The National Transportation Safety Board, the independent safety investigator of the United States, has issued two urgent safety recommendations (A-12-52 and A-12-53) on General Electric GEnx engines, which power the latest generation of Boeing aircraft; the 787 Dreamliners and the Boeing 747-8 both freighters and Intercontinental passenger jets.
The GEnx-1B engines power the 787 Dreamliners operating with Air India, Japan Airlines (JAL), Ethiopian Airlines, and soon, Qatar Airways. The two other 787 operators All Nippon Airways (ANA) and LAN Chile, have their aircraft powered by the Rolls Royce Trent 1000 engines.
The investigation of the GEnx engines began with the July 28th engine failure incident at Charleston, SC, USA, involving a Boeing 787 Dreamliner destined for Air India. Initial investigations suggested a fracture failure of the fan midshaft (FMS), first reported by Bangalore Aviation. While that investigation is still on-going, on August 31, the NTSB found similar indications on another GEnx-1B fitted on, a yet to fly, 787. The fan midshaft was removed from that engine for further inspection and examination. As a result of the investigative work to date, the NTSB has determined that the fan midshafts (FMS) on the GEnx engines fractured or cracked at the forward end of the shaft where the retaining nut is installed.
The NTSB is also concerned about a loss of power on the GEnx-2B engine of a Boeing 747-8F cargo flight, operated by Air Bridge Cargo, at Shanghai, China, during take-off. The airplane had accelerated through 50 knots when the engine’s low pressure rotor speed dropped. The pilot rejected the takeoff and returned to the ramp. Photographs of the low pressure turbine show damage similar to the GEnx-1B engine from the Charleston incident.
The urgent recommendations are: (1) (A-12-52) Issue an airworthiness directive to require, before further flight, the immediate ultrasonic inspection of the fan midshaft (FMS) in all GEnx-1B and -2B engines that have not undergone inspection, and (2) (A-12-53) Require repetitive inspections of the fan midshaft at a sufficiently short interval that would permit multiple inspections and detection of a crack before it could reach critical length and the fan midshaft fractures.
NTSB Chairman Deborah A.P. Hersman said
“The parties to our investigation — the FAA, GE and Boeing — have taken many important steps and additional efforts are in progress to ensure that the fleet is inspected properly,” “We are issuing this recommendation today because of the potential for multiple engine failures on a single aircraft and the urgent need for the FAA to act immediately.”
The engine manufacturer, GE, has developed a field ultrasonic inspection method to inspect the fan midshaft in the area where the fracture and crack occurred. This inspection can be done with the engine still installed on the airplane, thus saving operators a lot of money and downtime. To date, all in-service and spare GEnx-1B engines have been inspected. In addition, all GEnx-2B engines on passenger airplanes have been inspected. However, as per the the NTSB, approximately 43 GEnx-2B engines mounted on 747-8F cargo airplanes have not yet been inspected, and this is a concern on potential fan midshaft failures.
The NTSB is still continuing its investigations, but these safety recommendations have the potential of snow-balling in to a major issue for national carrier Air India. After the Charleston incident, delivery of the first 787 for the carrier was delayed, with Indian aviation regulator, the DGCA, slow to grant safety clearance. At least two possibly three 787s were due to be delivered in rapid succession in the next few weeks. Will the carrier delay induction awaiting clarifications from the engine manufacturer?
Prudence demands they should. After all, engines can make up more than 30% the cost of the aircraft, and need to be beyond 100% reliable.
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