Investigations into the fatal TransAsia Airways ATR 72-600 crash into the Keelung river in February last year have concluded that the accident was a result of many contributing factors, but ultimately attributes the disaster to the crew's actions.
In its final report, Taiwan’s Aviation Safety Council says that during the aircraft’s initial climb after takeoff from Taipei Songshan airport, an intermittent discontinuity in the right-hand engine’s auto feather unit (AFU) may have initiated the automatic take-off power control system (ATPCS) sequence, resulting in the autofeather of the right-side engine.
The crew, however, failed to perform the necessary abnormal and emergency procedures to identify and correct the failure. This led the pilot flying to retard the power of the left-hand engine, ultimately shutting it down.
The loss of power and inappropriate flight control inputs generated a series of stall warnings, including the activation of the stick shaker and pusher. Still, the crew failed to immediately recognise the loss of power in both engines, and respond to warnings in-time.
Transcripts derived from the cockpit voice recorder suggest the crew, speaking in a mixture of English and Mandarin, failed to grasp the nature of the situation. There were three people in the cockpit: two captains and a first officer in the jump seat as an observer pilot.
“Had the crew prioritised their actions to stabilise the aircraft flight path, correctly identify the propulsion malfunction… then take actions in accordance with procedure of engine number 2 flame-out at take-off, the occurrence could have been prevented,” says the report.
“Flight crew coordination, communication, and threat and error management were less than effective, and compromised the safety of the flight.”
Besides crew error, investigations also identified other contributing factors such as the airline’s flight operations processes and regulatory oversight of TransAsia by the Civil Aeronautics Administration.
The report adds that the intermittent signal discontinuity in the right engine’s AFU may have caused the ATPCS to not be armed during take-off roll, or was activated during the initial climb, which resulted in a complete ATPCS sequence including autofeathering. Evidence indicated that the discontinuity was likely caused by compromised soldering joints inside the AFU.
The crew also failed to reject the take-off when the power-control system was not armed, and the airline had no clearly documented policies and instructions for this.
Engine-maker Pratt & Whitney has since issued a modification addressing intermittent continuity failure of the AFU, which is being implemented in all new production engines.
The report made 16 safety recommendations to the related organisations.
Flight GE235 crashed into the Keelung River on 4 February 2015 while on a flight to Kinmen from Taipei, killing 43 of the 60 people onboard.