Sept. 4 (Bloomberg) -- Boeing Co. 777 pilots will be told to rev up their engines before landing to clear ice from fuel lines after frozen kerosene was found to have caused the crash- landing of a British Airways Plc jet in January.

Pilots of 777s also should change altitude periodically when flying through very cold air, Boeing spokesman Nick West said today after U.K. crash investigators recommended that the Chicago-based company take steps to reduce the risk of icing.

The British Airways plane with 152 passengers and crew crash-landed on Jan. 17 after the engines couldn't provide enough thrust while approaching London Heathrow airport. The 777 flew from Beijing through temperatures of minus 73 degrees Celsius, possibly thickening the fuel and reducing its flow, the Air Accidents Investigation Branch said in a statement today.

``Although the exact mechanism in which the ice has caused the restriction is still unknown, it has been proven that ice could cause a restriction in the fuel-feed system,'' the board said. ``The risk of recurrence needs to be addressed in the short term while the investigation continues.''

Boeing and Rolls-Royce Group Plc, which made the engines on the British Airways jet, should work with the U.S. Federal Aviation Administration and European Aviation Safety Agency to introduce interim measures for the 777, the U.K. board said.

Full Throttle

Boeing's West said the initial instructions will be to periodically vary altitude when fuel in the main tank is below minus 10 degrees Celsius, and to advance the throttle to maximum for 10 seconds before the final descent when fuel has been below that temperature for more than three hours, clearing out any water buildup.

The instructions cover 220 777s powered by Rolls-Royce Trent 800 engines in service with 11 airlines worldwide, Boeing said. For 777 aircraft on the ground in freezing conditions, fuel pumps must be run at maximum for one minute each to prevent water buildup, the planemaker said.

In the U.S., the FAA will send a directive within two days covering 56 777s operated by AMR Corp.'s American Airlines and Delta Air Lines Inc., agency spokeswoman Alison Duquette said. The carriers will have 10 days to comply, she said.

While the findings of the London crash probe were based on planes with Rolls-Royce engines, the FAA and European safety agency should take steps to check whether 777s with other powerplants might also be affected, the U.K. board said.

U.S. Safety Board

A design change would make the fuel system more ``resilient,'' the U.S. National Transportation Safety Board said in a statement. Still, such a move would take time, so interim measures are needed, the NTSB said.

The British Airways crash-landing ripped off wheels and cracked one wing. No one was seriously injured and there were no fatalities.

Even with particularly cold air over Russia, the fuel in that jet never reached a temperature lower than minus 34 degrees Celsius, compared with a freezing point for kerosene of at least minus 47 degrees, suggesting the ice was formed from water that exists naturally in fuel, the U.K. safety board said.

Research into previous 777 operations showed that of 141,000 flights, 0.2 percent experienced fuel temperatures as low as the British Airways plane. Of 13,000 flights with Rolls- Royce engines, 118 had temperatures matching the minus 2 degrees experienced in Beijing, and only 70 the minus 22 degrees measured on the plane's final approach to Heathrow.

The chances of such an accident happening were ``remote,'' the AAIB said.

Boeing's 777 model is regarded as one of the safest in the industry, with just six other accidents reported in its 13-year flying history. The manufacturer has built 713 of the type.

To contact the reporters on this story: Sabine Pirone in London at spirone@bloomberg.net; Steve Rothwell in London at srothwell@bloomberg.net.

Last Updated: September 4, 2008 14:43 EDT