the ELM COMM C of 15 or 16
segments
COMM D transactions of 1 segment can be read by the display; more than one is not possible. A solution to
this is to use 1 COMM C to extract each COMM D segment. But it is very long to prepare and it is
preferable towait for an automatically programmed solution.
IFR - testset : Hardware Setup ( Mode A-C & Intermodes only )
EUROCONTROL
PC
S 1403C
display
ATC 1400A
GPIB - NSIII
IEEE 488
GEN
XMTR
RF-out
Scope
Interrogation
Reply
7777
Control
Box
Presently using:
National Instruments GPIB - PC III
under MS-DOS &
Quick Basic
( but could be run under any
other system )
• STFTV •
[ Final Report to SURT ][ May 1995 ]
DUT
(XPDR)
115 V 400 Hz
Power Supply
page A12 - 3
TRANSPONDER VERIFICATION
EUROCONTROL
IFR Test Bench
TESTS
DATE
OPERATOR
FILE
OCT. 17, 1994
EEC BRETIGNY
zzz.dat
TRANSPONDER CHARACTERISTICS
COMPANY
AIR XXX
TRANSPONDER TYPE
TSxxxxx
SERIAL NUMBER
1050
MANUFACTURER
YYY
MODE A
MODE C
Power
304 W
310 W
Frequency
1090.08 MHz
1090.08 MHz
Code
7777 Code
0 altitude
Delay
3.15 µs
3.17 µs
Jitter
70 ns
50 ns
Reply %
100
100
MTL
-73 dB
-72 dB
no
no
Comments
page 1 of 5
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A12 - 4
Company :
AIR XXX
XPDR type :
YYY
Serial #
1050
Date :
17 -oct-1994
:
1:
Pulse Width Acceptance , Mode A
100
reply %
80
60
40
20
0
0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
P1 & P3 ( us )
2:
Pulse Spacing Acceptance , Mode A
100
reply %
80
60
40
20
0
6.8
7
7.2
7.4
7.6
7.8
8
8.2
8.4
8.6
8.8
9
9.2
P1 to P3 ( us )
3:
SLS Ratio , Mode A
100
reply %
80
60
40
20
0
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
P2 / P1 ( dB )
4:
SLS Spacing , Mode A
100
reply %
80
60
40
20
0
1.3
1.5
1.7
1.9
2.1
2.3
2.5
2.7
P1 to P2 ( us )
page 2 of 5
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A12 - 5
Company :
AIR XXX
XPDR type :
YYY
Serial #
1050
Date :
17 -oct-1994
:
5:
Dynamic Range , Mode A
% of reply
100
80
60
40
20
0
-20
-24
-28
-32
-36
-40
-44
-48
-52
-56
-60
-64
-68
-72
-76
-80
-64
-68
-72
-76
-80
RF level ( dBm )
6:
Reply Delay , Mode A
delay ( us )
3.5
3.3
3.1
2.9
2.7
2.5
-20
-24
-28
-32
-36
-40
-44
-48
-52
-56
-60
RF level ( dBm )
7:
Frequency Variation , Mode A
100
reply %
80
60
40
20
0
1020
1022
1024
1026
1028
1030
1032
1034
1036
1038
1040
frequency ( MHz )
8:
PRF
100
reply %
80
60
40
20
0
100
300
500
700
900
1100
1300
1500
1700
1900
2100
2300
2500
2700
interrogation / s
page 3 of 5
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A12 - 6
Company :
AIR XXX
XPDR type :
YYY
Serial #
1050
Date :
17 -oct-1994
:
9:
Pulse Width Acceptance , Mode C
100
reply %
80
60
40
20
0
0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
P1 & P3 ( us )
10 :
Pulse Spacing Acceptance , Mode C
100
reply %
80
60
40
20
0
18.8
19
19.2
19.4
19.6
19.8
20
20.2
20.4
20.6
20.8
21
21.2
P1 to P3 ( us )
11 :
SLS Ratio , Mode C
100
reply %
80
60
40
20
0
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
P2 / P1 ( dB )
12 :
SLS Spacing , Mode C
100
reply %
80
60
40
20
0
1.3
1.5
1.7
1.9
2.1
2.3
2.5
2.7
P1 to P2 ( us )
page 4 of 5
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A12 - 7
Company :
AIR XXX
XPDR type :
YYY
Serial #
1050
Date :
17 -oct-1994
:
13 :
Dynamic Range , Mode C
% of reply
100
80
60
40
20
0
-20
-24
-28
-32
-36
-40
-44
-48
-52
-56
-60
-64
-68
-72
-76
-80
-64
-68
-72
-76
-80
RF level ( dBm )
14 :
Reply Delay , Mode C
delay ( us )
3.5
3.3
3.1
2.9
2.7
2.5
-20
-24
-28
-32
-36
-40
-44
-48
-52
-56
-60
RF level ( dBm )
15 :
Frequency Variation , Mode C
100
reply %
80
60
40
20
0
1020
1022
1024
1026
1028
1030
1032
1034
1036
1038
1040
frequency ( MHz )
page 5 of 5
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A12 - 8
ANNEX
°13
Detection of Out-of-norm Transponders by the SSR
( including the use of Multi - Radar)
Author :
Gilles RAT (STNA 4)
Contents :
1
2
Out-of-norm transponder detection by the SSR radar.
