Two official reports on the 31 October, 1999 accident involving an EgyptAir Boeing 767-300 around 100km (54nm) south of Nantucket off the US coast have revealed a radical disagreement in the interpretation of evidence.

The US National Transportation Safety Board (NTSB) - to which Egypt ceded control of the accident investigation although the crash occurred in international waters - states that the aircraft's dive to impact took place as a result of "the relief first officer's flight control inputs". It adds that the reason for his actions was not determined.

But a 200-page analysis by the Egyptian investigation team says: "A dual [elevator] power control actuator [PCA] failure is consistent with the known and predicted behaviour of the aircraft, and of all the recorded data concerning the accident. Although a dual PCA failure cannot be confirmed, however, it must be considered as a plausible cause of the accident." The aircraft crashed 31min after its 01:20 take-off from New York Kennedy bound for Cairo, Egypt, killing all 217 people on board.

The aircraft's flight profile, according to the NTSB, consisted of a normal climb to 33,000ft (10,000m), with the captain and co-pilot at the controls. Shortly after top of climb, the relief first officer persuaded the co-pilot to take his break early, which is non-standard - but the co-pilot agreed to the suggestion.

The captain left the flight deck to go to the lavatory, and while the relief first officer was alone at the controls, the aircraft nosed over at near 0g into a dive. The captain returned and asked several times: "What's happening?" to which the first officer did not reply.

With the captain also at the controls, the elevators turned up briefly, but then the left and right elevators split - the left up and the right down. This enables an elevator jam on one side to be overcome.

The NTSB's argument rests on two main points: the behaviour and speech of the relief first officer; and that it found no evidence of a pre-impact aircraft fault. As the dive began, the relief first officer, speaking "quietly", said 11 times in Arabic: "I rely on God," according to the NTSB.

The Egyptian team, however, says Boeing and the NTSB were selective in their testing, and notes that the right outboard elevator PCA has pre-impact damage "consistent with a jammed servo valve".

Source: Flight International