While investigators have yet to confirm whether a TransAsia Airways ATR 72 crew mistakenly shut down a healthy engine after the other flamed out, such an error has precedent.
Flight-data recordings show that the aircraft which crashed after departing Taipei Songshan airport on 4 February suffered a power loss in its right-hand Pratt & Whitney PW127 engine. But they also indicate that the throttle lever of the left-hand engine was subsequently retarded and its fuel was shut off.
The aircraft initially continued to climb but began to descend after the left-hand engine was throttled back and the turboprop lost airspeed.
Taiwan’s Aviation Safety Council has disclosed that the aircraft’s stall-warning systems activated after the power loss in both engines.
Three pilots were in the cockpit of the aircraft and the inquiry has yet to provide any details of their conversation which might explain the reasons behind the apparent error.
The aircraft involved was an ATR 72-600, the modernised cockpit of which features digital instrument displays rather than the dials and gauges of its predecessor, the 72-500.
Mistaken identification of a failed engine was behind the fatal crash of a South African Airlink turboprop in September 2009.
The British Aerospace Jetstream 41 came down after the right-hand engine failed on take-off from Durban but the crew – the only occupants – shut down the left-hand powerplant. There were three crew members on board, two of whom survived.
South African Civil Aviation Authority investigators could find “no clear reason” for the crew’s incorrect identification of the failed engine, other than a “complete deviation” from the operator’s standard procedures.
Arguably the most high-profile case involved a British Midland Boeing 737-400 which crashed on approach to the UK’s East Midlands airport in January 1989, after the crew mistakenly shut down the functioning right-hand engine.
The erroneous order to throttle back the operational engine came 19s after the onset of severe vibrations during climb.
UK investigators suggested the crew had acted too quickly, contrary to their training, and that their “rapid reaction” to abnormal engine behaviour resulted in the “incorrect diagnosis”.
More time studying the engine instrument indications, the inquiry added, would have shown clearly which powerplant was causing problems.
Investigators of the TransAsia accident have disclosed that the crew started shutting the throttle lever of the ATR's left engine just 4s after the right-hand engine's flame-out warning.
The inquiry has yet to determine the reason for the initial right-hand flame-out, as indicated on the flight-data recording.
Pilots of the ATR received an initial caution about the right-hand engine at an altitude of around 1,300ft, some 90s after flight GE235 was cleared for departure to Kinmen.
Flight-data recordings indicate that the aircraft continued to ascend to around 1,700ft before a descent lasting around 1min 20s, ending when the turboprop struck an overpass and crashed into a river.
Source: Cirium Dashboard
