The most recent incident involved a Delta Airlines 777-200ER (N862DA) enroute from Shanghai to Atlanta on 26 November 2008 with 232 passengers and 15 crew. Pilots experienced an uncommanded rollback of the right Rolls-Royce engine while in cruise at 39,000ft approximately 40 minutes after a programmed step-climb. The crew was able to recover the engine after performing flight manual procedures related to the problem and descending to 31,000ft.
The common failure mechanism in the two incidents would appear to be water ice that accumulated at the front of a series of tubes that carry the fuel to the engine. Part of the fuel-oil heat exchanger, the tubes are located next to fluid lines carrying heated engine oil. From a design standpoint, the mutually beneficial system allows the engine oil to be cooled by the cold fuel while the fuel itself is heated for better combustion performance.
Under certain conditions however, Boeing engineers working in the laboratory have found that the heat generated by the Rolls-Royce designed fuel-oil heat exchanger is not adequate to prevent moisture in the fuel from freezing, a condition that tests have shown will produce ice the blocks the entrance of the fuel to the exchanger, starving the engines.
