Following two engine thrust rollback events on Boeing 777 aircraft powered by Rolls-Royce engines, the National Transportation Safety Board (NTSB) has issued an urgent safety recommendation calling for the redesign of a Rolls- Royce engine component. 

The Safety Board also recommended that, after the redesign is completed, the new system be installed on all affected B-777 airplanes at the next maintenance check or within six months.

The recommendations were issued in response to the findings in two investigations involving engine thrust rollbacks on Boeing 777-200ER airplanes powered by Rolls-Royce RB211 Trent 800 Series engines.  In both cases a build-up 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 an uncommanded engine rollback.

The first event occurred on January 17, 2008 when a B-777 experienced a dual engine rollback on final approach and crashed short of the runway at London's Heathrow International Airport.  The second event occurred on November 26, 2008, when a Delta Air Lines B-777 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.  As more information from the Delta rollback event was developed, Boeing modified the procedures, which became the basis of an airworthiness directive issued by the FAA.

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.

Because of these hazards, the Safety Board has determined that the only acceptable solution to this safety vulnerability is a redesigned FOHE that would eliminate the potential of ice build-up. On February 23, 2009, 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.