GE expects the U.S. Federal Aviation Administration to issue an airworthiness directive (AD) detailing inspection intervals for GEnx engines “within a day or two,” following the latest contained failure of a GEnx-2B in Shanghai, China.
The company has decided to coat the fan midshaft on its GEnx turbofans with a formulation containing more lead after investigators determined corrosion caused the July 28 contained failure in the “back end” of a GEnx-1B installed on an Air India Boeing 787 as it performed ground tests in Charleston, South Carolina.
A GE spokesman told AIN that the company has adopted the coating process now used on the GE90-115Bs, abandoned for the GEnx in an effort to lessen environmental concerns associated with lead use. “The FAA is aligned with GE on the changes to the coatings,” he said, referring to the return to the older coating on the GEnx. He added that engineers would finish inspecting all GEnx engines in the field imminently.
The NTSB has recommended that the FAA issue an AD to address the failures—the most recent involving a GEnx-2B attached to an AirBridgeCargo 747-8 that lost power during a takeoff roll in Shanghai, China on September 11. That incident, which also apparently involved a fractured fan midshaft, followed the discovery on August 31 of a similar crack in the same area of the same part in a GEnx-1B installed on another Boeing 787 that hadn’t yet flown. The recommendation said the incidents appear “similar in nature.”
Investigators have found that the parts all developed fractures and/or cracks at the forward end of the shaft, rear of the threads where assembly calls for installation of a retaining nut. The GEnx engine uses a “dual shaft” design, meaning one shaft connects the compressor spool at one end to the high-pressure turbine spool at the other end. A longer “fan shaft” connects the fan and booster in the front of the engine to the low-pressure turbine in the back.
GE has developed a field ultrasonic method to inspect the suspect area while the engines remain on the airplanes. As of September 15, all in-service and spare GEnx-1B engines had undergone inspection, as did all GEnx-2B engines on passenger airplanes. However, at the time the NTSB said it knew of some 43 GEnx-2B engines on 747-8F cargo airplanes that still needed inspecting. On September 17 the GE spokesman told AIN that all GEnx engines in the field would have undergone inspection by the time the FAA issued its AD this week.