The stage two high-pressure turbine disk of the GE Aviation CF6 turbofan that failed last week on an American Airlines Boeing 767-300ER in Chicago fractured into at least four pieces, according to details and photographs released by the US National Transportation Safety Board (NTSB).
The board also determined that the turbine disk had evidence of fatigue cracking, it says in a 4 November investigation update.

Recovered pieces of the CF6's stage two high-pressure turbine disk

At least one disk piece punctured the aircraft's right wing, flew over the aircraft's fuselage and landed at a UPS warehouse about 0.9km (0.56 mile) away, the board says.

The uncontained failure of the right CF6-80C2B6 engine on 28 October occurred at an airspeed of 128kt (237km/h) and at takeoff power.

Location of the CF6's disk fragments

The aircraft, registration N345AN, was operating American flight 383 to Miami. The failure happened when the aircraft was 1,991m (6,550ft) from the threshold of runway 28R, says the NTSB.

An examination of the disk pieces determined that "one of the fractures exhibited features consistent with fatigue cracking initiating at an internal inclusion near the forward side the hub's inner bore", says the NSTB. "Ongoing metallurgical examinations of the disk will focus on detailed characterisation of the inclusion and the fracture surfaces."

The location of the fatigue crack on the CF6's disk

The disk had a life limit of 15,000 cycles and had accumulated 10,984 cycles at the time of the failure, it adds.

Two seconds after the failure, the aircraft now travelling at 134kt, the left and right engine throttles were pulled back and maximum auto-braking was applied, the NTSB says.

The aircraft stopped on the runway about 2,804m (9,225ft) from the threshold and 25s after the throttles were reduced, it says.

"As a result of the uncontained engine failure, a fuel leak resulted in a pool fire under the right wing," says the NTSB's update.

Nine crew members and 161 passengers evacuated as the 767's right side was ablaze in fire.

In response to the NTSB update, GE Aviation says the turbine disk that fractured is made of a material called Inconel 718, which is commonly used in the hot section of jet engines.

"GE Aviation has not experienced a failure from an engine component caused by an anomaly in Inconel 718 material in more than 30 years," says a GE Aviation spokesperson.

The company and its supplier will provide production records from the lot of material used to produce the particular disk to the NTSB, he adds.

More than 4,000 CF6 engines are in service and have accumulated more than 400 million flight hours, he notes.

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