Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for Rolls-Royce plc RB211-Trent 800 series turbofan engines. That AD currently requires replacing the fuel-to-oil heat exchanger (FOHE). This proposed AD would require replacing the FOHE on the RB211-Trent 500 and RB211-Trent 700 series turbofan engines in addition to the RB211-Trent 800 series turbofan engines. This proposed AD results from mandatory continuing airworthiness information (MCAI) issued by an aviation authority of another country to identify and correct an unsafe condition on an aviation product, and results from the risk of engine FOHE blockage. The MCAI describes the unsafe condition as:
In January 2008, a Boeing 777 powered by RB211-Trent 800 engines crashed short of the runway as a result of dual loss of engine response during the final stages of approach. The investigation of the incident has established that, under certain ambient conditions, ice can accumulate on the walls of thefuel pipes within the aircraft fuel system, which can then be released downstream when fuel flow demand is increased. This released ice can then collect on the FOHE front face and limit fuel flow through the FOHE. This type of icing event was previously unknown and creates ice concentrations into the fuel system beyond those specified in the certification requirements. In May 2009, an Engine Indicating and Crew Alerting System (EICAS) surge message was set following a successful go-around maneuver on a single RB211-Trent 700 engine of an A330 aircraft. Subsequent analysis concluded the likely cause to be temporary ice accumulation causing fuel flow restriction in the FOHE. The incident has indicated the potential susceptibility to ice blockage for Airbus aircraft in combination with Rolls-Royce engines that feature similar fuel systems to the RB211-Trent 800.
We are proposing this AD to prevent ice from blocking the FOHE, which could result in an unacceptable engine power lossand loss of control of the airplane.