Prompted by the 2008 crash landing of a British Airways Boeing 777 at London Heathrow, the Federal Aviation Administration (FAA) is proposing modifications that would prevent ice accumulation inside the fuel systems of certain B-777/engine combinations.

The move, requiring installation of redesigned oil cooler systems on B-777s powered by Rolls-Royce RB211Trent 800 powerplants, must be completed by January 2011 and follows the lead of the European Aviation Safety Agency (EASA) There are about 220 Rolls-Royce-powered B-777s, of which 50 operate in the United States and are therefore affected by the FAA's proposal. American Airlines has the largest B-777 fleet with the British-made engines operating in the U.S.

On January 17 2008, British Airways Flight 38 slammed into the ground at London Heathrow just short of the runway when both of the plane's engines lost substantial thrust. All passengers survived the incident. It was later determined that ice formed during the China-UK flight over the polar region (during unusually cold outside temperatures) had plugged up the aircraft's fuel system.

In March, following two engine thrust rollbacks involving Trent 800-powered B-777s, the U.S. National Transportation Safety Board issued urgent recommendations to redesign the oil-cooler system on Rolls-Royce Trent 800 engines.

The urgent safety recommendation called for redesign of an engine component---work that was already underway at Rolls-Royce. The Safety Board also recommends that the redesigned unit be installed on all affected B-777s at the next maintenance check or within six months of availability.

In both cases, a buildup of ice (from water normally present in all jet fuel) on the fuel/oil heat exchanger (FOHE) restricted the flow of fuel to the engine, resulting in uncommanded engine rollbacks.

The second event occurred on November 26, 2008, when a Delta Air Lines B-777 (N862DA) experienced a single engine rollback during cruise flight over Montana while en route from Shanghai to Atlanta.

Testing in support of the UK accident investigation led Boeing to develop procedures to help prevent ice accumulation, and to recover thrust in cases of ice blockage.

The NTSB said that while the procedures may reduce the risk of a rollback in one or both engines due to FOHE ice blockage, they add complexity to flight crew operations, and the level of risk reduction is not well established. And because the recovery procedure requires a descent, the aircraft may be exposed to other risks such as rising terrain or hazardous weather, or the inability to achieve maximum thrust during a critical phase of flight, such as during a missed approach.

The only acceptable solution to this safety problem, the NTSB said, is a redesigned FOHE that would eliminate the potential of ice buildup. In February, Rolls-Royce indicated that a redesign of the FOHE was underway, and that they anticipated the redesign to be tested, certified and ready for installation within 12 months.

"With two of these rollback events occurring within a year, we believe that there is a high probability of something similar happening again," said the NTSB's Mark V. Rosenker, in calling for the system redesign.