David Learmount/LONDON
THE PRIMARY CAUSE of the Tarom Airbus A310-300 crash at Bucharest appears to have been a throttle lever which became mechanically jammed at the full-power position while the autothrottle was engaged, according to the official interim report.
All 49 passengers and 11 crew died when the aircraft came down in a snowstorm shortly after take-off on 31 March.
Slow reaction by the pilots in rectifying the resulting asymmetric thrust is apparent from the report of the Romanian Accident Investigation Committee (AIC), however. The asymmetry developed slowly over more than 40s, with the pilots taking no action until just before impact.
The report says that the co-pilot was flying the take-off from Bucharest manually, but with the autothrottle system (ATS) engaged and selected to take-off mode. It describes the aircraft climbing through 2,000ft (600m) at 190kt (350km/h), with the crew retracting flap according to the normal procedures "...at about the time the event began".
At that point the crew had "apparently" selected the autothrottle to "climb" mode, which would normally result in a power reduction on both engines. The right throttle lever, however, stayed at the take-off power setting "...as would be the case if [it] had been mechanically prevented due to an unidentified reason from responding to the [ATS servo motor]" (see diagram). Meanwhile, the left throttle lever retarded slowly, taking 42s to reach idle.
The pilot had already begun a 25degrees-bank left turn as required by the departure procedure, but the increasing power asymmetry, says the report, caused the aircraft's 18degree nose-up pitch to decrease to zero, and the bank to increase "...as the aircraft continued to roll over laterally to more than 170degrees to the left, while the pitch seems to have reached 80degrees nose-down."
The report says: "Only small rudder and elevator deflections are recorded [throughout] the event. The data on the digital FDR [flight-data recorder] shows that engine 2 [right-hand throttle] was reduced to idle a few seconds before the end of the recording."
Separately, the Canadian Transportation Safety Board (CTSB) is investigating a 1 March incident in Canadian airspace in which a Tarom A310-300, being flown from Chicago to Amsterdam at 33,000ft, suddenly pulled 1.9g to enter a 30degrees nose-up, 12,000ft/min climb reaching 40,500ft; then plunged through its assigned flight level and finally levelled at 35,000ft . No-one was hurt and the captain continued the flight.
The aircraft the was the same as that which, on a Tarom flight to Paris Orly, had climbed rapidly, stalled and recovered to land safely (Flight International, 5-11 October, P4). Airbus Industrie says: "At this stage, the Canadian authorities have not informed us of any anomalies involving the aircraft's systems."
Source: Flight International
