Taipei-Songshan

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.

After completing the aerial photogrammetry of Morakot No.16 measuring line, the aircraft turned 280 degrees to the right and attempted to climb to get out of the valley area. During climbing, the pitch of the aircraft was remained more than 20 degrees for a few seconds, the aircraft might nearly close to stall and activated stall warning. The aircraft performance might not be able to fly over the obstacles ahead under this condition, the aircraft flew into trees and crashed. When completing the aerial photography of Morakot No.16 measuring line from the north to the south, the aircraft could not be able to fly over mountains ahead between the direction of 9 to 3 o’clock with the aircraft best climb performance. Despite the available climbing distance was longer when flight crew chose to turn to the right, the area geography was not favorable for circling climb or turn around to escape the mountain area safely. The on board personnel choose to perform an aerial photogrammetry at Morakot when weather condition was permitted after completing the aerial photography at Wanrong Woods without any advance planning due to the Morakot aerial photography had been behind schedule.

Inadequate planning and implementation in airport construction safety procedures by both the CAA and the military authority, inadequacy in landing approval when exceeding the curfew hour, insufficient cooperation and coordination between the CAA and the military base authorities prior to construction work, lack of awareness to a lit runway when entering an active runway without acknowledging the tower controllers.

A flammable liquid (gasoline) inside bleach and softener bottles and sealed with silicone was carried on board the aircraft. A combustible vapor formed as the leaking gasoline filled the stowage bin, and the impact of the landing aircraft created a short in a battery. The short ignited the gasoline vapor and created the explosion. Contributing factors to the accident were:
- The Civil Aeronautical Administration Organic Regulations and its operational bylaws fail to designate any entity as responsible for hazardous materials;
- The Aviation Police fail to properly recruit and train personnel, to include preparing training materials and evaluating training performance. Some new recruits were found to have not received any formal security check training, but instead were following instructions from senior inspectors. Consequently, new inspectors cannot be relied upon to identify hazardous materials;
- The detectors and inspectors failed to detect the hazardous materials. The detectors used by the Aviation Police did not detect the banned motorcycle batteries, nor did security inspectors detect the liquid bleach, a banned corrosive substance.

Wrong approach configuration on part of the crew who continued the descent under VFR mode in IMC conditions, below the MDA until the aircraft struck the water surface. Poor supervision on part of the captain. Poor crew coordination and poor approach and landing planning.

The crew failed to adhere to the published approach procedures and continued the descent below MDA until the aircraft struck the ground. Brand new, the aircraft was delivered to TransAsia Airways last December 20 and was equipped with a category II GPWS. It is believed that the GPWS alarm did not sound in the cockpit and was not recorded on the CVR.

The fan cowl on the left engine separated during initial climb.