Boeing and General Electric said Wednesday they told airlines to inspect and possibly replace the engines on some Boeing 777 jets because of a potential manufacturing defect in a gearbox.

The engine-maker issued two service bulletins to airline operators after two in-flight engine shutdowns this year traced to a defect in gearboxes from a batch produced between September and March.

The 777 is a long-distance aircraft with just two engines. GE said airlines should urgently check 25 in-service 777s that have suspect gearboxes on both engines.

GE is still pinning down the exact number of other airplanes affected but said that a total of about 118 gearboxes are in the batch with the suspected defect

    Most Read Stories

If one engine fails, the 777 can continue on the other engine, but the plane must divert to the nearest airport.

On Feb. 11, a Aeroflot 777-300ER delivered just 10 days earlier was approaching Moscow on a flight from Bangkok when an engine shut down. The plane landed safely.

Then last Thursday, an Air China 777-300ER en route from Beijing to Paris diverted to Stockholm after an engine failure.

GE spokesman Rick Kennedy said the engine maker found that in both cases a small gearbox under the front fan that pumps oil and fuel around the engine was found to have cracked and separated.

He said a defect in the advanced metal alloy is suspected. The gearbox is made by Avio of Italy.

“GE is continuing to investigate the root cause,” Kennedy said. “No formal conclusions have been reached.”

He added that more than 1,150 of these engines are in service and that the gearbox has operated with the engines for almost 15 years with extremely high reliability over 40 million flight hours.

In 2008, according to a report by aviation trade publication FlightGlobal, the same gearbox ”broke out if its housing” on an Air France 777, causing an engine shutdown and diversion.

“We’ve had one or two issues in 15 years,” Kennedy said. “They are very reliable overall.”

Avio and GE have developed an electromagnetic testing process to inspect the metal for interior defects on all new engines produced now.

Kennedy said inspection and any necessary modification work on the 25 planes that may have two suspect engines will be completed by the end of the week.

“GE is working closely with both Boeing and the Federal Aviation Administration on this aggressive fleet action,” Kennedy said.

American Airlines, the only U.S. carrier affected, has six 777-300ERs in its fleet, but only four have gearboxes from the period covered in the bulletins.

Airline spokeswoman Andrea Huguely said the recommended changes to those four jets will be completed before Monday “with no expected impact to our customers.”

In addition to the in-service 777s, Boeing has 14 undelivered production 777s with gearboxes that must be inspected and potentially replaced, said company spokesman Marc Birtel.

GE’s figures indicate there are roughly 40 airplanes in service that have a gearbox from the suspect batch on just one engine.

The gearbox issue was first reported by The Wall Street Journal’s website.

Dominic Gates: (206) 464-2963 or dgates@seattletimes.com