Updated on April 17 to reflect publication of final rule
The U.S. Federal Aviation Administration (FAA) published an Airworthiness Directive on April 17 calling for a reduction of ETOPS (extended twin engine operations) limits from 330 to 140 minutes for Boeing 787-8s and 787-9s powered by certain Rolls-Royce Trent 1000 turbofans. The order follows reports from Rolls that prolonged operation at high thrust settings might result in an engine failure before completion of a diversion to an alternate airport. The posting, originally appearing on the Federal Register’s public inspection page on April 16, covers Package C engines, which have suffered several failures over the past year due to premature wear in their intermediate-pressure compressor and turbine blades and seals.
Boeing reported to the FAA that Rolls-Royce recently determined that airflow conditions existing in the engine during operation at high thrust settings under certain temperature and altitude conditions excite resonant frequency in the intermediate pressure compressor (IPC) stage 2 blades. The resulting blade vibration can result in cumulative fatigue damage that can cause blade failure and consequent engine shutdown. In the event of a single engine in-flight shutdown during the cruise phase of flight, flight crew normally increase power to maximum continuous thrust on the remaining engine. During a diversion following a single engine shutdown under an ETOPS flight, the remaining engine might operate at MCT for a prolonged period, exposing the IPC stage 2 blades to the resonant frequency condition. Therefore, an ETOPS diversion will put the remaining engine at an operating condition that would significantly increase the likelihood of failure of the remaining engine, said the FAA. Furthermore, it added, if the remaining engine already had cracked IPC stage 2 blades, the likelihood of the remaining engine failing would increase during a diversion.
The FAA estimates that the ruling will affect 14 airplanes under U.S. registry. Rolls-Royce reports that, globally, 380 Package C engines operate in service, while Boeing estimates that they power some 25 percent of all 787s in operation.
The FAA’s planned publication of the order follows an April 16 AD from the European Aviation Safety Agency (EASA) that calls for more frequent inspections of Package C Trent 1000s. That order came three days after Rolls-Royce reported that it had advised operators of the need for further inspections.