Comet 1

Image: Ian Dunster • Licensed for reuse under CC BY-SA 3.0

On Sunday 10 January 1954, BOAC Flight 781, a De Havilland DH.106 Comet 1, registered G-ALYP, took off from Ciampino Airport in Rome, Italy, en route to Heathrow Airport in London, England, on the final leg of its flight from Singapore. At about 10:51 GMT, the aircraft suffered an explosive decompression at altitude and crashed into the Mediterranean Sea, killing everyone on board. The accident aircraft was the third Comet built.

There were 6 crew and of the 29 passengers, 10 were children. Among the casualties were Chester Wilmot, a prominent Australian journalist and military historian working for the BBC, and Dorothy Beecher Baker, a Hand of the Cause of God for the Baha'i Faith.

At first the task of finding out what happened was difficult. In 1954, there were no black boxes, no Cockpit Voice Recorders or Flight Data Recorders, so assessment was difficult. Established protocol for aircraft accident investigation did not exist.

An extensive search for the aircraft was organised including the Royal Navy ships as well as a civilian salvage vessel from Malta. The search involved the pioneering use of underwater TV cameras, developed by a team at the UK Admiralty Research Laboratory, to help to locate and salvage the wreckage in deep water.

Witnesses to the crash were a group of Italian fishermen who rushed to the scene to recover the bodies and to find possible survivors, of which there were none. To find more evidence concerning the cause of the crash, the bodies were brought to the coroner for autopsy. During the examination, pathologist Antonio Fornari found broken limbs and damaged limbs, which occurred after death. But Fornari also discovered a distinct pattern of injuries, which were identified as the cause of death, in most of the victims. These injuries consisted of fractured skulls and ruptured and otherwise damaged lungs. Fornari found no evidence of an explosion, and he felt confused by the pattern of injuries.

The ruptured lungs were a sure indicator that the air cabin depressurised because the sudden decrease in pressure. To support the theory and also to confirm the cause of the skull fractures, the crash was simulated at the Royal Aircraft Establishment (RAE) in Farnborough using the same conditions of the actual plane prior to crash. To do this experiment, a model fuselage was constructed similar to that of the Comet.

Dummies were also seated within the fuselage to simulate possible movements of passengers during the crash. To simulate the crash, the investigators deliberately ruptured the model by increasing the air pressure within it until it exploded. The movement of the dummies within the air cabin at the moment of explosion showed the cause of skull fracture as they were thrown out of their seats and slammed head-first into the ceiling.

The World's first production Commercial Jetliner

BOAC Flight 781

Photo: Unknown • Believed to be in the Public Domain (No known Copyright restrictions)

Photo: Ministry of Transport • Believed to be in the Public Domain (No known Copyright restrictions)

Wreckage of the aircraft was eventually found on the sea floor and subsequently raised and transported to the Royal Aircraft Establishment for investigation. Upon examination of the wreckage it became obvious that the aircraft had broken up in mid-air, and initially it was thought that the aircraft might have been brought down by a bomb. Suspicion then shifted to the possibility of an engine turbine explosion, and modifications were put in hand to encase the turbine ring in other Comets with armour plate to contain a possible disintegrating turbine disk.

In the meantime, all Comets were to be grounded until these modifications had been carried out. The possibility of failure of the pressure cabin had been considered but then discounted due to the Comet's cabin having been designed to a considerably higher strength than was considered necessary at the time.

With most of the wreckage recovered, investigators found that fractures started in the roof of the cabin, a window then smashed into the elevators, the rear 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 large water tank, the tank was filled, and water was pumped into the plane to simulate flight conditions. The experiment was run 24 hours per day, 7 days per week.

lAfter the equivalent of 3,000 flights simulated with G-ALYU, investigators at the RAE were able to conclude that the crash of G-ALYP had been due to failure of the pressure cabin at the forward ADF window in the roof. This window was 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 pressurisation and de-pressurisation of the aircraft cabin. Another fact was that the supports around the windows were 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 caused manufacturing defect cracks, which may have caused fatigue cracks to start around the rivet.

Aeronautical engineering firms were quick to respond to the Comet's commercial advantages and technical flaws alike; other aircraft manufacturers learned from, and profited by, the hard-earned lessons embodied by de Havilland's Comet.

Source: Wikipedia

Images: Ministry of Transport and Civil Aviation • Believed to be in the Public Domain

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