1. I
Introduction
1. II
Context
1. III
Basic idea
1. IV
Advantages and limitations of the system
1. V
Variant
1. VI
Details to solve, difficulties, etc
1. VII
System extensions
1.VIII
Conclusion
Use of the Multi-radar for the detection of out-of-norm transponders
2. I
Introduction
2. II
Definition of the airspace affected by the new function
2. III
Basic principles
2. IV
Details to solve
2. V
Conclusion
1
Out - of - nor m tr a ns ponde r de te c tion by the SSR
1.1
Introduction
The aim of this document is to propose to the STFTV Group a track to integrate in the SSR radar station a
transponder surveillance system.
Through such a system, all populations of transponders that may be observed would be permanently
controlled and an alert sent in case of failure detected.
These systems would not suffer the same limitations and drawbacks as those of the GTVS.
1.2
Context
A series of recent trials did demonstrate that SSR monopulse radar could be relatively tolerant regarding
transponders whose characteristics lie at the limits of the ICAO norms. However, this tolerance is reduced
compared to SSR sliding window radar, and this reduction towards strict ICAO limits is further increasing in
the next interrogators.
The DATAS measurement campaigns executed till 1993 showed a percentage of out-of-norm transponders
of about 5 %. A recent STNA inquiry on the status of transponders returned to maintenance workshop for
repair or overhaul showed a wide disparity of the various parameters. In any case, the old generation of
transponders present regular drift of parameters.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A13 - 1
1. 3
Basic Idea
The idea would consist of adding in the monopulse interrogators a extra processing chain at the output of
the receiver upper stage, in parallel to the operational chain ( that is generally already duplicated because
of data availability).
This special chain would deliver tracked plots just like the operational chain. These plots would be extracted
through a more " severe" chain, that is, the settings would be strictly adjusted to the ICAO norms.
Plots coming out of this special chain would be compared to those of the normal chain. In case of miss in
the special chain, on would set a " dubious transponder " field in the final plot data at the output of the radar.
This format could be the ASTERIX format. of course, it would be safe before declaring a transponder "
dubious " to wait for n antenna turns, n being determined by experimentation.
Present monopulse interrogator may be described in the following manner:
RECEIVER
( x2)
EXTRACTOR ( x 2 )
TRACKER ( x 2 )
DISPATCH
ASTERIX formatted PLOTS
It would be modified as follows
RECEIVER
( x2)
EXTRACTOR ( x 2 )
TRACKER ( x 2 )
COMPARATOR
DISPATCH
" STRICT " EXTRACTOR
NORMAL TRACKER
" Dubious XPDR " field
in the ASTERIX format
if N successive misses
ASTERIX formatted PLOTS
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A13 - 2
The detection relies on the fact that the out-of-norm XPDR passes through the filter of the Normal way and
is rejected by the More Severe filter of the special extraction.
1.4
Advantages and limitations of the system
Such a system can alert the controllers of potential problems caused by their plots that are still displayed.
