An unusual rash of engine shutdowns since early December has temporarily stranded three normally reliable General Electric-powered Boeing 777-300ERs.

Although each incident involved a shutdown of the GE90-115B, GE's investigation so far indicates the causes of the power loss appears to have three different sources, says the engine manufacturer.

The incidents have forced two Air France twinjets to make emergency landings at alternate airports since 12 December. And on 1 February, a Singapore Airlines 777-300ER was forced to land at Frankfurt International Airport in Germany.

In the first incident, the Air France pilot crew noticed "excess vibrations" and powered down the engine, making an emergency landing in Rome. A visual inspection revealed excessive wear on a stage six low-pressure turbine blade that "reduced contact pressure between blades on that disk," says GE.

On 25 January, a second Air France 777 diverted to Milan Malpensa airport after an in-flight engine shutdown. The engine's transfer gearbox broke out of its housing, causing the power loss.

Finally, the SIA flight was disrupted by an undisclosed problem with the engine's accessories gearbox, resulting in the Frankfurt diversion. At the moment, GE is not certain whether the pilot commanded the engine to power down, or the engine failed in flight. GE continues to investigate the incident to discover the root cause of the gearbox problem.

Both the transfer gearbox and the accessories gearbox are produced by the same supplier, Italy's Avio. GE says it is "working with them to find out what the cause would be".

Both components have been installed on older-model aircraft equipped with GE90-94B engines, achieving an 11-year in-service record with no previous incidents before 25 January.

Air France was the launch operator for the GE90-115B-powered 777-300ERs, receiving its first aircraft in May 2004, so has the fleet's oldest airframes and engines in service.

Source: Flight International