Takeoff (climb)

A total loss of engine power due to the refueler's incorrect refueling of the airplane. Contributing to the accident was the fixed-base operator's improper fueling nozzle, which facilitated the use of an incorrect fuel, and the pilot's inadequate preflight inspection.

The engine failure was caused by damage to the engine's power turbine section. Most likely, the damage has been initiated in a labyrinth seal to the power turbine. The cause of the initial damage of the seal has not been established. The technical failure can not be assessed to be in a risk category where the risk of repeated failures of the same type is high. The accident was caused by damage to the power turbine which occurred over time, and that could not be identified by the engine's maintenance program.

The left engine propeller's uncommanded travel to the feathered position during takeoff for reasons that could not be determined due to impact damage. Contributing to the accident was the flight crew's failure to establish a coordinated climb once the left engine was shut down and the left propeller was in the feathered position.

The accident was the result of many contributing factors which culminated in a stall-induced loss of control. During the initial climb after takeoff, an intermittent discontinuity in engine number 2’s auto feather unit (AFU) may have caused the automatic take off power control system (ATPCS) sequence which resulted in the uncommanded autofeather of engine number 2 propellers. Following the uncommanded autofeather of engine number 2 propellers, the flight crew did not perform the documented abnormal and emergency procedures to identify the failure and implement the required corrective actions. This led the pilot flying (PF) to retard power of the operative engine number 1 and shut down it ultimately. The loss of thrust during the initial climb and inappropriate flight control inputs by the PF generated a series of stall warnings, including activation of the stick shaker and pusher. After the engine number 1 was shut down, the loss of power from both engines was not detected and corrected by the crew in time to restart engine number 1. The crew did not respond to the stall warnings in a timely and effective manner. The aircraft stalled and continued descent during the attempted engine restart. The remaining altitude and time to impact were not enough to successfully restart the engine and recover the aircraft.
The following findings related to probable causes were noted:
An intermittent signal discontinuity between the auto feather unit (AFU) number 2 and the torque sensor may have caused the automatic take off power control system (ATPCS):
- Not being armed steadily during takeoff roll,
- Being activated during initial climb which resulted in a complete ATPCS sequence including the engine number 2 autofeathering.
The available evidence indicated the intermittent discontinuity between torque sensor and auto feather unit (AFU) number 2 was probably caused by the compromised soldering joints inside the AFU number 2.
The flight crew did not reject the take off when the automatic take off power control system ARM pushbutton did not light during the initial stages of the take off roll.
TransAsia did not have a clear documented company policy with associated instructions, procedures, and notices to crew for ATR72-600 operations communicating the requirement to reject the take off if the automatic take off power control system did not arm.
Following the uncommanded autofeather of engine number 2, the flight crew failed to perform the documented failure identification procedure before executing any actions. That resulted in pilot flying’s confusion regarding the identification and nature of the actual propulsion system malfunction and he reduced power on the operative engine number 1.
The flight crew’s non-compliance with TransAsia Airways ATR72-600 standard operating procedures - Abnormal and Emergency Procedures for an engine flame out at take off resulted in the pilot flying reducing power on and then shutting down the wrong engine.
The loss of engine power during the initial climb and inappropriate flight control inputs by the pilot flying generated a series of stall warnings, including activation of the stick pusher. The crew did not respond to the stall warnings in a timely and effective manner.
The loss of power from both engines was not detected and corrected by the crew in time to restart an engine. The aircraft stalled during the attempted restart at an altitude from which the aircraft could not recover from loss of control.
Flight crew coordination, communication, and threat and error management (TEM) were less than effective, and compromised the safety of the flight. Both operating crew members failed to obtain relevant data from each other regarding the status of both engines at different points in the occurrence sequence. The pilot flying did not appropriately respond to or integrate input from the pilot monitoring.
The engine manufacturer attempted to control intermittent continuity failures of the auto feather unit (AFU) by introducing a recommended inspection service bulletin at 12,000 flight hours to address aging issues. The two AFU failures at 1,624 flight hours and 1,206 flight hours show that causes of intermittent continuity failures of the AFU were not only related to aging but also to other previously undiscovered issues and that the inspection service bulletin implemented by the engine manufacturer to address this issue before the occurrence was not sufficiently effective. The engine manufacturer has issued a modification addressing the specific finding of this investigation. This new modification is currently implemented in all new production engines, and another service bulletin is available for retrofit.
Pilot flying’s decision to disconnect the autopilot shortly after the first master warning increased the pilot flying’s subsequent workload and reduced his capacity to assess and cope with the emergency situation.
The omission of the required pre-take off briefing meant that the crew were not as mentally prepared as they could have been for the propulsion system malfunction they encountered after takeoff.

The accident was due to a loss of control that brought the aircraft into unusual attitudes, which the pilot was unable to restore and which led to his fall. The insufficient skills of the pilot when faced with a high performance aircraft, whose systems are complex, contributed to the occurrence of the accident.

The Aircraft Accident Investigation and Inquiry Board determined that the probable cause of this accident was:
- Lack of recurrent training of the flight crew:
Routine flights do not prepare a pilot for unusual situations, whether they are unexpected crosswinds or systems/engine anomalies. Pilots should receive regular recurrent training to include abnormal and emergency procedures.
- The existing runway edge light design:
The PIC tried to recover the aircraft back to the runway but apparently the aircraft left main landing gears already hit or bumped the concrete base of runway edge lights. The design of runway strips or shoulder must be free from fixed objects other than frangible visual aids provided for the guidance of aircraft and must not be constructed
with sharp edges; and where the lights will not normally come into contact with aircraft wheels, such as threshold lights, runway end lights and runway edge lights;
- Human Factors:
Due to deteriorating adverse weather conditions and due to the delay of their initial request for take-off clearance plus the sudden change of flight plan affected the Captain’s ability to perform a take-off procedure as recommended in the aircraft flight manual and instead delegated flight control duties to the F/O resulting in the loss of coordination between the light crew.

The accident occurred as result of the aircraft departing the side of the runway after the commander rejected takeoff after having been unable to use the elevator because of the yoke's locked position. The roll beyond the edge of the runway was likely caused by the flight engineer while attempting to operate the handle to release the flight controls lock while the aircraft was already accelerating for takeoff. The accident was thus caused by this combination of factors:
- violation of requirements by FCOM to ascertain the flight controls were free and usable before engine start,
- failure by the crew to execute the checklists to check elevator, rudder and ailerons were free to move before takeoff,
- flight crew receives insufficient practice in real flight to maintain skills acquired during simulator training in the management of the aircraft and its systems resulting in negative impact during emergency situations.

During the attempted takeoff, the rudder was central from 40 kt and remained so until approximately 65 kt. Between approximately 52 and 65 kt, the aircraft turned right slightly before it turned left sharply at approximately 65 kt. Given that the rudder was central, this change of direction might have been caused by one, or a combination of the following factors:
a. Differential braking
b. Asymmetric thrust
c. A change in wind speed and direction
d. A nose wheel steering input
Data from the FDR showed that thrust was applied symmetrically throughout the takeoff run, and the manufacturer did not consider that the data for longitudinal acceleration and indicated airspeed supported the use of differential braking.