The Aviation Safety Council (ASC) released its final report on investigation of a TransAsia Airways (TNA) ATR72-600 aircraft, registration number B-22816, loss of control and crashed into Keelung River three nautical miles east of Songshan Airport.
On February 4, 2015, about 1054 Taipei Local Time, TransAsia Airways (TNA) flight GE 235, an ATR-GIE Avions de Transport Régional ATR72-212A (ATR72-600) aircraft, registered B-22816, experienced a loss of control during initial climb and impacted Keelung River, three nautical miles east from its departing runway 10 of Taipei’s Songshan Airport. Forty-three occupants were fatally injured, including three flight crew, one cabin crew, and 39 passengers. The remaining 13 passengers and one cabin crew sustained serious injuries. One passenger received minor injuries. The aircraft was destroyed by impact forces. The aircraft’s left wing tip collided with a taxi on an overpass before the aircraft entered the river. The taxi driver sustained serious injuries and the only taxi passenger sustained minor injuries. Flight 235 was on an instrument flight rules (IFR) regular public transport service from Songshan to Kinmen.
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.
Had the crew prioritized their actions to stabilize the aircraft flight path, correctly identify the propulsion system malfunction which was the engine number 2 loss of thrust and then take actions in accordance with procedure of engine number 2 flame out at take off, the occurrence could have been prevented. The investigation report identified a range of contributing and other safety factors relating to the engine’s auto feather unit, crew of the aircraft, TransAsia’s flight operations and management processes, and the regulatory oversight of TransAsia by the Civil Aeronautics Administration (CAA).
This investigation identified important learning opportunities for pilots, operators, regulatory agencies and aircraft manufacturer to improve future aviation safety and to seek to ensure such an accident never happens again. The Aviation Safety Council (ASC) has issued a series of safety recommendations to TransAsia Airways, CAA and aircraft/engine/component manufacturers to correct the serious safety deficiencies identified during the investigation. The manufacturers of aircraft, engine and auto feather unit have also implemented various safety actions in response to the occurrence.
Findings Related to Probable Causes
- 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 takeoff roll.
- TransAsia Airways 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.
Findings Related to Risk
- 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.
Airline Safety Management
- TransAsia Airways (TNA) did not follow its own procedures when selecting and training pilot flying for upgrade. The TNA’s quality assurance processes had not detected that the command selection upgrade process had been compromised.
- TransAsia Airways (TNA) did not use widely available crew resource management (CRM) guidelines to develop, implement, reinforce, and assess the effectiveness of their flight crew CRM training program.
- While the TransAsia Airways (TNA) ATR72-600 differences training program was consistent with the European Aviation Safety Agency ATR72 operational evaluation board report and compliant from a Civil Aeronautics Administration regulatory perspective, it may not have been sufficient to ensure that TNA flight crews were competent to operate the ATR72-600 under all normal procedures and a set of abnormal conditions.
- The ATR72-600 differences training records for the GE 235 flight crew showed that Captain A probably needed more training on the single engine flame out at take off procedure. That meant if the differences training records were stored, adequately maintained and evaluated by appropriate TransAsia Airways (TNA) flight operations and/or quality assurance personnel, the TNA would have had yet another opportunity to review Captain A’s ability to handle engine out emergencies.
- Captain A’s performance during the occurrence was consistent with his performance weaknesses noted during his training, including his continued difficulties in handling emergency and/or abnormal situations, including engine flame out at take off and single engine operations. However, TransAsia Airways did not effectively address the evident and imminent flight safety risk that Captain A presented.
- The Civil Aeronautics Administration’s (CAA) oversight of flight crew training, including crew resource management (CRM) training, is in need of improvement.
- The systemic TransAsia Airways (TNA) flight crew non-compliances with standard operating procedures identified in previous investigations, including GE 222, remained unaddressed at the time of the GE235 occurrence. Although the Civil Aeronautics Administration (CAA) had conducted a special audit after the GE 222 accident which identified the standard operating procedures compliance issue, the CAA did not ensured that TNA responded to previously identified systemic safety issues in a timely manner to minimize the potential risk.
- The flight crew were certificated and qualified in accordance with Civil Aeronautics Administration (CAA) regulations and company requirements. There was no evidence to indicate that the flight crew’s performance might have been adversely affected by pre-existing medical conditions, fatigue, medication, other drugs or alcohol during the occurrence flight.
- Visual meteorological conditions (VMC) prevailed at the time of the aircraft’s departure. No adverse weather conditions were present for the flight.
- The aircraft’s certificate of airworthiness and registration were current at the time of the occurrence. The occurrence aircraft was dispatched at Songshan Airport with no known defects and was in compliance with all applicable airworthiness directives and service bulletins. A review of the aircraft’s maintenance records before the occurrence flight revealed that there were no defects reported that related to engine number 2 automatic feathering system.
- Flight crew transferred from conventional flight instruments to a more advanced avionic suite with primary flight display, the visual pattern and information picked up by the crew in an emergency situation may not be retrieved at the same location with the same display.
- Although the influence of the flight director indication was not demonstrated in the occurrence flight and the logics of ATR flight director bars are consistent with other aircraft types within the industry, the simulator flight illustrated the flight director bars indication during stall warning were in contradiction with the automatic stall protection inputs and thus may disturb the crew.
- The ATR72 formal document has no general statement of rejecting take off policy and procedure of rejecting take off with both engines operative.
Investigators asked TransAsia Airways to conduct a thorough review of the airline’s flight crew training programs, including recurrent training, crew resource management (CRM) training, upgrade training and differences training. The airline should also improve internal monitoring mechanisms on safety, training and pilot performance, they investigators said.
TransAsia said in a statement it respects the report’s findings, and has taken steps since last year to improve safety and crew training.