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Thursday, August 9, 2012 - Page updated at 06:00 p.m.

NTSB says fan-shaft fracture caused 787 engine failure

By Dominic Gates
Seattle Times aerospace reporter

The National Transportation Safety Board (NTSB) said Wednesday its initial investigation of last month's 787 Dreamliner engine failure on the runway in North Charleston, S.C., has determined that the fan shaft fractured inside the GE-built engine.

The failure sparked a grass fire when hot debris was ejected from the back of the engine.

General Electric (GE) spokesman Rick Kennedy said a crack developed in the shaft that runs from the fan at the front of the engine through the core to the turbine at the back.

The fracture caused the rear part of the engine to slip backward slightly so that rotating blades in the turbine at the back of the engine hit static vanes connected to the engine case and broke into pieces.

Investigators are continuing the detailed examination of the engine and metallurgical analysis of its components and have begun reviewing the engine manufacturing and assembly records.

The shaft comes in two pieces connected by a nut: a forward piece holding the fan, and behind that a second piece holding the compressor and turbines. The crack occurred in the second part of the shaft, close to the nut that connects it to the forward part.

No conclusions have yet been drawn as to what caused the fan shaft to crack.

The incident, referred to as a "contained" engine failure because no debris penetrated the sides of the engine pod, occurred July 28 during a pre-delivery taxi test of an Air India 787.

No one was hurt, but the airport was forced to shut down for more than an hour while a crew swept the runway.

Kennedy said the breakup of the turbine at the rear of the engine is what is supposed to happen when a shaft cracks or breaks.

When the rear part of the shaft slips backward a very small distance and brings the rotating blades of the turbine into contact with the stationary vanes behind them, this immediately brakes the rotation speed of the shaft.

As the blades and vanes break up and spew out the back, the energy of the failure is greatly reduced.

"It prevents an uncontained failure," said Kennedy.

GE engineers must design any airplane engine to avoid the nightmare scenario of an uncontained failure midflight — pieces of metal flying out with so much energy that they pierce the engine pod and penetrate the wing fuel tanks.

Kennedy said fan-shaft fractures are "exceedingly rare."

He said GE has some 25,000 commercial-jet engines in service today and there have been just six shaft fractures in the past decade, about one every 100 million flight hours.

The GEnx engine shaft is supplied by Ishikawajima-Harima Heavy Industries (IHI) of Japan. GE assembles the engine at its facility in Peebles, near Cincinnati, Ohio.

This engine is one of two offered on the 787, with the alternative Trent 1000 engine built by Rolls-Royce. Another version of the GEnx engine is used to power the new 747-8 jumbo jet, 21 of which are in service.

So far, Boeing has delivered only four GEnx-powered Dreamliners, all to Japan Airlines (JAL), which currently operates the planes on routes out of Tokyo to Boston, Moscow and Delhi.

Kennedy said JAL is "very happy" with the performance of its GEnx engines, which he said have proved "extremely reliable."

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

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