FLIGHT International, 24 September (977
After looking at your home and
road fatality figures I concluded that
staying at home is dangerous (some
0 • 02 fatal accidents per million hours),
using the road is ten times more
dangerous, and GA pleasure flying is
some 2,000 times more dangerous than
being in the home. Even when using
the "professionally operated company
aircraft" the risks are high: 25 times
more dangerous than using the road.
You hoped that as a result of the
Cranfield Show the GA safety record
would approach that of the professional. The aim should surely be
greater safety for everybody, aspiring
perhaps to better the road-safety rate.
It is only when one looks at the
scheduled carriers' record that one
can boast of the comparison with road
travel. For scheduled commercial
carriers (excluding the USSR) the
fatal accident rate is about 1-5 per
million hours. Taking account of block
speed, it then becomes some 30 per
cent safer to fly scheduled carrier than
to use the road. You said: "Statistics
can be played any old way . . .". Please
try to play fair.
132 Peregrine Road,
Sunbury-on-Thames,
MoD's invincible safety indifference
SIR—I have followed the arguments
about the non-publication of military
low-level routes within the UK. It is
hard to understand t h e reluctance of
the Rritish authorities in this matter.
Here in Australia all military lowlevel routes are published in a booklet as part of the Aeronautical Information
Publications.
These
are
amended every few months.
A. L. PALMER
Middx
Let's hear it for North Sea A T C
SIR—The Sensor item for September
3 about RAH and Rristow crew dissatisfaction with CAA air traffic control over the North Sea comes as a
surprise to me. I have been operating
in the North Sea for almost five years,
over four of which were from Sumburgh. During that time offshore
traffic has increased tremendously,
imposing ever greater responsibilities
on the CAA and National Air Traffic
Services. In general they have coped
as well as can be expected of bodies
operating under severe financial constraints. At times there have been
delays in improving services, but the
operators have coped without any
reduction in flight safety.
For control of traffic outside the
Sumburgh ATC area the two main
helicopter operators operate an HF
area advisory control net that has
performed well in the absence of a
NATS-provided VHF net. NATS is
now establishing such a net, though
there will be shortcomings until
enough money is released for t h e provision of the repeater stations necessary for full coverage. In the meantime, the operators are providing a
back-up service to fill in the holes.
Within the Sumburgh and Aberdeen
ATC areas the former copes partial-*
larly well with a large amount of
traffic in a physically and meteorologically restricted area. Traffic is
handled efficiently in spite of peak
periods which severely test controllers
and ground facilities, and I can't
remember any instance of a controller
jeopardising safety or being less than
courteous, helpful and cheerful.
Croft House,
T. L. WOLFE-MILNER
Maryculter,
Aberdeen AB1 0BW
Each chart (see example above) contains full information for each sector.
When these routes are activated by
Notam civil pilots are given information on military movements. This
system works very well in Australia,
especially in areas of dense generalaviation traffic.
Astral Airways,
KEVIN SWIGGS
East Devonport,
Tasmania
HEAO: not the Alpha of X-rays
SIR—Flight's September 3 report of
the successful launching of the HEAO
X-ray s a t e l l i t e
says that US
astronomers now have ". . the first
opportunity to observe from space the
X-rays emitted by pulsars, black holes
and quasars."
Do we Rritish never do anything?
Well, as a matter of fact we do. On
December 6, 1973, you reported this
laboratory's X-ray observations of
Cygnus X-l, ". . . long suspected of
being a black hole." We were using
our X-ray telescope, the first of its
kind to go into orbit, in Nasa's
Copernicus spacecraft, which celebrated its fifth birthday on August 21.
Spacecraft and instruments are still
doing well.
Ariel V, coming in to its third
birthday on October 15 and also doing
well, has harvested a wealth of information on a growing menagerie of
exotic objects. It is a firitish satellite
carrying five Rritish X-ray instruments, of which two are from this
laboratory.
I wish HEAO well. Hut though
Copernicus, Ariel V and HEAO have
905
(or will have) uniquely important
observations to their credit, none
claims to be the first X-ray space
observatory. That honour goes to the
US Uhuru satellite
Mullard Space
PROF R. L. F . BOYD
Science Laboratory,
Holmbury St Mary,
Dorking, Surrey
Relics of a lost planet
SIR—The photos of Phobos (Flight,
July 30) showing features which lead
some scientists to speculate that it is
about to break up raises the whole
question of Roche's Limit. When my
own astronomical studies reached
their peak more than forty years ago
the textbooks of the day simply
asserted that if a satellite approaches
within 2-45 radii of its primary it
would be broken apart by the
"tremendous tidal forces" exerted by
the planet.
Since Newton's universal theory of
gravitation is a simple inverse square
law, it follows that gravitational forces
near the surface of the Earth must
be greater than those 2-45 Earth
radii distant. Consequently, I always
wondered why aircraft could cruise
a few thousand feet high without any
signs of being broken up. Moreover,
artificial Earth satellites are showing
an equal ability to ortfit safely well
within the confines of Roche's Limit.
On all their journeys to the moon and
back the Apollo spacecraft twice
traversed this zone without giving the
slightest sign that they were about
to be broken up.
All this leads me to believe that
Roche's Limit is invalid or applicable
only to bodies above a certain critical
size and mass. Since the largest of the
asteroids—themselves believed to be
the remnants of a former planet which
passed too close to Jupiter—are only
a few hundred miles in diameter, I
would put these limits at a diameter
above a thousand miles and a mass
more than one-tenth that of the Moon.
It may be significant that recently
deduced rings of Uranus are believed
to consist of lumps of material as big
as the largest asteroids
The observational evidence (as distinct from pure theory) thus suggests
that both of the Martian satellites are
much too tiny ever to be torn asunder
by "tidal forces". Mars will therefore
never acquire a ring system. Since the
furrows responsible for this speculation resemble lunar features, it seems
probable that they all had a common
origin.
If the furrows really are fracture
phenomena, a far more fascinating
possibility arises. The satellites of
Mars are believed to be captured
asteroids. As mentioned above, the
asteroids are thought to be remnants of a planet which once lay
between Mars and Jupiter. If this is
correct, a proportion of the asteroids
would be pieces of matter which once
formed part of the actual surface of
the parent body. It is theoretically