Crashed jet's ice problem 'not previously recognised'
Aircraft safety requirements did not cover the particular ice problem that probably caused a Boeing 777 to crash-land at London's Heathrow Airport two years ago as the risk was "unrecognised at that time", an official accident report has said.
The crash of the British Airways 777 on 17 January 2008 came after the plane lost power due to a restricted fuel flow to both engines, according to the final report from the Air Accidents Investigation Branch (AAIB).
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.
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 an 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 10C (14F). 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. 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 was put out three seconds 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.
Nine safety recommendations were made following interim AAIB reports into the BA incident. Boeing and aero engine company Rolls-Royce took steps to prevent the ice phenomenon from re-occurring. In its final report, the AAIB has made nine further safety recommendations, including some which address plane crashworthiness.