LONDON, Feb 9 (AFP) - A build-up of ice in the fuel system caused a British Airways plane to crash-land at London Heathrow in 2008, investigators said Tuesday, adding that safety checks would not have identified the problem.

The Boeing 777 from China crashed short of the runway on January 17, 2008, after losing power due to a restricted fuel flow to both engines, according to the final report from the Air Accidents Investigation Branch (AAIB).

All 136 passengers and 16 crew on board escaped safely, although with a few minor injuries.

The AAIB said the problem was probably caused by a build-up of ice within the fuel system, formed from water that occurred naturally in the fuel when the plane operated with low fuel flows over a long period and it got very cold.

Investigators said that plane safety requirements at the time would not have identified the problem.

"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 AAIB's report said.

It said that research in the 1950s had identified the problem of ice in the fuel systems but did not identify the scenario of accumulated ice release and subsequent restriction to fuel flow.

There were no published guidelines or tests to check whether a fuel system was susceptible to ice, the AAIB said.

In the Heathrow crash, a part of the engine called the fuel oil heat exchanger was found to be susceptible to fuel restrictions when presented with soft ice in a high concentration and very low fuel temperatures.

Nine safety recommendations were made following earlier AAIB reports into the BA incident, and Boeing and aero engine company Rolls-Royce took steps to prevent the ice phenomenon from re-occurring.

In their final report Tuesday, the AAIB made nine further safety recommendations, including some which address the ability of an aircraft to withstand an accident.