Airbone New and Advanced Satellite techniques and Technologies in A
System Integrated Approach
Eurocae WG28 SG4
Wolfgang Schuster, DPhil
Research Fellow (Imperial College London)
27-29 March 2006
Toulouse
ANASTASIA Consortium
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27 March 2006, Toulouse
Contents
ILS Overview (1)
ILS Performance (8)
Performance Issues (2)
ILS vs. GBAS errors (4)
Conclusions (1)
ILS Overview
LOCALIZER (Top View)
DM of 150 Hz AM
predominates
DM of 90 Hz AM
predominates
DM of 90 Hz AM
predominates
GLIDESLOPE (Lateral View)
DM of 150 Hz AM
predominates
~ 3o
Flaring Height?
use of radio-altimeter
Carrier amplitude-modulated by 2 tones
Depth of Modulation (DM) = function of angle
Receiver measures DM of each tone, computes difference (DDM)
ANGULAR position
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ILS Performance (1/8)
Error = change in DDM at a given angle with respect to the
nominal (expected) DDM at that angle (either due to transmitter
or receiver).
ILS performance specifications from
ICAO-Annex 10 (Vol 1)
ICAO-8071
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ILS Performance (2/8)
LOCALIZER Source of Error
Error Magnitude
Applicability Limits
Course Alignment – 3.1.3.6.1.c
3 m (rare occasion)
At ILS Ref. Dat.
Bends on MEAN course line – 3.1.3.4.2, Att. C-2.1.4: at 95%, Fig C-1
0.031 DDM
0.031 – 0.005 DDM
0.005 DDM
0.005 – 0.010 DDM
Out – A
A–B
B – ILS Ref. Dat. – D
D–E
Vertical polarization at 20 degrees bank – 3.1.3.2.2.2 (relevant for
Cat-II?)
0.005 DDM (=5muA)
0.02 DDM
RF Interference at 0.1 – 10 Hz: Course Line fluctuations – 3.1.3.2.3
0.005 DDM p/p
N/A
Displacement Sensitivity – 3.1.3.7.2 (Localizer)
10%
N/A
DM due to carrier at power supply freq. or harmonics (ripple) –
3.1.3.5.3.2 and due to harmonics, unwanted noise – 3.1.3.5.3.2
0.5% + 0.05%
N/A
Receiver Centring Tolerance – Att.C-2.2.3.1
1.66% 0.00258
DDM (at 68%)
Full-width
Receiver displacement sensitivity tolerance – Att.C-2.2.4.1
0.019 DDM (for
15.35% - 24.65%
0.008 DDM (18-22%)
(Table I-4-7 of 8071)
20%
Until 0.155 DDM
DM due to Carrier DDM fluctuations – 3.1.3.5.2 (I-4-7)
Displacement linearity Receiver (difference between input and
output) – Att.C-2.2.6.1
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ILS Performance (3/8)
GLIDE SLOPE Source of Error
Error Magnitude Applicability Limits
Glide Path Adjustement – 3.1.5.1.2.2
0.04 theta
N/A
Glide Path Bends on mean glide path (95%) – 3.1.5.4.2
Att. C-2.1.5: 1.2 m (95%) at ILS R.D.
0.035 DDM
0.035 – 0.023 DDM
0.023 DDM
Out – A
A–B
B – ILS Ref. Dat.
RF Interference at 0.01 – 10 Hz: GS fluctuations – 3.1.5.2.3
0.02 DDM p/p
N/A
Angular displacement sensitivity – 3.1.5.6.8
15%
N/A
DM due to carrier at power supply freq. or harmonics (ripple)
– 3.1.5.5.2.2
1%
N/A
Receiver centring tolerance – Att.C-2.2.11
3.33% (0.0058 DDM)
at 68%
Full-width
Receiver course displacement sensitivity – Att.C-2.2.12
0.016 DDM for
34.75% - 45.25%
0.0076 DDM for
37.5% to 42.5%
N/A
20%
N/A
DM due to Carrier DDM fluctuations – 3.1.5.5.1.
Receiver displacement linearity (between input and output) –
Att.C-2.2.14
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ILS Performance (4/8)
Localizer – Monitoring Alerts
Error Monitored
Location
Limit before Alert
Time before Alert
Shift in mean course line –
3.1.3.11.2.c
ILS Ref. Dat.
6m
2 seconds (1 s?)
Variation in Displacement
Sensitivity – 3.1.3.11.2.f
N/A
17% from nominal
2 seconds (1 s?)
Glide Slope – Monitoring Alerts
Error Monitored
Location
Limit before Alert
Time before Alert
Shift in mean glide path –
3.1.5.7.1.a
N/A
–0.075 theta to
+0.10 theta
