The Air Accidents Investigation Branch (AAIB) investigation has identified that when the aircraft was at a height of approximately 700 feet, an increase power demand was received at both engine control units. Despite the correct operation of all engine control functions and sufficient fuel on board the aircraft, the engines did not respond.
The focus of the investigation continues to be the fuel system both in the aircraft and on the engines. Under the direction of the AAIB, extensive and challenging full engine testing continues at Rolls-Royce, Derby and some equally, if not more so, challenging fuel system testing is ongoing at Boeing, Seattle, USA.
These tests are collectively aimed at understanding and, if possible, replicating the system/engine performance experienced during the accident.
Fuel experts and statisticians are also involved in the investigation, reviewing and analysing many thousands of data points recorded on the Boeing 777 fleet of aircraft to see if any trends of statistical significance can further contribute to an understanding of the accident.