The precise diagnostic of the failure is of course not given by such a system. It would necessitate a much
larger modification of the monopulse interrogator. It can probably be avoided if the system is only devoted to
the surveillance of XPDRs in view of the safety of the air navigation, and is not built as a supplementary tool
for XPDR maintenance.
The detection principle requires to be out of garbling situations. Besides, this detection does only apply to
pulse form and position in the XPDR reply.
The main advantage of the proposed system relies on the relatively reduced modifications necessary to be
applied to the present monopulse interrogator.
1.5
Variant
A possible variant is to execute the specific process (hardened extraction, comparator) directly by a modified
version of the existing extraction functions, by applying in parallel a second set of filtering parameters.
In case of detection of an out-of-norm XPDR, the corresponding presence's carry automatically to the rest of
the process the adequate information, finally transmitted to the controller.
This variant would probably need important modifications of the extractors (definition of a new extraction
element).
1.6
Details to solve, difficulties, ...
One must correctly adapt the parameters of the " hardened extractor " to the ICAO tolerances. This setting
depends on the qualification of the initial extractor manufacturer.
Not all the XPDR parameters can be controlled through this " hardened" extraction filtering. But the most
frequent failures, as listed in the recent STNA inquiry, would probably be detected.
Even if the achievement of the above described system does not call into question the present monopulse
extractors, its implementation will need a study & development phase, to be executed by the radar
development manufacturers. Next will come a retrofit of the existing installations. The problem lies in the
time scale, because of:
• the replacement of old classical XPDRs, during the next 10 years ( ? ) , by Mode S units,
• the replacement of classical monopulse interrogators by Mode S adapted versions,
at a reasonable cost.
1.7
System extension
The mono-radar information "dubious XPDR" carried by the ASTERIX format is sent in the multi-radar
processing system of the control centre, where it can be correlated with the same data coming from the
other radar. This reinforces the validity of the message displayed to the controller.
One can also introduce the information " dubious XPDR" in the algorithm developed in the following notice
thereunder " Use of the Multiradar process for the detection of Out-of-norm XPDRs ". The final algorithm
would increase its efficiency.
1.8
Conclusion
This idea of using the local process of the monopulse interrogators in order to detect out-of-norm XPDRs is
submitted to the STFTV Group.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A13 - 3
2
U s e of the Multi-r a da r pr oc e s s for the de te c tion
2.1
Introduction
The aim of this document is to propose to the Group a first approach of functional specifications of a
" Failing transponders detection " function in the multi-radar process.
2.2
Definition of the airspace affected by the new function
Following the Radar Surveillance Norm, the SSR radar coverage in the ECAC member States must be
provide by a minimum 2 radar ( + one primary radar in the large TMAs ). At least, it is the short term
objective.
In fact, the real coverage is provided generally by more than 2 radars in a large part of the airspace .
It is possible to know with enough precision, for each point in space, the number of radars that are able to
detect an aircraft in this area.
We decided to exclude from in the Alert System function that we develop in this proposition, all the areas of
the airspace where the information would not be sure in regard to the radar coverage.
The airspace concerned is the one that is covered by at least 2 SSR radars .
It is evident that many areas will escape the surveillance provided by the new function. However, the
important volume of the covered airspace plays in favour of the adopted solution.
The algorithm needs to split the space in individual volumes, whose size and shape are defined by :
2.3
•
the number of radars allocated to each volume,
•
the simplicity of the computation ( see here under).
Basic principle
An aircraft enters the area covered by the multi-radar process of a control centre.
At any instant, the amount of radar " seeing" the aircraft is known in each of the individual volume.
The XPDR is detected as "failing" if
•
1] at least one radar does not see the aircraft,
•
2] the XPDR replies are not garbled,
•
3] this 1 & 2 situation does not continue more than N periods, where N is to be determined by
experimentation. This time delay avoids some unusual problems and takes into account the not
100 % detection probability of the radar, ...
When the " failure" is detected, one add to the multi-radar track format a flag, so as to be presented on the
controller's display. Being informed, he then informs the pilots
2.4
Details to solve
One radar may be failing, preventing or reducing the aircraft detection, in the presence of correct XPDR
replies.
Such a situation leading to wrong conclusions on the behaviour of the XPDRs, the system must be
immediately alerted to a radar problem.
