Airlines were urged yesterday to implement safety measures to reduce the risk of ice restricting fuel flow, after the crash of a British Airways jet at Heathrow earlier this year.

A report, the fifth to be released by the Air Accidents Investigation Branch (AAIB) into the incident, concluded that the crash, on January 17, was probably caused by ice within the fuel-feed system.

Now the AAIB wants aviation regulators to introduce interim measures for all Boeing 777s powered by Rolls-Royce Trent 800 engines to prevent a similar incident. It also wants watchdogs to consider the implications of the findings for other types of aircraft and to ensure that fuel systems can cope with the potential build-up and sudden release of ice.

The crash was the most serious in the 12-year history of the Boeing 777 and the most serious incident at Heathrow for 30 years. Passengers were flung forward when the BA flight from Beijing skimmed the perimeter fence and shuddered to a halt 400 yards from where it first touched down, and in less than half its normal minimum landing distance when using full braking power. One person suffered a broken leg and eight others received minor injuries.

BAA, the airport operator, closed the runway and diverted dozens of flights, including the Prime Minister’s chartered British Airways 747, which was left stranded at its departure gate.

It later emerged that the crew on the Beijing flight were unable to get the required thrust from the engines as the jet made its approach. John Coward, 41, the co-pilot, took control for the landing. By 200ft the airspeed had reduced to about 108 knots and the autopilot disconnected at 175ft.

Yesterday the AAIB 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 investigators said that they had ruled out problems with fuel quality or quantity or mistakes by the flight crew, they found abnormal marks on the high-pressure fuel pumps from the engines. They said that these were formed by a phenomenon called “cavitation”, which is caused by a restriction in the fuel flow to the pump.

Aircraft are designed to cope with significant amounts of the ice crystals that form in fuel when they climb into sub-zero temperature zones. However, tests on a Trent 800 engine of the type fitted to the BA jet showed that restricting fuel flow to the high-pressure pump caused a similar effect to that recorded in the accident.

Investigators noted that the BA aircraft encountered very low temperatures en route from China, but comparison with flights on other routes showed that they were not unique.

However, the flight was exceptional for the length of time the fuel in the main tanks had stayed below 0C, as well as for the low fuel-flow demands while cruising and the high fuel-flow demands in the final approach to the Heathrow runway.

A spokesman for BA said: “There are no safety recommendations specific to British Airways. We will work closely with the relevant regulatory authorities and comply with any requirements issued to all operators [of the aircraft]”.

The AAIB’s final report into the BA crash landing will be published at a later date.

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