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The previously unknown problem was revealed in a report into the accident on 17 January involving a British Airways flight from Shanghai. The Air Accidents Investigation Branch is urging European and US regulators to introduce interim measures for all Boeing 777s powered by Rolls-Royce Trent 800 engines to prevent a similar incident.

It also wants the aviation industry to ensure that fuel systems can cope with the potential build-up and sudden release of ice. The findings could result in long-haul flights being made to fly at lower altitudes to prevent the build-up of ice crystals inside their fuel tanks.

Flight BA038 was seconds away from touching down when it lost power. The pilot did not even have time to warn his 136 passengers to brace themselves before he realised the jet was not going to reach the runway.

In what was the most serious incident at Heathrow for 30 years, passengers were flung forward as the aircraft stalled 400 yards short of the south runway, skimmed a perimeter fence and careered to a halt on a grass verge. One person suffered a broken leg and eight others received minor injuries. It later emerged that the cockpit crew could not get the required thrust as the jet approached Heathrow.

AAIB experts now believe the formation of ice meant that fuel could not be delivered fast enough to the 777's Rolls-Royce Trent engines. They ruled out any problems with the quality of the fuel or mistakes by the crew.

The AAIB report – the fifth released so far – 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."

Although the Boeing's fuel did not freeze, its temperature fell to -34°C (-29°F) and stayed there for about 80 minutes. Investigators said the problems might have been caused by the length of time the fuel temperature was below zero, coupled with the sudden change in fuel flow demanded as it attempted to land.

The report added: "Although the exact mechanism in which the ice has caused the restriction is still unknown in detail, it has been proven that ice could cause a restriction in the fuel-feed system. The risk of recurrence needs to be addressed in the short term whilst the investigation continues."

The AAIB suggested the problem could be solved with the use of military technology which combats the formation of ice. It added: "Operational changes to reduce the risk of ice formation causing a restricted fuel flow at critical stages of flight could be introduced. Such changes could be implemented quickly, but must not compromise the safe operation of the aircraft."

The investigation into the crash is continuing with testing at Rolls-Royce in Derby, and at the home of Boeing in Seattle. BA said it was working closely with the investigation team.

Following the release of yesterday's report, a spokesman for the US Federal Aviation Administration said it would be issuing an airworthiness directive to all US carriers operating Boeing 777 aircraft.

This was likely to recommend "changes in procedures for pilots to follow in certain cold weather conditions", as well as "changes in certain fuel procedures on the ground". While it would not be an emergency directive, he added, it was likely to be issued within 24 hours and would have immediate effect.

Source: Michael Savage - The Independent