Ice crystals in the jet fuel were blamed as the cause of the accident, clogging the fuel/oil heat exchanger (FOHE) of each engine.

[4](p155)[4](p149) The first symptoms of the fuel-flow restriction were noticed by the flight crew at an altitude of 720 feet (220 m) and 2 miles (3.2 km) from touchdown, when the engines repeatedly failed to respond to a demand for increased thrust from the autothrottle.

In attempting to maintain the instrument landing system glide slope, the autopilot sacrificed speed, which reduced to 108 knots (200 km/h; 124 mph) at 200 feet (61 m).

[4](p139)[12] At 12:42, the 777 passed just above the residential street of Myrtle Avenue,[13] then immediately after overflew traffic on the A30 and the airport's Southern Perimeter road and landed on the grass about 270 metres (890 ft) short of runway 27L.

The decision to raise the flaps allowed the plane to glide beyond the ILS beacon within the airport perimeter, thus avoiding more substantial damage.

[4](pp160-163) The right main landing gear also penetrated the cabin space, causing the sole serious injury in this accident to a passenger in seat 30K.

The left main gear was pushed up through the wing, as it was designed to do in case of failure due to excessive vertical load.

[14] Willie Walsh, the British Airways chief executive, released a statement praising the actions of the "flight and cabin crew [who] did a magnificent job and safely evacuated all of the 136 passengers ...

In an attempt to minimise further travel disruptions, Heathrow Airport received dispensation from the Department for Transport to operate some night flights.

[19] During a press conference the day after the accident, Captain Peter Burkill said that he would not be publicly commenting on the cause of the incident while the AAIB investigation was in progress.

[22] Burkill subsequently established a blog and wrote a book, Thirty Seconds to Impact, that denounced BA's treatment of the situation following the crash.

In my opinion, British Airways is the pinnacle of any pilot's career, and it is my honour and privilege to be returning to an airline that I joined as a young man.

[28] An electronic or software glitch in the computerised engine-control systems was suggested as possible causes of the simultaneous loss of power on both engines.

[4](pp145-146) Initial analysis from David Learmount, a Flight International editor, was that "The aircraft had either a total or severe power loss and this occurred very late in the final approach because the pilot did not have time to tell air traffic control or passengers."

[35] The information downloaded from these devices confirmed what the crew had already told the investigators, that the engines had not responded when the throttles were advanced during final approach.

The report noted the aircraft had flown through air that was unusually cold (but not exceptionally so), and concluded that the temperature had not been low enough to freeze the fuel.

This included creating a mock-up of G-YMMM's fuel delivery system, to which water was added to study its freezing properties.

As temperatures in flight had not dropped below the 777's designed operating parameters, the AAIB recommended Boeing and Rolls-Royce take interim measures on Trent 800-powered 777s to reduce the risk of ice restricting fuel delivery.

[40] The report acknowledged that a redesign of the fuel system would not be practical in the near term, and suggested two ways to lower the risk of recurrence.

[4](p145) The Special Bulletin of 12 May 2008 specifically ruled out certain other possible causes, stating: "There is no evidence of a wake vortex encounter, a bird strike, or core engine icing.

The investigation identified the following probable causal factors that led to the fuel flow restrictions: The AAIB also studied the crashworthiness of the aircraft during the accident sequence.

The report recommended that Boeing redesign the landing gear attachment to reduce the likelihood of fuel loss in similar circumstances.

The report restated a previous Boeing Service Bulletin giving procedural advice that fuel switches should be operated before fire handles.

[1] On 26 November 2008, Delta Air Lines Flight 18 from Shanghai to Atlanta, another Trent 800-powered Boeing 777, experienced an "uncommanded rollback" of one engine while in cruise at 39,000 feet (12,000 m).

In early 2009, Boeing sent an update to aircraft operators, linking the British Airways and Delta Air Lines "uncommanded rollback" incidents, and identifying the problem as specific to the Rolls-Royce engine FOHEs.

[44] The enquiries led Boeing to reduce the recommended time that the fuel on 777 aircraft equipped with Rolls-Royce Trent 800-series engines be allowed to remain at temperatures below −10 °C (14 °F) from three to two hours.

[45] On 11 March 2009, the NTSB issued urgent safety recommendation SB-09-11 calling for the redesign of the FOHEs used on Rolls-Royce Trent 800 Series engines.

[44] In November 2009, 10 passengers were announced to be suing Boeing over the incident in the Circuit Court of Cook County in Illinois, United States.