London - The crash landing of a British Airways Boeing 777 in London in January was probably caused by ice blocking its fuel system, a report by Britain's Air Accidents Investigation Branch (AAIB) said Thursday.

Investigators believe that a restriction in the fuel flow caused the plane's engines to lose power less than a minute before touchdown at London's Heathrow airport on January 17.

But they said they are still "uncertain" as to how the ice could have formed.

The AAIB called on airlines to introduce measures to cut the risk of ice causing fuel blockages.

The pilots of the Boeing 777 managed to land the plane safely, and 136 passengers and 16 crew escaped without serious injury.

The report said the plane flew through unusually cold air over Siberia en route from Beijing to London's Heathrow airport. However, the temperatures were "not unique," it added.

"The investigation has shown that the fuel flow to both engines was restricted - most probably due to ice within the fuel feed system," said the report.

"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."

Aircraft are designed to cope with significant amounts of the ice crystals which form in fuel when they climb into sub-zero atmospheric conditions.

"The accident flight was unique in that this has been the only recorded case of a restricted fuel flow affecting the engine performance to the extent of causing HP pump cavitation" - the damage found within the pumps that alerted the investigators to the loss of fuel pressure, said the report.

"This is the first such event in 6.5 million flight hours and places the probability of the failure as being 'remote'," it added.

The report recommended that the US Federal Aviation Administration and the European Aviation Safety Agency introduce interim measures to reduce the risk of ice forming on the Boeing 777, powered by Trent 800 engines, and should consider the implications for other aircraft types. (dpa)