Heathrow BA plane crash caused by 'unknown' ice fault
Everyone on board the plane escaped without serious injury
The fault which caused a plane to crash land at Heathrow Airport was not covered by plane safety requirements at the time, an official report has said.
The British Airways (BA) Boeing 777 lost power to both engines because of restricted fuel flow, the Air Accidents Investigation Branch (AAIB) said.
It said the crash, on 17 January 2008, was probably caused by a build-up of ice in the fuel system.
None of the 152 people on board the aircraft was seriously injured.
The report said ice had probably formed within the fuel system from water that occurred naturally in the fuel.
It added that when fuel temperatures were in a "sticky range", ice crystals were most likely to stick to their surroundings.
The AAIB report 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 trapped water, but it did not identify that it was possible for accumulated ice to restrict fuel flow.
Tom Symonds, Transport correspondent
The incident was remarkable for the lack of a fire following the crash, which ruptured the plane's fuel tanks. This would have caused far more risk to the passengers.
But investigators also say the build up of ice and loss of power resulted from a unique set of circumstances.
British Airways praised Captain Peter Burkill and First Officer John Coward, and awarded them the airline's Safety Medal.
They did not have time to do much, but Peter Burkill added 51 valuable metres to the flight by changing a flap setting, and John Coward successfully kept control of an stalling aircraft.
Indeed some of the passengers interviewed by the BBC, had not realised what had happened until they were ordered to evacuate. To them, it had just seemed like a "hard landing".
The AAIB concluded that an engine component, called the fuel oil heat exchanger, on the crashed Boeing was likely to stop working in a combination of soft ice and with a fuel temperature below -10C (14F).
The report 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 330m (1,080ft) short of the paved runway, sliding 372m (1,220ft) before coming to rest.
Everyone was safely evacuated from the aircraft, with one passenger breaking a leg.
The report said the 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.
A mayday call put out three seconds before touchdown.
Flight Captain Peter Burkill: "I thought I was going to die"
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.
The AAIB said some passengers attempted to retrieve personal items during the evacuation.
On 28 November 2008 a Delta Airlines Boeing 777 suffered a similar ice problem while flying over the USA, which prompted an investigation by America's National Transportation Safety Board, with the AAIB having an accredited representative.
The AAIB has made 18 safety recommendations following the two incidents
Boeing and Rolls-Royce, which makes aircraft engines, said they had taken steps to prevent the ice phenomenon from recurring.
The AAIB has now made nine further safety recommendations, including some which address plane "crashworthiness", which test the ability of an aircraft to withstand an accident.
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