AAIB Report: Boeing 737-8K5, G-FDZS, 4 March 2024
Boeing 737-8K5 (G-FDZS), insufficient thrust on takeoff, Bristol Airport, 4 March 2024
Graphic of G-FDZS’s takeoff from Bristol Airport. © 2024 Google, Image © 2024 Airbus
When the crew began their takeoff, the autothrottle (A/T) disconnected when the Takeoff/Go-Around switch (TOGA) was selected. As a result, neither thrust lever advanced automatically towards the calculated N1 takeoff setting. Despite attempting to re-engage it, the A/T remained in an inactive mode. The takeoff was conducted with 84.5% N1 instead of 92.8% N1, with the associated reduction in aircraft performance. The rotation occurred close to the end of the runway and the aircraft climb rate was initially very slow. The crew increased power on the engines towards the takeoff setting from 450 ft aal. The rest of the flight to Las Palmas was completed without incident although the A/T remained unavailable. The uncommanded disconnect was likely the result of the voltage being supplied to the autothrottle servo motor (ASM) being too low which was a known problem with the B737 A/T and the older revision of the ASM part fitted to G-FDZS.
The operator has taken a number of safety actions to address both the actions to be taken in the event of an uncommanded disconnection of the A/T at takeoff, and their monitoring of events through flight data monitoring.