2 seconds (1 s?)
Variation in Displacement
Sensitivity – 3.1.5.7.1.e
N/A
25% from nominal
2 seconds (1 s?)
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ILS Performance (5/8)
Geometrical Considerations
3000 m
572.4 m
D
LOC
Pt. C
ILS R.D. at 30 m
TH
900 m
100 m
at 15 m
286.2 m
GS
Transmitter
Slope = 3 degrees
Error Interpretation
Not entirely clear…
ICAO-8071 – 4.1.5: “…measurement uncertainties… two-sigma or 95%...”
ICAO-8071 – 4.2.55: “…whether 99.7% (i.e. three-sigma) … are within limits…”
Path bends at 95%.
Receiver centring tolerance at 68%...
Investigate both assumptions: a) 95% and b) 99.7%.
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ILS Performance (6/8)
Monitor Limits
Assumed to be at the FIVE sigma level.
Error Calculation Assumptions:
Same as in Draft v0.5
MIN(adjust-maintain, monitor) Justification?
Linearization Point:
Laterally at Pt. D: most stringent scenario (corresponds to end of
touchdown box)
Vertically: Threshold (i.e. at 50 ft) or higher (e.g. 100ft)?
• Flaring: 50ft to 30 ft ‘end-point’ in using glide-slope?
• Height at which radio-altimeter sets in for flaring?
• From discussion yesterday – 75ft
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ILS Performance (7/8)
Results
Localizer
Glide Slope
(+)Limits
Point of
Linearization
Adjust and
Monitor Limits
Error at 95%
D
95.2%
4.21 m
D
99.7%
3.89 m (cf. 3.58 m
from v0.5)
TH (50 ft)
95.2%
0.76 m - 1.34 m(+)
TH (50 ft)
99.7%
0.70 m - 1.31 m(+)
C (100ft)
95.2%
1.52 m - 2.68 m(+)
C (100ft)
99.7%
1.39 m - 2.61 m(+) (cf.
1.36 m from v0.5)
for bends from Att.C-2.1.5 instead of Sect. 3.1.5.4.2 of ICAO Annex 10 (Vol 1)
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ILS Performance (8/8)
Results (cont’d)
Additional error sources of ILS:
~ +8.7% (laterally)
~ +2.2% (vertically)
Errors quoted at 2 sigma instead of 3 sigma:
~ +8.2% (laterally)
~ +9.4% (vertically)
Errors on Glide Path Bends from Att.C-2.1.5 instead of Sect. 3.1.5.4.2:
~ +76.3%! (vertically)
Significant range of values
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Contents
ILS Overview (1)
ILS Performance (8)
Performance Issues (2)
ILS vs. GBAS errors (4)
Conclusions (1)
Performance Issues (1/2)
ACTUAL performance of ILS?
Experimental data?
REQUIRED performance for Cat-II/III?
Safety perspective?
Autoland Method?
Other Method?
Some Issues…
Autoland horizontal touchdown position
Vertical touchdown speed?
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Performance Issues (2/2)
Estimated Position
Start of Flaring
Manoeuvre
True Position
Touchdown attitude (nose gear!)?
Radio-altimeter (very accurate height) at 75ft…
Slowly phase in at larger height? 100ft?
Radio + 2-D GBAS?
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Contents
ILS Overview (1)
ILS Performance (8)
Performance Issues (2)
ILS vs. GBAS errors (4)
Conclusions (1)
ILS vs. GBAS Errors (1/4)
Localizer (top view)
Glideslope (lateral view)
g
a
a
l
Along Glide Slope
P( Loc, GS ) = P( Loc) × P(GS )
95%
95%
2σl
2σg
P=
1
2πσ lσ g
−l 2
2σ l
e
∫ dl ∫ e
2
−g2
2σ g2
dg
Two independent 1-dimensional systems
Uncorrelated errors at NSE level
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ILS vs. GBAS Errors (2/4)
Horizontal Errors
(top view)
Vertical Errors
(lateral view)
a
σz
Direction of Travel
l
σx
σg
σy
ANASTASIA Consortium
ONE 3-dimensional system
x, y and z components not uncorrelated at NSE
level ([x,y,z] here could be any reference frame, not
necessarily WGS84)
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ILS vs. GBAS Errors (3/4)
y
Reference frames – 2D vs. 3D
g
l
GBAS σX σY and σZ
ILS
x
σl and σg
 x  cos φ cos θ
  