The system must also determine, on-line, in which area ( see above) of the multi-radar airspace the aircraft
is located; the individual volumes must therefore be simple and reduced in number.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A13 - 4
Besides, these volumes have necessarily horizontal borders
Volume 3 : 4 radar coverage
Volume 2 : 3 radar coverage
Volume 1 : 2 radar coverage
Volume 1 : 0 or 1 radar coverage
Ground
If the position of the multi-radar track can be known with enough accuracy in the horizontal plane, the
vertical one is completely dependant on the Mode C. And this one can be incorrect precisely because the
XPDR is failing. The altitude must therefore be accepted with some care. A useful correlation could maybe
benefit from the flight plan information in this respect.
Besides, the Mode C information is a Flight Level, thus depending on the temperature and the QNH at that
moment in the atmosphere, while the volume geometry described above is determined in the absolute.
Therefore, positions will be defined in the relevant volumes with computed margins.
The algorithm described in 2.III needs the garbling information. This last one is transmitted by the SSR
radar. Nevertheless, the situation to which the garbling character is attached must be correctly standardised.
This standard is given by the ASTERIX format.
2.5
Conclusion
The proposed algorithm is submitted to the Group. It is very simple. Other more complex ideas may be
proposed like real time surveillance of A & C codes given by the different radars.
Nevertheless, it seems that a first step should consist of an analysis, off line, of the behaviour of this
algorithm. One could
•
use a flying aircraft, equipped with a voluntarily out - of - norm XPDR,
•
analyse the multi-radar process recordings which radars did see the aircraft and which did not.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A13 - 5
ANNEX
°14
Working Paper on an Initial RASS RTQMS
( Real Time Quality Monitoring System )
This working paper briefly describes a proposal for the initial version of a RASS Real-Time Quality Monitoring System
(RTQMS) which could easily be extended to comprise standardized Real Time Quality and Control (RTQC) features.
The proposed concept is based on a (pseudo) real-time link between a RASS-C station and a number of RASS-S
stations. A RASS-C station is assumed to be permanently installed at a Center whereas RASS-S stations are
assumed to be installed at relevant radars. One RASS-S station may provide services to more than one RASS-C
station. Possible inter-connections between RASS-C systems could be foreseen in the future as well.
A RASS-S station should be able to operate in two different modes of operation. In the local or stand-alone mode,
RASS-S will not interface with any of the RASS-C stations whereas in the remote mode , RASS-S will provide on
request and on a (pseudo) real-time basis, relevant information to any RASS-C station.
Such a (pseudo) real-time inter-connection provides the basic capabilities for the future realization of functionality to
test Surveillance System Inter-Operability aspects (e.g. Mode-S Cluster Management) and to perform Real Time
Quality Control (RTQC).
In the local mode, where the RASS-S station in question is not connected to any RASS-C station, it can be used to
perform local site-based radar quality and transponder quality assessment and other maintenance functions. For this
purpose, RASS-S will receive and/or inject signals at various stages of the radar chain (e.g. on Remote Field Monitor,
RF and Video Level). This technique provides, amongst others, the possibility to determine the aircraft reference
trajectory more accurately. By comparing this aircraft reference trajectory with the plot or local track output of the
radar under test, the relevant radar quality figures can be derived.
In addition to the previously introduced local mode of operation, RASS-S should also be able to work in the so-called
remote mode of operation. For the remote mode of operation only a limited subset of the complete RASS-S firmware
will be required.
In the remote mode, upon a RASS-C request, information such as accurate RASS-S reference trajectories and
quality figures for certain critical characteristics, such as antenna pattern deformation and RF/Video signal
degradation, can be provided by the RASS-S station in question. Also radar performance degradation and the results
of the Transponder Quality Assessment could be forwarded to the relevant RASS-C stations. Normally, this provision
of information should be performed in a kind of pseudo real-time snapshot type of operation. Also real-time provision
of this type of information over a limited coverage seems feasible.
In the remote mode of operation, the RASS-C IOSS Sub-System should be able to retrieve from the Center LAN the
RASS-S reference extraction information as well as the normal radar plot data of ASTERIX Categories 001, 002 and
016. By using the relevant RASS-S reference extractor output data as provided by all logically connected RASS-S
stations, RASS-C can thereafter chain and reconstitute a more accurate "Multi-RASS-S Reference Extraction
Output".
