Pilots of an ill-fated TransAsia Airways ATR 72-600 should have aborted its departure from Taipei Songshan airport after noting that a power-control system had not armed, investigators have indicated.
Flight GE235 crashed into the Keelung river shortly after take-off when the crew inadvertently reduced power from its healthy left-hand engine, instead of the right-hand engine which was exhibiting problems.
Taiwanese investigators have disclosed that the aircraft’s automatic take-off power control system (ATPCS) had not initially been armed when the turboprop began its departure roll.
The system provides automatic support – including uptrim and auto-feathering – in the event of an engine failure during take-off.
Investigators probing the fatal 4 February crash, citing flight-recorder data, state that the monitoring pilot, in the right-hand cockpit seat, declared the ATPCS was not armed about 4s into the take-off roll.
In an interview with the inquiry team a TransAsia crew training supervisor said that ATR 72-600 pilots should abort take-off if the ATPCS is not armed during the roll, and that this point was “emphasised” during pilot training.
This requirement to abort is based on there being several procedures to be carried out if the ATPCS is not armed, which are unsuitable to perform during the take-off run.
But the inquiry points out that this policy of aborting is “not clearly described” in any manuals and notices to flight crew. The situation is further complicated by a policy allowing pilots of ATR 72-500s, faced with the same issue, to continue the take-off under certain conditions.
TransAsia flight GE235’s commanding pilot acknowledged the unarmed ATPCS call-out but opted to proceed with the take-off roll.
Just after the standard 70kt speed call, the monitoring pilot exclaimed that the ATPCS had become armed, before the ATR became airborne a few seconds later.
Some 34s into the climb the ATPCS appears to have commanded an uptrim to the left-hand engine, to increase its power, and started auto-feathering the right-hand engine – these actions are the ATPCS system’s normal response to a developing problem in the right-hand powerplant.