What happened
On October 18, 2004, TransAsia Airways Flight 536, an Airbus A320-232 with registration B-22310, was performing a landing at Taipei Sungshan Airport during heavy rain conditions. As the aircraft touched down, the crew attempted to decelerate using various systems; however, the aircraft failed to stop within the runway limits. The aircraft overran the runway, exiting the paved surface and entering a muddy area. During the excursion, the nose landing gear struck a drainage ditch, causing the sliding tube to break, and both engine nacelles made contact with the ground. There were no fatalities and no serious injuries reported among the passengers and crew.
The investigation
The investigation focused on the aircraft's deceleration performance and the crew's management of the thrust levers. Investigators examined the flight data recorder (FDR) and cockpit voice recorder (CVR) to reconstruct the sequence of events. Key areas of study included the activation of the ground spoilers, the effectiveness of the braking system, and the status of the thrust reversers. Technical analysis by Airbus revealed that the autothrust system disconnected unexpectedly due to an operational discrepancy between the two thrust levers. Specifically, while one lever was moved into the reverse range, the other remained in a position that caused an EPR target comparison error, leading to an involuntary disconnection of the autothrollle system. This left the engine thrust frozen at a higher power setting than intended.
Findings
- The primary cause of the overrun was the involuntary disconnection of the autothrust system, which left the thrust on engine 2 frozen at a higher power setting (CLB notch) while the crew was attempting to decelerate.
- The aircraft was operating in heavy rain, which resulted in a wet runway surface and increased the required stopping distance.
- The crew's use of the thrust levers caused a mismatch in the FADEC EPR target feedback, triggering the autothrust disconnection warning and subsequent loss of thrust control.
- The ground spoilers were not deployed, which significantly reduced the aircraft's ability to decelerate effectively on the wet surface.