TransAsia Airways

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 flight crew did not comply with the published runway 20 VOR non-precision instrument approach procedures at Magong Airport with respect to the minimum descent altitude (MDA). The captain, as the pilot flying, intentionally descended the aircraft below the published MDA of 330 feet in the instrument meteorological conditions (IMC) without obtaining the required visual references.
- The aircraft maintained an altitude between 168 and 192 feet before and just after overflying the missed approach point (MAPt). Both pilots spent about 13 seconds attempting to visually locate the runway environment, rather than commencing a missed approach at or prior to the MAPt as required by the published procedures.
- As the aircraft descended below the minimum descent altitude (MDA), it diverted to the left of the inbound instrument approach track and its rate of descent increased as a result of the flying pilot’s control inputs and meteorological conditions. The aircraft’s hazardous flight path was not detected and corrected by the crew in due time to avoid the collision with the terrain, suggesting that the crew lost situational awareness about the aircraft’s position during the latter stages of the approach.
- During the final approach, the heavy rain and associated thunderstorm activity intensified producing a maximum rainfall of 1.8 mm per minute. The runway visual range (RVR) subsequently reduced to approximately 500 meters. The degraded visibility significantly reduced the likelihood that the flight crew could have acquired the visual references to the runway environment during the approach.
- Flight crew coordination, communication, and threat and error management were less than effective. That compromised the safety of the flight. The first officer did not comment about or challenge the fact that the captain had intentionally descended the aircraft below the published minimum descent altitude (MDA). Rather, the first officer collaborated with the captain’s intentional descent below the MDA. In addition, the first officer did not detect the aircraft had deviated from the published inbound instrument approach track or identify that those factors increased the risk of a controlled flight into terrain (CFIT) event.
- None of the flight crew recognized the need for a missed approach until the aircraft reached the point (72 feet, 0.5 nautical mile beyond the missed approach point) where collision with the terrain became unavoidable.
- The aircraft was under the control of the flight crew when it collided with foliage 850 meters northeast of the runway 20 threshold, two seconds after the go around decision had been made. The aircraft sustained significant damage and subsequently collided with buildings in a residential area. Due to the high impact forces and post-impact fire, the crew and most passengers perished.
- According to the flight recorders data, non-compliance with standard operating procedures (SOP's) was a repeated practice during the occurrence flight. The crew’s recurring non-compliance with SOP's constituted an operating culture in which high risk practices were routine and considered normal.
- The non-compliance with standard operating procedures (SOP's) breached the obstacle clearances of the published procedure, bypassed the safety criteria and risk controls considered in the design of the published procedures, and increased the risk of a controlled flight into terrain (CFIT) event.

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.

The following findings were identified:
1. The accident flight encountered severe icing conditions. The liquid water content and maximum droplet size were beyond the icing certification envelope of FAR/JAR 25 appendix C.
2. TNA's training and rating of aircraft severe icing for this pilots has not been effective and the pilots have not developed a familiarity with the Note, CAUTION and WARNING set forth in Flight Crew Operating Manual and Airplane Flight Manual to adequately perform their duties.
3. After the flight crew detected icing condition and the airframe de-icing system was activated twice, the flight crew did not read the relative Handbook, thereby the procedure was not able to inform the flight crew and to remind them of "be alert to severe icing detection".
4. The "unexpected decrease in speed" indicated by the airspeed indicator is an indication of severe icing.
5. The flight crew did not respond to the severe Icing conditions with pertinent alertness and situation awareness that the aircraft might have encountered conditions which was "outside that for which the aircraft was certificated and might seriously degrade the performance and controllability of the aircraft".
6. The flight crew was too late in detecting the severe icing conditions. After detection, they did not change altitude immediately, nor take other steps required in the Severe Icing Emergency Procedures.
7. The aircraft was in an "unusual or uncontrolled rolling and pitching" state, and a stall occurred thereafter.
8. After the aircraft had developed a stall and an abnormal attitude, the recovery maneuvering did not comply with the operating procedures and techniques for Recovery of Unusual Attitudes. The performance and controllability of the aircraft may have been seriously degraded by then. It cannot be confirmed whether the unusual attitudes of the aircraft could have been recovered if the crew's operation had complied with the relevant procedures and techniques.
9. During the first 25 minutes, the extra drag increased about 100 counts, inducing a speed diminishing about 10 knots.
10. During the airframe de-icing system was intermittently switched off, it is highly probable that residual ice covered on the wings of the aircraft.
11. Four minutes prior to autopilot disengaged, the extra drag increased about 500 counts, and airspeed decayed to 158 knots, and lift-drag ratio loss about 64% rapidly.
12. During the 10s before the roll upset, the longitudinal and lateral stability has been modified by the severe ice accumulated on the wings producing the flow separation. Before autopilot disengaged, the aerodynamic of the aircraft (lift/drag) was degraded of about 40%.

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.