The AAIB, giving details of its initial investigation, said the flight had been normal until the plane made its final approach for landing on Thursday.

The agency said the investigation would now focus on a more detailed analysis of information from the flight recorder and other recorded data, and examination of "the range of aircraft systems" that could affect the engines.
Pilot praised
Captain Peter Burkill, given a rousing reception by staff at the airline's headquarters, declined in a brief statement to make any comment on the cause of the crash.
But he praised his crew for demonstrating "the highest standards of skill and professionalism," thanked the passengers for "their calmness and good sense" and praised the emergency services for reacting speedily.
He said it was John Coward, his co-pilot, who had been at the controls during the difficult last minutes of the flight.
A team of specialists from Boeing arrived to join the air accident investigators, along with experts from Rolls Royce, who are expected to take several months to find the final cause of the crash.
The aircraft was powered by two Rolls-Royce RB211 Trent 895-17 turbofan engines.
Heathrow, the world's busiest international airport, was struggling to return to normal after the crash. 
More than 50 flights were cancelled on Friday morning but British Airways said it planned to operate all its long haul flights and up to 90 per cent of short haul departures.
Gordon Brown, the British prime minister, whose flight to China to promote business ties was delayed by the accident, praised the crew of the airliner.
Speaking shortly after his arrival in Beijing, the Chinese capital, he said: "I think it's right to pay tribute to the calmness and professionalism of the BA staff and the captain, and what he achieved in landing the plane."