Federal investigators are focusing on fatigue cracks on a jet engine part that caught fire last week on an American Airlines plane that was seconds from lifting off at O'Hare International Airport, according to a Friday update.
Nine crew members and 161 passengers evacuated with just minor injuries Oct. 28, but photos of the incinerated right wing show how serious the situation was.
National Transportation Safety Board officials found that one of the steel engine disks on the Boeing 767 fractured into four pieces. One section pierced the right wing and catapulted 2,920 feet away, landing at a UPS warehouse.
The disk, which helps power the GE CF6 engine, exhibited signs of fatigue cracks, the NTSB reported. The disk "had 10,984 cycles and had a life limit of 15,000 cycles," officials said, adding they were reviewing engine maintenance and manufacturing records.
The airplane was operating at takeoff power at about 2:30 p.m. when the engine failed. Two seconds later, the aircraft slowed and automatic braking kicked in, the NTSB said.
Meanwhile a fuel leak in the engine ignited a fire under the right wing.
The GE CF6 engine has been described as a reliable "workhorse."
However, the Federal Aviation Administration has issued a number of airworthiness directives about the CF6 engine, including one in June 2016 in which officials told GE to replace accessory heat shield assemblies.
GE spokesman Rick Kennedy said the company "continually monitors and analyzes the performance of the CF6 fleet in service."
"Based on the engine fleet's service history, we are not aware of operational issues that would hazard the continued safe flight of aircraft powered by these engines," he said.
More than 4,000 of the engines are in service with more than 400 million flight hours, Kennedy added.
The FAA routinely issues airworthiness directives involving aircraft.