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.

The risk was “unrecognised at that time”, a final report from the Air Accidents Investigation Branch (AAIB) said.

It added that the crash in January 2008 came after the British Airways plane lost power due to a restricted fuel flow to both engines.

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 which was carrying 136 passengers.

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” where 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 trapped water but did not identify the scenario of accumulated ice release and subsequent restriction to fuel flow.