The UK Air Accidents Investigation Branch (AAIB) has released a Special Bulletin concerning the failure of the auto throttle on a Boeing 737-800.
The incident involving the TUI Airways Boeing 737-800 aircraft registered G-FDZS occurred on takeoff from Bristol Airport, 4 March 2024.
The Special Bulletin contains preliminary information on this serious incident. It provides information for pilots and operators of the Boeing 737 Next Generation (737NG) about the A/T disengage occurrence in this event.
It concludes with the actions the manufacturer expects crews to take should such a disengagement occur.
History of the flight
The aircraft was prepared for a flight from Bristol Airport to Las Palmas, Gran Canaria. It was operating with six crew and 163 passengers.
The TUI Boeing 737-800 completed a takeoff from Runway 09 at Bristol Airport with insufficient thrust to meet regulated performance.
The autothrottle (A/T) disengaged when the takeoff mode was selected, at the start of the takeoff roll. Subsequently, the thrust manually set by the crew (84.5% N1) was less than the required takeoff thrust (92.8% N1).
Neither pilot then noticed that the thrust was set incorrectly. The error was not picked up through the standard operating procedures (SOPs).
As a result, G-FDZS became airborne 260 m from the end of Runway 09. The aircraft then overflew the runway end at a height of approximately 10 ft.
Further, the correct thrust setting was not set until passing approximately 900 ft aal. This resulted in the A38 road, adjacent to the boundary of Bristol Airport, being overflown at less than 100 ft.
Analysis
The TUI Airways aircraft took off from Runway 09 with an incorrect thrust setting. It was significantly below that required to achieve the correct takeoff performance.
Rotation for the takeoff occurred only 260 m before the end of the runway. As a result, the aircraft passed over the end at a height of approximately 10 ft.
The N1 required to achieve the required takeoff performance was 92.8% but, following an A/T disconnect when the crew selected TOGA, 84.5% was manually set instead.
Despite an SOP requirement to check the thrust setting on takeoff, the crew did not realise that the thrust was not set correctly until after the takeoff although they had noted how close to the end of the runway they were.
The A/T had disconnected when the TOGA switch was pressed due to a fault with the ASM associated with the thrust lever for engine 1.
This disconnect was a known issue with the older type ASMs fitted to the aircraft type.
The manufacturer has issued a Fleet Team Digest for operators detailing the issue and the SB for replacing the ASMs with a newer model.
The investigation continues to examine all pertinent factors associated with this serious incident and a final report will be issued in due course.
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