THE COMET RIDDLE
___________
Explanation of Jet Liner Crashes Poses New Questions About Metal Fatigue
By DREW MIDDLETON
LONDON - A mystery story in which the villain is a
mathematical ratio and
the detectives a group of somber, humdrum scientists reached its
concluding chapter in
London last week at a Court of Inquiry on the jet Comet. If the
story has a
heroine, it is the Comet, the sleek, swift symbol of Britain’s
challenge for
leadership in air transport which until this past spring, was the only
jet air liner in
operation on the airways of the world.
In January and again in April Comets crashed and the planes were
withdrawn from
service by the British Overseas Airways Corporation. The long patient
investigation
involving the Royal Navy, the Ministry of Supply and, most important,
the Royal Aircraft
Establishment at Farnborough began.
The findings of the R.A.E.’s investigation are the basis for the
Court of
Inquiry which sat in somber Church House. It is on this wad of research
four and one-half
inches thick and the conclusions to be drawn from it that much of the
future of British
civil aviation rests.
The two Comets that crashed were Mark 1’s. De Havilland, the
makers, have
already produced bigger and better versions in the Mark 11 and Mark
111. The latter is
intended for trans-Atlantic flights. It is hoped that they will restore
some of the
prestige lost by British aviation through Comet crashes.
Wreckage Recovered
The investigation by the R.A.E. which produced the
findings before the
court was the most detailed and exhaustive in the history of
aviation. Ships of the
Royal Navy, scouring the sea bottom off Elba, brought back 70 per cent
of the wreckage
of the Comet that crashed near that Mediterranean island last
January. The wreckage
- ball bearings, tiny scraps of metal, grotesquely twisted seats from
the cabin - was
fitted onto the wooden “ghost” of a Comet at Farnborough.
This mosaic was then immersed in thousands of gallons of
water. More water was
pumped into its fuselage to simulate the pressure the plane would
encounter at all stages
of a flight. Other devices imitated the buffeting of the winds. This
was the most
spectacular aspect of the investigation. But there was much more.
Day after day groups of scientists flew in Comets filled with
electric devices for
measuring stress and pressure. They took their lives in their
hands. For no-one knew
what had caused the crashes. There were, in fact, more that sixty
hypotheses before the
R.A.E. when the investigation began.
But all through spring and summer the planes took off into the
upper air over
England, flying so high that the North Sea lay bleak and bare to
the east and the
uneasy Atlantic rolled to the west. Like good detectives, the
scientists eliminated
suspects.
It wasn’t the crew; the crew were stricken in the execution of
their duty. It
wasn’t the design; there was some design faults but these were not
responsible. It
wasn’t the engines; the engines caught fire but only after “it”
happened.
It wasn’t sabotage.
Theories Discarded
One by one the theories were discarded until Sir
Arnold Hall,
director of R.A.E., concluded that there was only one remaining theory
to fit the facts
which reconstruction of the Comet had presented. These facts were that
the Comet G-ALYP
had suddenly burst open, hurling her passengers and crew to their
deaths and then, torn
and broken, had fallen through the clear Mediterranean air into the sea
below.
That was the way Comet “Yoke Peter” (the restored “ghost”) died
and because she died that way the “backroom boys” at Farnborough think
they know
what killed her. The murderer was metal fatigue. Broadly
speaking, metal fatigue
means that a structure which has an ample reserve of strength when it
is new, might fail
under its normal working load after a certain length of time.
But the killer is difficult to find. The precise scientific basis
of fatigue has not
yet been agreed upon. However, the R.A.E. believes that metal
fatigue is responsible
for the death of the Comet YP and probably for the crash of the
second Comet off
Naples in April.
In any complex structure there are points where there is a
local concentration
of stress. If the metal cannot withstand this stress the fracture
will occur no
matter how strong the rest of the structure.
What Happened
This apparently is what happened to the Comet. The
stress was about 70 per
cent of the ultimate near the corners of windows in the pressurised
cabin. The R.A.E. is
satisfied that the stress in the cabin became too great near one window
and the fracture
occurred.
It is still too early to say what can be done to meet the
challenge raised by
these two accidents. Much of the work done on metal fatigue
for aircraft up to
the present has been done on movable parts. But with pressurised cabins
necessary on
high altitude aircraft, the question now arises of metal fatigue
in relation to the
structure of the cabins.
The question is connected with the aircrafts’ service. Yoke Peter
had flown
successfully more than a million miles, Yoke Yoke, the second plane to
crash, had clocked
2,704 hours in the air. What is the connection between hours in the
air, or mileage, and
metal fatigue? Is there such a connection? Here, just as in some
mysteries where, although
the investigating authorities know the cause of the murder, they are
stumped about why,
the question remains why?
Fact Follows Fiction
Perhaps the oddest part of the inquiry into the two
accidents which cost
fifty-six lives is the manner in which the facts mirror fiction. Long
before the Comets
were in service a writer, Nevil Shute, wrote in “No
Highway” about a
trans-Atlantic plane which falls victim to metal fatigue.
The de Havilland company, which pioneered the development
of jet aircraft for
civil aviation, has already carried out a large number of modifications
on the Comet Mark
11 and Mark 111. But the question of metal fatigue is one which cannot
be met by
modification of these or any other aircraft, as they are now built. It
deals with the
composition of the “flesh and bone” of the aircraft, rather than the
design.
The investigation has been a race against time, with the de
Havilland engineers and
Britain’s aviation industry fighting to restore Comets to the
commercial
airways before jet transports could become available from other
manufacturers,
particularly those in the United States. No one knows yet whether that
race has been won.
Boeing’s long-range jet transport, already test flown at Seattle,
Wash., is
expected to be ready for commercial use by 1958. Although some
American-flag airlines have
ordered the new and larger Comets, the delay caused by the crash
investigation may make it
impossible for deliveries before Boeing’s deliveries.
In the meantime, B.O.A.C. has ordered several of the new
American-built
DC-7’s to bolster its fleet of fast, long-range airliners.
From: THE NEW YORK TIMES 24th October 1954