 y  =  sin φ cos θ
 z   sin θ
  
th
e Pa
d
i
l
G
− sin φ cos α − cos φ sin θ sin α
cos φ cos α + sin φ sin θ sin α
− cos θ sin α
a
cos φ sin θ cos α − sin φ sin α  a 
 

− sin φ sin θ cos α + cos φ sin α  l 
 g 
cos θ cos α
ALONG-TRACK error?
Use DME error?
z
g
Actual position (unknown)
σv ≠ σg (GBAS v = local vertical)
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y’
x’
σg
Incidentally…
z
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Path
Glide
σx’
Computed
position
a
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ILS vs. GBAS Errors (4/4)
Two uncorrelated 1D vs. one correlated 3D
σ
σ xy σ xz σ xt 


2
σ
σ
σ
σ
y
yz
yt 
COV [ x] =  xy
σ xz σ yz σ z2 σ zt 

2
σ
σ
σ
σ
yt
zt
t 
 xt

2
x

cos 2 Ei cos 2 Ai
 ∑
σ i2
 i 2
 cos Ei cos Ai sin Ai
∑
σ i2
= i
 cos Ei cos Ai sin Ei
∑
σ i2
i

cos Ei cos Ai
 ∑
σ i2

i
∑
cos 2 Ei cos Ai sin Ai
σ i2
i
∑
cos 2 Ei sin 2 Ai
i
∑
σ
2
i
∑
cos Ei cos Ai sin Ei
σ i2
i
∑
cos Ei sin Ai sin Ei
cos Ei sin Ai sin Ei
σ
i
∑
i
2
i
cos Ei sin Ai
σ
σ i2
i
2
i
∑
sin 2 Ei
i
∑
i
σ i2
sin Ei
σ i2
cos Ei cos Ai 
∑i

σ i2

cos Ei sin Ai 
∑i

σ i2

sin Ei
∑i σ 2 
i

1
∑i σ 2 
i

−1
where Ei, Ai and σi are respectively the elevation, the azimuth and the pseudorange error residual
between user position and satellite i.
Errors between measurement variables x, y and z are correlated
Impact upon probability calculations? ILS yields errors at 95%...
Incidentally…
Lateral error has impact upon vertical error with respect to glidepath.
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Conclusions
Proposed Work
1.
Establish ACTUAL ILS performance
Experimental data?
2.
Establish REQUIRED performance for safe Cat-III landing
ILS Look-Alike vs. Autoland method – detailed analysis
New method?
3.
Translation of Cat-II/III RNP into ‘GBAS-errors’
Along-Track error?
Error correlation?
4.
Validate error model
5.
Derive Alert Limits for Category-II/III
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