The U.S. Federal Aviation Administration (FAA) (Washington, DC, USA) recently issued an airworthiness directive placing more stringent limitations on the flight of select Boeing 787-8 and 787-9 airplanes due to concerns over turbine corrosion. In its directive, the FAA cites numerous reports of engine inspection findings of cracked blades resulting in unscheduled engine removals.
The FAA notice, which applies to aircraft with several Trent 1000 turbofan engines, requires revising the flight manual to limit extended operations from these airplanes. The directive calls for aircraft with these engines to always remain within 140 minutes of a suitable airport, in case an early landing is necessary. The prior range for Boeing 787 aircraft was 330 minutes.
“Boeing reported to the FAA that the engine manufacturer recently determined that intermediate pressure compressor stage two 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 FAA writes in its directive. “The resultant blade vibration can result in cumulative fatigue damage that can cause blade failure and consequent engine shutdown.”
According to the FAA, thrust loss on one engine can also increase the likelihood of the remaining engine failing—and unrecoverable thrust loss on both engines could lead to a forced landing.
The agency says it issued the directive after evaluating all the information and determining that the unsafe condition is also likely to exist or develop in other products of the same design.
According to the FAA, the manufacturer is currently developing a modification designed to address the unsafe conditions. For more information, the full directive can be read here.
Source: FAA, www.faa.gov.