General Electric has warned airlines that 118 turbofan engines that power the Boeing 777-300ER may have a defective component and some need to be replaced immediately.
The two service bulletins issued by GE on 14 May likely precede an airworthiness directive from the US Federal Aviation Administration (FAA).
The actions by GE and the FAA come after two incidents in February and on 9 May involving the gear separation of the transfer gearbox, which led to in-flight engine-shutdowns by the GE90-115B, the massive turbofan that generates 115,000lb-thrust (510kN).
GE says it discovered that "material anomalies" may exist in a batch of engines manufactured from September 2012 to March 2013. What caused the anomalies is still under investigation, the company says.
GE also is working on an enhanced eddy current inspection process that will determine how many of the 118 engines actually have the material anomaly.
In the meantime, the company is focusing on the subset of aircraft flying with two engines manufactured during the six-month period where the anomalies may be present.
GE has identified 26 777-300ERs that are flying with a pair of the suspect engines. The other 66 engines are spares, undelivered or flying on aircraft with only one suspect engine.
For each of the 26 aircraft flying with a pair of suspect engines, GE says airlines must replace the transfer gearbox or one of the two engines immediately. The aircraft is still at risk of an in-flight shutdown due to transfer gearbox failure, but the 777-300ER can fly for several hours using only one engine. So far, two of 26 aircraft have already completed the replacement process and are cleared to resume flying.
Once the enhanced eddy current inspection test is available, GE will check for anomalies on all of the 118 engines.
The transfer gearbox delivers power from the engine to the accessory gearbox that drives the fuel and hydraulic pumps that the engine needs to operate. If the transfer gearbox fails, the engine shuts down immediately.
The GE90-115 has reported gearbox issues in the past, but the new material problem is not related to those issues, GE says.