|Date:||Sunday 10 January 1954|
de Havilland DH-106 Comet 1
|Operator:||British Overseas Airways Corporation – BOAC|
|First flight:||1951-01-09 (3 years )|
|Total airframe hrs:||3681|
|Engines:||4 de Havilland Ghost 50|
|Crew:||Fatalities: 6 / Occupants: 6|
|Passengers:||Fatalities: 29 / Occupants: 29|
|Total:||Fatalities: 35 / Occupants: 35|
|Aircraft fate:||Written off (damaged beyond repair)|
|Location:||16 km (10 mls) S off Elba ( Italy)|
|Phase:||En route (ENR)|
|Nature:||International Scheduled Passenger|
|Departure airport:||Roma-Ciampino Airport (CIA/LIRA), Italy|
|Destination airport:||London Airport (LHR/EGLL), United Kingdom|
Comet G-ALYP left Rome-Ciampino Airport (CIA) at 10:31 on a flight to London. After taking off the aircraft was in touch with Ciampino control tower by radio telephone and from time to time reported its position. These reports indicated that the flight was proceeding according to the B.O.A.C. flight plan and the last of them, which was received at 10:50, said that the aircraft was over the Orbetello Beacon. The captain of another B.O.A.C. aircraft, Argonaut G-ALHJ, gave evidence of communications which passed between him and G-ALYP. The last such message received by the Argonaut began ” George How Jig from George Yoke Peter did you get my ” and then broke off. At that time, approximately 10:51, the aircraft was probably approaching a height of 27,000 feet. The Comet descended and crashed into the sea off the Island of Elba.
Initial examination and reconstruction of the wreckage of G-ALYP revealed several signs of inflight break-up. Shreds of cabin carpet were found trapped in the remains of the Comet’s tail section; The imprint of a coin was found on a fuselage panel from the rear of the aircraft; and Smears and scoring on the rear fuselage were tested and found to be consistent to the paint applied to the passenger seats of the Comet.
When most of the wreckage was recovered, investigators found that fractures started on the roof, a window then smashed into the back elevators, the back fuselage then tore away, the outer wing structure fell, then the outer wing tips and finally the cockpit broke away and fuel from the wings set the debris on fire.
To find out what caused the first failure, BOAC donated G-ALYU for testing. The airframe was put in a huge water tank, the tank was filled, and water was pumped into the plane to simulate flight conditions. After the equivalent of only 3,000 flights investigators at the Royal Aircraft Establishment (RAE) were able to conclude that the crash had been due to failure of the pressure cabin at the forward ADF window in the roof. This ‘window’ was in fact one of two apertures for the aerials of an electronic navigation system in which opaque fibreglass panels took the place of the window ‘glass.’ The failure was a result of metal fatigue caused by the repeated pressurization and de-pressurization of the aircraft cabin. Another worrying fact was that the supports around the windows were only riveted not glued, as the original specifications for the aircraft had called for. The problem was exacerbated by the punch rivet construction technique employed. Unlike drill riveting, the imperfect nature of the hole created by punch riveting may cause the start of fatigue cracks around the rivet.
The Comet’s pressure cabin had been designed to a safety factor comfortably in excess of that required by British Civil Airworthiness Requirements (2.5x P as opposed to the requirement of 1.33x P and an ultimate load of 2x P, P being the cabin ‘Proof’ pressure) and the accident caused a revision in the estimates of the safe loading strength requirements of airliner pressure cabins.
PROBABLE CAUSE: “We have formed the opinion that the accident at Elba was caused by structural failure of the pressure cabin, brought about by fatigue. We reach this opinion for the following reasons: –
(i) The low fatigue resistance of the cabin has been demonstrated by the test described in Part 3, and the test result is interpretable as meaning that there was, at the age of the Elba aeroplanes a definite risk of fatigue failure occurring.
(ii) The cabin was the first part of the aeroplane to fail in the Elba accident.
(iii) The wreckage indicates that the failure in the cabin was of the same basic type as that produced in the fatigue test.
(iv) This explanation seems to us to be consistent with all the circumstantial evidence.
(v) The only other defects found in the aeroplane were not concerned at Elba, as demonstrated by the wreckage. “