The format in which the RASS-S reference extractor output will be provided should closely resemble the existing
ASTERIX categories 001, 002 and 016. Additional flags, indication phenomena such as beam distortion or other type
of plot degradation will be added to facilitate subsequent RASS-C trajectory reconstitution.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A14 - 1
The setting up of a Point-to-Point connection between a RASS-C station and on individual RASS-S station should be
quite similar to the exchange of ARTAS ASTERIX Category 252 Session and Service Control messages. A graphical
representation of the RTQMS concept is presented below:
Sj :
S1
S3
S2
Coverage of
the RASS-Sj
tool through
its attached data
S4
RASS-Ci User Domain of interest for RASS-S3
Setting up a RASS-Sj service with RASS-C IATA Centre is similar to the exchange of ASTERIX
at 252-session Control Message :
• Identification of requesting RASS-Ci station
• Time interval of measurements
( start time, stop time )
• Time Interval of Result - Handover ( "
"
"
" )
• Type of Service such as, e.g. :
- request for Site Reference Trajectory
information similar to categories 001, 002 & 016 ( 25/50 meter σ )
- request of Transponder - related Quality Information
- report Degradation of Sensor Performance
Fig. 1 : Graphical representation of the proposed RTQMS concept.
For a given period of time (called a snapshot), a RASS-C station could request a RASS-S station to perform a
particular type of service and to provide the relevant results of this service in a defined time interval (minimize
network load). The service should be limited to the indicated RASS-C User Domain of Interest being defined in the
relevant Category 252 Session and Service Control messages. If the Domain of Interest would larger than the
coverage of the RASS-S station, error messages should be provided.
In the context of the RASS-C Input Output Sub-System (IOSS) developments, it is already foreseen to include a
RASS-C IOSS mode of operation whereby the RASS-C IOSS will set up a Point-to-Point connection to an ARTAS
Unit. This will be performed on the basis of exchanging
ASTERIX CAT 252 Session and Service Control
messages. An example, describing such an exchange of this type of information, is presented in Annex A.
With minor modifications to this software, it can be extended to set up a Client/Server link between RASS-C and
RASS-S.
A typical service requested from RASS-S, could be the request to provide an Air Situation Picture in a particular User
Domain of Interest. The required type of software for this purpose is very similar to the one currently being developed
as part of the RASS-C IOSS project.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A14 - 2
Of course, an ASTERIX category would have to be defined and created for this purpose. Its relevant fields would
have to be defined in all details (e.g. type of service, error messages, ....). The RASS-C IOSS should have the
possibility to record the original ASTERIX categories 001, 002 and 016 plot data as well as the equivalent RASS-S
reference extraction output which should closely resemble the categories 001, 002 and 016.
It is expected that the RASS-S positional reference extraction accuracy will be in the order of 25 to 50 meters.
Combining this information at Center level (e.g. 1 RASS-C station and 4 RASS-S Stations with common coverage)
could significantly improve this accuracy. The order of magnitude of the reconstruction errors will be small enough to
adequately support tracker quality assessment.
Access to the operational network could be done by using the existing RASS-C IOSS firmware and the existing
RASS-S firmware. The additional development costs compared to the currently planned RASS-C and RASS-S
development costs are minor. No additional firmware would be required on top of the RASS-S and RASS-C baseline
configurations.
With the same RASS-S firmware, all relevant parameters describing the Transponder Quality, could also be easily
measured. Parameters such as Transponder Power, Frequency Deviation and Pulse Degradation could, upon
request by RASS-C, be measured by RASS-S and forwarded to the Center whereafter proper reporting to Technical
Monitoring and Control and may be the Operational Services (e.g. supervisor) could be performed. If required,
labeling with Flight Plan information could be performed to assure unique aircraft identification.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A14 - 3
ANNEX
°15
Present BITE in airborne equipment
Author : Jérôme AMANRICH / STNA 4
Object : Report on the French transponder trials
This information is an abstract from an AEROSPATIALE document., the summary being done by the STFTV.
