Heathrow jet crash 'caused by ice'

The Air Accidents Investigation Branch recommended that airlines introduce interim measures for all Boeing 777s to reduce the risk of this happening again.

One passenger suffered a broken leg and eight others received minor injuries when the BA aircraft from Beijing came down short of the runway on January 17.

The cockpit crew were unable to get the required thrust from the engines as the jet approached Heathrow and it landed on the grass just inside the airport's boundary fence.

Co-pilot John Coward, 41, took control for the landing and at a height of about 720ft the thrust of the right engine reduced. About seven seconds later, the thrust of the left engine reduced to a similar level.

The engines continued running but not with the amount of thrust demanded. By 200ft the airspeed had reduced to about 108 knots and the autopilot disconnected at 175ft.

The AAIB released its fifth report into the incident, focusing on the aircraft's fuel system. It concluded: "The investigation has shown that the fuel flow to both engines was restricted - most probably due to ice within the fuel feed system. This ice is likely to have formed from water that occurred naturally in the fuel whilst the aircraft operated for a long period, with low fuel flows, in an unusually cold environment."

Investigators said they had ruled out problems with fuel quality or quantity, the fuel freezing or incorrect procedures by the flight crew as causes of the crash. But they noted that they found distinctive and abnormal marks on the high-pressure fuel pumps from both engines of the BA 777. The experts concluded that these were formed by a phenomenon called "cavitation", which is caused by a restriction in the fuel flow to the pump.

Because there was no evidence of any mechanical obstructions, they concentrated on the possibility of ice building up elsewhere in the fuel system.

Aircraft are designed to cope with significant amounts of the ice crystals which form in fuel when they climb into sub-zero atmospheric conditions. But tests on a Rolls-Royce Trent 800 engine, like that in the BA jet, showed that restricting fuel flow to the high-pressure pump caused a similar effect to that recorded in the accident.