Problem with ice in jet's fuel system 'not recognised' - report

Plane safety requirements did not cover the particular ice problem which probably caused a Boeing 777 to crash-land at Heathrow Airport two years ago as the risk was "unrecognised at that time", an official accident report said yesterday.

The crash of the British Airways 777 on January 17 2008 came after the plane lost power due to a restricted fuel flow to both engines, a final report from the Air Accidents Investigation Branch (AAIB) said.

The AAIB concluded it was probable that the engine fuel flow restriction was caused by a build-up of ice within the fuel system on the flight on which 136 passengers were travelling.

The report said it was also probable that ice had formed within the fuel system from water that occurred naturally in the fuel and when fuel temperatures were at a "sticky range" when ice crystals were most likely to adhere to their surroundings.

The AAIB said: "Certification requirements, with which the aircraft and engine fuel system had to comply, did not take account of this phenomenon as the risk was unrecognised at that time."

The report added that research in the 1950s had identified the problem of ice formation in fuel systems from dissolved or entrained (trapped) water but did not identify the scenario of accumulated ice release and subsequent restriction to fuel flow.

The AAIB concluded that the engine component called the fuel oil heat exchanger on the crashed Boeing was susceptible to restriction where presented with soft ice in a high concentration and with a fuel temperature that was below minus 10C.

The AAIB added there were no published guidelines or tests on the susceptibility of a fuel system to ice.

Having lost power, the BA plane, arriving from Beijing, came down within the airfield boundary at Heathrow but 330 metres short of the paved runway, sliding 372 metres before coming to rest.

The left main landing gear (MLG) collapsed and the right MLG separated from the plane. All the passengers were safely evacuated, with one passenger breaking a leg. All told, 34 passengers and 12 cabin crew suffered minor injuries, mainly to the back and neck.

The report said that the cabin crew, led by Captain Peter Burkill, had become aware of a possible engine thrust problem just 43 seconds from touchdown.

Losing speed, the crew tried to increase engine thrust but there was no response from the engines. With a touchdown short of the runway inevitable, a Mayday call put out three second before touchdown.

There was insufficient time for the flight crew to brief the cabin crew or issue a command for passengers to brace themselves, the report said.

There was no fire but there was a significant fuel leak, while there was also an oxygen leak caused by damage to the passenger oxygen bottles from part of the MLG.

The AAIB said some passengers attempted to retrieve personal items during the evacuation.

On November 28, 2008 a Delta Airlines Boeing 777 suffered a similar ice problem while flying over the US, which prompted an investigation by America's National Transportation Safety Board, with the AAIB having an accredited representative.