It is only intended to serve in the present STFTV report and should not be regarded as a technical or a reference
document.
A15.1 The BITE in its context
The BITE is part of a Central Maintenance Concept, that is based on the following items :
1
Equipment (aboard the a/c ) are conceived with more and more BITE devices.
2
A Central Maintenance unit ( computer & data base & displays ) collects, on a continuous basis, the status of
each BITE-equipped unit.
3
This information is both stored in the CMU and transmitted to the ground, either on-line, either during some
defined flight paths.
4
In parallel to this maintenance chain, the operational system may address an alarm to the pilot, for
information and possible action.
A15.2 Economic aspects of the Maintenance
The cost of the maintenance is about 18 % of the annual expenses of a revenue flying aircraft, and 60 % of the total
cost over the lifetime. So, everything is done to reduce its amount.
Important indicators are
♦
1 ) ratio
Mean Time Between Unscheduled Removal
Mean Time Between Failure
2 ) ratio
% of Operational Reliability
The ratio 1 lays around 0.50 , that is, one " problem " every two is a failure in the unit; 5 % correspond to
interconnections . The other half are untimely messages, caused sometimes by BITE erroneous data, but MOSTLY
by a (maintenance ) system message, justified but not affecting the incriminated unit.
Aircraft assemblers and installers try to improve this ratio to a 0.85 figure; presently, some devices are said to reach
0.70.
♦
The second ratio, 100 - # of interruptions , lays around 99 % (98.5 to 99.5 ) for recent a/c generation .
# of normal flights
An interruption is caused by any a/c or system malfunction or by a necessary verification or a corrective action, that
can occur both before departure, leading to delays larger than 15 min, or in the air, leading to either comebacks or
derouting to another airport.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A15 - 1
♦
One can increase the theoretical efficiency of the maintenance ( e.g. by adding more and more detectors,
BITE, ... ) but a more complex maintenance system introduces a higher probability of untimely error messages.
The resulting product of the two factors is shown thereunder, where it is possible to observe an optimum around a not
too complex system :
Maintenance Performance
reliability of the
solution
theoretical efficiency
global efficiency
Maintenance System complexity
A15.3 On Condition Units / LRUs
For each type of unit, called Line Replaceable Unit, the Equipment Installer makes his choice for both
- the equipment or units
- the type of fault detection that will be transmitted to the CMS.
But he has to present to the aircraft assembler an analysis of the fault probability, that will be part of the acceptance
of the global acceptance of the flying characteristics to be approved by the certification authorities, what is called the
On Condition units.
Two types of LRUs exist : 1 - Seller Furnished Equipment’s
2 - Buyer Furnished Equipment’s
the second is taken " of the shelf "; e.g. transponders, weather raiders, UHF radio, radio altimeters, ...
Although being normalised, some units may have to be chosen depending on other equipment, because of safety
reasons .
A15.4 Aircraft Maintenance Systems
♦
Various systems exist and their exact contents are neither normalised at ICAO level, neither completely
described for competition reasons between both aircraft and systems manufacturers.
But the ARINC group did issue some recommendations concerning the signals to tests, the test procedure,
etc... ( ARINC 624 ).In addition, for recent AIRBUS programs, design rules concerning the BITE are clearly
defined in the maintenance instructions. However, for reasons of industrial propriety, these instructions are
not published.
♦
The maintenance concerns
the structure
the motors
the systems.
To execute this maintenance, monitoring systems have been developed, that use sensors, a central
processor, and an events memory.
♦
Each element of the controlling system can itself be source of failures or false alarms, and the probability of
its occurrence increases with the increase of computers, of buses and of software lines exploding
geometrically from one generation to the next. The number of LRUs controlled is also increasing.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A15 - 2
♦
To reduce the cost of the maintenance, one follows these guidelines :
- one replaces the knowledge by skilled technicians of the internal functioning of each LRU by general
procedures of detection, executed by less skilled personal, of either faulty elements in the LRU or the
decision that the LRU is faulty and must be replaced; if necessary, the repair itself is done afterwards by the
manufacturer.
