General Electric (GE) has completed an analysis of ultrasound inspections on all six Boeing 787s powered by an engine that failed in ground taxi tests six weeks ago.

The results of the ultrasounds have not been disclosed publicly, but all six GEnx-powered 787s delivered to three airlines are still operating, the manufacturer says.

GE has forwarded the data from the ultrasound checks on the GEnx-1B fleet to the National Transportation Safety Board (NTSB), which is still investigating the root cause of the incident in North Charleston, South Carolina. on 28 July.

Ultrasound inspections on 92 GEnx-2Bs, the powerplant for 26 delivered Boeing 747-8s, remain ongoing, GE says.

GE ordered the inspections after the NTSB traced the GEnx-1B engine failure on 28 July to cracks in the fan mid shaft assembly. The cracks caused the assembly to break up, which forced the first stage of the low-pressure turbine to collide with trailing stages.

The fragments from the stages were ejected out of the engine nozzle as designed, avoiding the more serious problem of parts escaping the fan case that shields the passenger cabin of the aircraft from such debris.

But the incident put a spotlight on the integrity of the fan mid shaft design, which is supplied by Japan's IHI. Such failures are extremely rare. GE has recording only a handful of cracking incidents on fan mid shaft assemblies over several decades of service on the manufacturer's other commercial engines, which include the CF6 powerplant for widebodies such as the Boeing 767 and Airbus A330.

It is still not clear what caused the cracks to develop inside the fan mid shaft assembly. In rare previous failures on the CF6, GE discovered that they were caused by contaminants, oil leaks and other components wearing unexpectedly against the fan mid shaft.

"The voluntary inspection to the -1B and the -2B fleets provide GE Aviation with additional engineering data to use in the investigation with the NTSB, Boeing and IHI to determine the cause of the fan shaft fracture," GE says.

Source: Air Transport Intelligence news