Federal investigators found “fatigue cracking” on an engine disk that broke apart while an American Airlines flight was attempting to take off at Chicago O’Hare Airport last Friday.
According to the National Transportation Safety Board, the right engine’s high pressure turbine disk fractured into at least four pieces as the Boeing 767-300 reached an airspeed of 128 knots on the runway. The engine failure caused a fuel fire, melting part of the right wing of the aircraft. Passengers escaped the plane on emergency slides as large plumes of smoke billowed into the air.
“One of the fractures exhibited features consistent with fatigue cracking initiating at an internal inclusion near the forward side of the hub’s inner bore,” the NTSB said on Friday in an investigative update.
American Airlines Flight 383, with 161 passengers and nine crew members, was departing for Miami when the incident occurred during takeoff. Twenty people were taken to local hospitals with minor injuries.
One part of the disk was flung almost 3,000 feet and found at a UPS warehouse. Engine and wing debris were also found in a gouge mark on the runway, investigators said.
General Electric, which manufactured the engine, said it is cooperating with the NTSB and has told operators of aircraft with the CF6 engine that a material anomaly was found in the disk. In a letter sent to operators on Friday, GE said it identified a “limited number of closely related” engine parts and that only one is still in operation.
“We are currently working with the operator to accomplish removal of the remaining part in service,” GE said in the letter. There are more than 4,000 CF6 engines currently in service, GE said, and the CF6 engine has accumulated more than 400 million flight hours.
The NTSB said the failed disk had been used for 10,984 cycles and had a life limit of 15,000 cycles. Investigators are reviewing American’s engine maintenance and Boeing’s and GE’s manufacturing records.
American declined to comment as the incident is being investigated. The carrier has 35 Boeing 767-300 aircraft in its fleet with the GE engine. American has been gradually retiring the 767s, which have an average fleet age of 21 years.
The ongoing investigation will focus on “metallurgical examinations” of the disk, the NTSB said. The disk, along with flight data recorders, were sent to the NTSB’s lab in Washington D.C. earlier this week.
GE said it has not experienced a failure of the high pressure turbine disk in more than 30 years, noting that the disk is a rotating part that holds the second-stage turbine blades, operating in one of the hottest parts of the jet engine.
“Since the 1970s, the GE CF6 engine has been one of the workhorse jet engines of the airline industry, powering seven wide-body commercial jet models with industry-leading levels of reliability,” GE said in a press statement.