Both engines of the British Airways jet that crash-landed at Heathrow were still running when it came down.

The Air Accident Investigation Branch (AAIB) has issued updated findings indicating its inquiry may now focus on the aircraft's fuel supply system.

Various theories about what caused the jet to lose power have been put forward, including the possibility of fuel contamination.

In the update, the AAIB repeated that the Boeing's twin Rolls-Royce engines failed to respond to demands for more thrust as it came in to land.

It said: "The engines both initially responded but after about three seconds the thrust of the right engine reduced.

"Some eight seconds later the thrust reduced on the left engine to a similar level.

"The engines did not shut down and both engines continued to produce thrust at an engine speed above flight idle, but less than the commanded thrust."

The AAIB said it was carrying out a "detailed analysis and examination of the complete fuel flow path from the aircraft tanks to the engine fuel nozzles".

Recorded data shows the aircraft had enough fuel and its autothrottle and engine control systems had worked as expected, the AAIB said.

The AAIB intends to publish a preliminary report within 30 days of the incident.

Disaster was narrowly avoided when the Boeing 777, carrying 136 passengers and 16 crew, lost power in mid-air as it approached the airport on January 17.

It has emerged American investigators have recorded six previous engine failures involving the same type of aircraft.

The most recent was in September 2006, when a Malaysia Airlines Boeing 777's right engine shut down near Brisbane, Australia.

The US National Transportation Safety Board's website lists another five incidents, including one in August 2005 where a 777 lost thrust after taking off from Perth, Australia.

A British aviation industry source stressed seven engine failures was "not a large figure" given the aircraft's long flight history and questioned how similar the previous incidents were to the BA crash-landing.

The Boeing 777 is certified by the US Federal Aviation Administration (FAA) and its Rolls-Royce engines are certified by the European Aviation Safety Agency (EASA).

A spokesman for the Civil Aviation Authority said: "We regulate BA as an airline, so we need to be content they are meeting all regulations and requirements.

"As far as any modifications or inspections are concerned, that would come from the AAIB recommending it and the FAA or EASA making it a legal requirement after consulting with the manufacturer."

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