Several different theories have been put forward as to what caused the jet to crash-land on its approach to Heathrow. Ben Webster examines them:

Bird strike Very unlikely because the pilots did not report seeing any birds or hearing them strike the engines.

Lack of fuel Very unlikely. A BA source says the plane landed with more than ten tonnes of fuel, more than normal after a 12-hour flight.

Fuel contamination: Unlikely because there had been no reported problems during the flight.

Electrical failure Possible, but systems are duplicated in case of failure. The engines have separate fuel tanks, pumps and supply systems so a problem with one should not result in both failing.

Pilot error Possible - the AAIB final report may conclude that the pilots could have responded to warning signals differently.

What happens now? The Air Accidents Investigation Branch yesterday successfully downloaded the black boxes: the flight data recorder, cockpit voice recorder and quick access recorder. The data recorder captures data second-by-second on the performance of key instruments and systems in the critical final stages of the flight.

Was there any earlier warning that something was wrong? The AAIB’s initial report says: “Initial indications from the interviews and flight recorder analyses show the flight and approach to have progressed normally until the aircraft was . . . approximately 600 ft and 2 miles from touchdown.”

When was the last crash at Heathrow? On June 18, 1972, a British European Airways plane crashed within three minutes of taking off, claiming 188 lives. The Trident jet came down in a field near Staines after the crew of the aircraft failed to maintain the correct speed after take-off. It missed the town centre by a few hundred yards.

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