The National Transportation Safety Board (NTSB) in the US has said that signs of fatigue cracking were found at the high-pressure turbine disk in the General Electric (GE) engine of the failed American Airlines flight.

Last month, the Boeing 767-300 (N345AN) aircraft caught fire under its right wing at Chicago O'Hare International Airport due to a fuel leak from the damaged engine.

In its preliminary investigation report, NTSB said that nearly 6,550ft from the runway threshold, the aircraft experienced an uncontained failure of the right engine and came to complete halt around 9,225ft away from the runway.

However, all 161 passengers and nine crew were evacuated safely, with only minor injuries, reported Airwise.

"The aircraft experienced an uncontained failure of the right engine and came to complete halt around 9,225ft away from the runway."

According to the flight data recorder (FDR) data recovered after the incident, the right engine’s stage-two high-pressure turbine disk fractured into at least four pieces.

One of the fractured pieces went through the inboard section of the right wing, over the fuselage and into a UPS warehouse facility of the airport.

NTSB also noted that the turbine disk had 10,984 cycles and a life limit of 15,000 cycles.

The agency is still reviewing the engine maintenance and manufacturing records of the aircraft.

Currently being performed at the NTSB laboratory in Washington, DC, metallurgical examinations of the disk will focus on a detailed characterisation of the inclusion and the fracture surfaces.

Apart from NTSB, the US Federal Aviation Administration (FAA), American Airlines, Allied Pilots Association, Boeing, GE Engines, Transport Workers Union of America and Association of Professional Flight Attendants are involved in the investigation.

Image: Recovered stage two of high-pressure turbine disk pieces. Photo: courtesy of National Transportation Safety Board (NTSB).