By Karen Walker | August 8, 2012

A fan shaft fracture was the cause of a contained engine failure on a Boeing 787 during a pre-delivery taxi test, the US NTSB has determined.

The incident happened July 28 at Charleston Airport, S.C. (ATW Daily News, July 30). The GE Aviation GEnx engine was removed and taken to a GE facility in Cincinnati, OH, where it was disassembled for an investigation led by NTSB investigator-in-charge David Henson.

In a statement issued Wednesday, NTSB said, "As a result of the investigative work to date, the NTSB has determined that a fan mid-shaft on the failed GEnx engine fractured at the forward end of the shaft, rear of the threads where the retaining nut is installed.

The fan mid-shaft is undergoing several detailed examinations including dimensional and metallurgical inspections."

Having determined what caused the contained failure, the investigation is now focused on what led to the fracture.The GEnx is a dual shaft engine, meaning that one shaft connects the compressor spool at one end to the high pressure turbine spool at the other end. The fan shaft connects the fan and booster in the front of the engine to the low pressure turbine in the back.

Investigators will continue the detailed examination of the engine and metallurgical analysis of its components and have also begun reviewing the engine manufacturing and assembly records, NTSB said.

According to GE, this type of fracture is not unknown, but is extremely rare. In 10 years, there have been only six instances across all operating engines and 600 million flight hours.

FAA, Boeing and GE experts are all assisting the investigation. So far, there seems to be no safety implications for the installed fleet.