An NTSB photo showing the accumulation of ice on the FOHE during tests.

Following two air safety ‘engine thrust rollback’ incidents in 2008, the US National Transportation Safety Board (NTSB) and the UK Air Accident Investigation Branch (AAIB) have recommended that Rolls-Royce, manufacturer of Boeing 777s, redesigns its fuel/oil heat exchanger (FOHE) engine component. 

The rollbacks were caused by a build-up of ice on the FOHE, which restricted the flow of fuel to the engine, on Boeing 777-200ER airplanes powered by Rolls-Royce RB211 Trent 800 Series engines. This caused two incidents, one in the UK and one in the US.

On 17 January 2008, a Boeing 777 crashed short of London’s Heathrow airport runway, resulting in substantial damage and 13 injured. A Delta Airlines Boeing 777 also experienced an engine rollback while en route from Shanghai to Atlanta on 26 November 2008.

In response to AAIB’s initial findings, Boeing developed procedures to help prevent engine ice accumulation. Rolls-Royce has also indicated that a redesign of the FOHE is in progress and would be ready for installation in 12 months. Procedures have been given to reduce the risk of incident, however the NTSB believes these may “add complexity to flight crew operations”, and so has called for a complete re-design.

Mark V. Rosenker, Acting Chairman of NTSB, said: “With two of these rollback events occurring within a year, we believe that there is a high probability of something similar happening again. We are encouraged to see that Rolls-Royce is already working on a redesign, and we are confident that with the FAA and EASA (European Aviation Safety Agency) overseeing the process, this flight safety issue – even one as complex as this – will be successfully and expeditiously resolved.”

In response to the recommendation for an engine redesign, Boeing and Rolls-Royce said: “Boeing and Rolls-Royce have accepted the above recommendation. To mitigate the potential for a future fuel system ice accumulation and release event, to cause a blockage at the inlet to the FOHE, Rolls-Royce have developed a modification to the FOHE. The modification will improve the FOHE’s capability in the event of a fuel system ice release event.”

Click here to read AAIB’s interim report into the January 2008 incident at Heathrow.