- the various displays and buttons that were used before, following complicated maintenance
documentation’s devoted to each individual equipment (and even different for each manufacturer) are
replaced by a common monitoring display, easy to manipulate and in simplified English. It follows a
successive approach principle where the faulty part is accessed deeper and deeper after each step of the
procedure, down to the component to replace if necessary. The reason of the failure is also obtained
through this procedure.
A15.5 Central Maintenance System
♦
The concept :
Aircraft system
Operational data
Maintenance data
Flight Warning
Computer
EIS indication
or
Local indicaton
Central Maintenance
Computer
MCDU
printer
data
loader
ACARS
pilot information
VHF
Log Book
CMS report
Company ( ground )
LRU fault paper
♦
Maintenance Modes :
- normal : continuous report, failure analysis >>
{ pilot informed
{ CMC
loaded
- interactive ( off-line ) : the operator uses the MCDU to dialogue with the CMC and
{ reads the loaded data *
{ applies tests
( * : other more detailed data about the failures can be sent via the ACARS route. )
( MCDU = Multipurpose Control & D isplay Unit)
A15.6 Maintenance Organisation
Each LRU is analysed
either in the unit itself and the result of the analysis only are transmitted to the CMC for synthesis, providing
they are coded in a well defined way,
or, the primary data of the LRU's BITE are sent to the CMC that does all the job.
The first form, the Distributed System, is preferable, because
it allows any autonomous way of BITE and analysis, making it more efficient, imagined by the
equipment's manufacturer ( and gives the possibility to continuously improve its products ),
it does not need to modify the CMC after each BITE modification
the tests done by the menus of the MCDU are driven by the BITE only and does not depend on the
CMC possibilities.
• STFTV •
[ Final Report to SURT ][ May 1995 ]
page A15 - 3
The second form imposes to each manufacturer of a defined type of equipment (e.g. a XPDR ), to send always the
same data, so that the analysis works on the same basis. It is a difficult and conservative way of processing.
A15.7 BITE coding
Two BITE information are used by old generation of transponders :
♦
The flight conditions existing at the occurrence of the detected failure. Their number is defined by the
manufacturer and are limited to a few values : e.g. the altitude code and the instant time at the occurrence of
the failure.
♦
Up to now, the failure code was limited to 32. With the next generation of aircraft, the number of failure
codes have been increased to a maximum of 255. The aim of the manufacturers is to reinforce the
possibilities regarding software debugging.
It is possible, directly from the MCDU in the cockpit to analyse the behaviour of LRUs.
It is of the highest interest to the Transponder Verification to remotely extract this information.
A15.8 Maintenance Types
♦
Schema :
Systematic
}
} at any airport
On Condition
}
Programmed visit at home base
Repair
♦
♦
level 1
in work hall
level 2
Components
level 3
the faulty LRU may
•
force immediate return ( if in the air ) or stop ( before take-off )
•
need replacement at next landing
•
need replacement at home-base only
•
wait till next scheduled maintenance.
the safety level depends on the importance of the LRU on a safe use of the aircraft, on the amount of
redundancy of that LRU :
e.g. suppose 3 identical LRUs exist and one unit is enough but essential for a safe flight and landing; when
a first unit fails, one may wait the next landing for replacement ( the safety level being reduced one step), but
if a second unit fails during the same flight, the aircraft must land immediately because the next failure would
put the aircraft in danger...
A15.9 Maintenance Data Transmission to the user ( the company)
Presently, these data are transmitted by the ACARS network, where it exists, using VHF aircraft to ground support.
The Company that operates that aircraft may decide either
•
to request the results of the CMS to be sent in real time
•
to receive them during one specified flight path ( e.g. during approach )
•
to receive them on pilot action ( e.g. when fault alarm appears to him.
Some companies even ask for a world-wide on-line transmission ( via the SITA network ) of the maintenance data to
the home base of their fleet, for in-time stock supply and maintenance logistic.
A15.10
Conclusion
The actual evolution by aircraft and equipment manufacturers is to reinforce the capability and the accessibility of
BITE information. The equipment manufacturers will have to develop and increase the BITE functions under pressure
from the aircraft manufacturers and, indirectly, from companies.
In this view we have to find different opportunities using this system in transponder surveillance and verification.
#
• STFTV •
#
#
[ Final Report to SURT ][ May 1995 ]
page A15 - 4