Further details concerning last week”s undershoot by a British Airways Boeing 777-200 have been released by the UK Air Accidents Investigation Branch (AAIB).
The 777 landed in a grassy area short of London Heathrow”s runway 27L last Thursday (17 January), with all 136 passengers and 16 crew managing to evacuate with only minor injuries.
The AAIB has been concentrating its efforts on why neither Rolls-Royce Trent 895 engine responded to throttle lever inputs during final approach. Pictures taken from a mobile phone show the 777 with an unusually high nose-up attitude shortly before descending onto the boggy grass with extensive scarring marks clearly visible on the ground as the right hand main landing gear detached and the left counterpart pushed up through the wing root.
A statement from the AAIB says: ”While the aircraft was stabilised on the ILS [Instrument Landing System] approach with the autopilot engaged, the autothrust system commanded an increase in thrust from both engines.
”The engines both initially responded, but after around 3s, the thrust of the right engine reduced. Some 8s later, the thrust reduced on the left engine to a similar level. The engines did not shut down and both continued to produce thrust at an engine speed above flight idle, but less than the commanded thrust.”
The AAIB says it has issued the update as it is: ”sensitive to the needs of the industry, including Boeing, Rolls-Royce, BA and other 777 operators and crews.”
But the AAIB confines itself to noting that ”all possible scenarios” could account for the reduction in thrust and the continued lack of response to throttle lever inputs.
What is interesting is that the AAIB maintains there was sufficient fuel on board the 777 and that autothrottle and engine control commands were performing ”as expected prior to and after, the reduction in thrust.”
BA says that aircraft are now landing normally on runway 27L. Following the incident, aircraft were able to depart on the foreshortened runway but not land as the 150t 777 had to be moved to an apron area.