The US Federal Aviation Administration has limited extended operations for Boeing 787s with Rolls-Royce Trent 1000 engines.
The airworthiness directive (AD) published on the United States’ Federal Registry on Monday (US time) said affected aircraft would be allowed to fly no further than 140 minutes from an alternate airport.
Previously, the US FAA had allowed 330-minute ETOPS approval for the 787, which meant the aircraft could be flown on a route that kept it within five and a half hours flying time on a single engine from an alternate airport in the event of an engine failure.
“This AD was prompted by a report from the engine manufacturer indicating that after an engine failure, prolonged operation at high thrust settings on the remaining engine during an ETOPS diversion may result in failure of the remaining engine before the diversion can be safely completed,” the FAA’s AD said.
“We are issuing this AD to address the unsafe condition on these products.”
Rolls-Royce Trent 1000 ‘Package C’ engines, of which about 380 are in service powering Boeing 787-9s, including with Air New Zealand, All Nippon Airways and British Airways, have been experiencing earlier than expected turbine blade wear.
Airlines have already been forced to park aircraft while waiting for their Trent 1000 Package C engines to be inspected, repaired and/or replaced amid a shortage of replacement engines.
The US FAA AD said: “Boeing reported to the FAA that the engine manufacturer recently determined that intermediate pressure compressor (IPC) stage 2 blades have a resonant frequency that is excited by the airflow conditions existing in the engine during operation at high thrust settings under certain temperature and altitude conditions.”
“The resultant 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, thrust on the remaining engine is normally increased to maximum continuous thrust (MCT).
“During a diversion following a single engine shutdown under an ETOPS flight, the remaining engine may operate at MCT for a prolonged period, under which the IPC stage 2 blades would be exposed 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.
“In addition, if the remaining engine already had cracked IPC stage 2 blades, the likelihood of the remaining engine failing will further increase before a diversion can be safely completed.”
The US FAA’s ruling followed the European Aviation Safety Agency (EASA) calling for more regular checks on the intermediate pressure compressor rotor blades.
“This condition, if not detected and corrected, could lead to inflight blade release, possibly resulting in reduced control of the aeroplane,” the EASA AD published on April 13 said.