THE crash landing of a British Airways Boeing 777 at Heathrow may have been caused by abnormally cold conditions over Russia, air investigators said yesterday.
Flight BA38 was forced to make an emergency landing at Heathrow when it lost thrust in both engines at 600ft coming in to land on January 17.
Witnesses described seeing the airline bank sharply to the left and miss the tops of houses by 200ft as First Officer John Coward glided the aircraft to safety.
It missed the perimeter fence by inches before touching down on the grass, leaving one passenger seriously injured and 12 others slightly hurt.
Yesterday, in an interim report, the Air Accident Investigations Branch (AAIB) said the drop in temperatures to -105F (-76C) may have caused the fuel in the aircraft to thicken during the flight which meant it was unable to get the additional thrust needed to land.
Further tests will be carried out to establish precisely what happened.
The circumstances leading to the worst aviation accident at Heathrow in more than 30 years will raise some concerns over the safety of the Boeing 777. However, neither Britain's safety regulators, Boeing, nor Rolls Royce, the engine's manufacturers, have recommended operational changes.
There are 667 Boeing 777s in service - with 40 in the British Airways fleet - and it is regarded as one of the safest airliners in the world. None has been lost since the plane first flew in 1995.
In its report the AAIB has focused on the "region of particularly cold air'' between the Urals and Eastern Scandinavia during the 10-hour flight from Beijing to Heathrow.
It found that temperatures plummeted far lower than would have been expected for the region.
As a result, AAIB experts are examining what this would have done to the fuel and whether this would have caused a change in its consistency. Although the weather was unusually cold, it was not
unprecedented and such problems have never been reported before.
The AAIB has established that the fuel used on the aircraft was of high quality.
While the average freezing temperature of aviation fuel is -53F (-47C), tests showed that the fuel used on the airliner does not turn to ice until -71F (-57C). Tests also found that the fuel temperature throughout the flight never dropped below -29F (-34C).
Even though the fuel did not become frozen it could have thickened to an unusual extent, which could have restricted its flow. Fresh tests on fuel are being carried out both at Rolls-Royce's engine plant in Derby and Boeing's factory in Seattle.
A number of other theories have been ruled out by the AAIB. They include birds flying into the engine or ice blocking the engine intake.
David Learmount, the operations and safety editor at Flight International, said all the evidence was starting to point towards the consistency of the fuel. "There might have been an issue with viscosity - with the fuel becoming thicker and flowing less well,'' he said.
