Turkish Airlines accident report released
Contributors are not employed, compensated or governed by TD, opinions and statements are from the contributor directly
A faulty altimetre was to blame for the accident involving a Turkish Airlines aircraft at Amsterdam’s Schiphol Airport on Wednesday 25 February 2009.
A final report on the incident, which involved the TC-JGE registered aircraft, which was travelling from Istanbul to the Dutch city and crashed on landing, has been released.
The Dutch Safety Board released the document on 6 May, and has identified how the event happened, and what could be done in future to prevent such accidents.
Turkish Airlines provided the following comments on the report:
The aircraft had two radio altimeter systems to measure its vertical distance from the ground. During the approach of TC-JGE aircraft into Amsterdam Schiphol Airport’s runway 18R, the right-hand radio altimeter system used by the First Officer, who was flying the aircraft, was performing normally, while the left-hand system showed an incorrect altitude of -8ft. The aircraft was designed so that the autothrottle system, which is the part of autoflight system that controls the speed of aircraft by altering engine power, receives the data on ground proximity only from the left-hand radio altimeter system without any comparison with the right-hand system’s data, and the autothrottle system accepted the left-hand system’s incorrect altitude information as an indication that the aircraft was at the touchdown stage of landing. The autothrottle system reduced the engine power, causing the aircraft speed to go below the minimum speed needed to keep the aircraft controllable in the air (the stall speed), and the resulting loss of control of the aircraft occurred at an altitude too close to the ground for recovery. This error-prone relationship between the autothrottle and left-hand radio altimeter system had not been previously explained in the aircraft manufacturer’s documentation for the flight crews; this was described in an update only after this accident.
Because Amsterdam Air Traffic Control brought the aircraft in with a shorter -than -normal approach route, the aircraft was flying higher and faster than usual. Due to this attitude and speed, it was to be expected that the thrust levers would go to the idle position to reduce engine power as the aircraft was slowing down and descending to reach normal approach speeds and altitudes. This appropriate expectation prevented the system error from being realized in time. As the speed approached the required minimum controllable speed, aural and visual warning systems were activated, and the crew immediately initiated steps to recover control of the aircraft. But the prompt advancement of the thrust levers by the flight crew was initially counteracted by the autothrottle system, which retarded the thrust levers again. The crew disengaged the autothrottle and advanced the thrust levers again, but the loss of time due to this system behavior in close proximity to the ground resulted in the recovery efforts being unsuccessful. The aircraft manufacturer’s documents had previously advised the pilots of the need to advance the thrust levers immediately, but the documents had not mentioned the need to disconnect the autothrottle system during such a recovery.
Comments are closed.