Both engines of the British Airways jet that crash-landed at Heathrow Airport were still running when it came down, investigators have said.
The report said the engine control systems worked as expected
But the engines did not respond sufficiently to a thrust request as the plane came into land, the Air Accident Investigation Branch (AAIB) said.
The AAIB said it was now focusing on the Boeing 777's fuel supply system.
US investigators have noted six previous engine failures in the same type of aircraft, it also emerged.
All 136 passengers and 16 crew on the flight from Beijing survived the crash-landing on 17 January.
The AAIB's investigation update comes as the US National Transportation Safety Board's website listed the previous engine failures.
The most recent was in September 2006, when a Malaysia Airlines' Boeing 777's right engine shut down near Brisbane, Australia.
A UK aviation industry source told the Press Association seven engine failures was "not a large figure" given the aircraft's long flight history.
About 1,000 Boeing 777 jetplanes have been sold since the model's first commercial flight in 1995.
In its update, the AAIB said the Boeing's twin Rolls-Royce engines initially responded to the request for thrust, but after three seconds the thrust of the right engine reduced and after eight seconds there was a thrust reduction in the left one.
Recorded data shows the aircraft had enough fuel and its automatic throttle and engine control systems had worked as expected, the AAIB said.
The AAIB said it was now carrying out a "detailed analysis and examination of the complete fuel flow path from the aircraft tanks to the engine fuel nozzles".