As authorities investigate why a GE engine failed and led to fire aboard an American Airlines jet Friday, records show federal authorities had asked the manufacturer to fix problems with that type of engine previously.
Twenty people were treated for minor injuries Friday afternoon after pilots aborted the takeoff to Miami and 161 passengers and nine crew members evacuated the Boeing 767-300 using the emergency chutes.
A disk in the engine, a GE CF6 model, failed, catapulting one component 2,920 feet away in a UPS warehouse and sending another piece one-third of a mile away on the airfield.
The Federal Aviation Administration has issued a number of air-worthiness directives about the CF6 engine, including one in June 2016 in which officials told GE to replace accessory heat shield assemblies.
The directive was prompted by reports of a "burn through" during an engine fire. In such a scenario, the existing shields can leave a large area near the main fuel pump without adequate protection, the agency stated, adding it was acting to "prevent an uncontrolled engine fire, and damage to the airplane," FAA records show.
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.
Air-worthiness directives occur regularly in the aviation industry as a precaution.
Experts speculated about a freak occurrence such as a bird being sucked into the engine or blown tire treads causing the problem, and they dismissed some internet chatter of sabotage.
"There's nothing to lead in that direction at this point," National Transportation Safety Board spokesman Peter Knudson said.
Generally, GE engines have performed well, said Lewis University aviation professor and commercial pilot William Parrot. The Boeing 767-300 also has a solid track record, he said.
The NTSB has transferred the failed engine parts to its laboratories, along with the flight data recorder, and is coordinating with GE, American Airlines, Boeing and others.
"They're going to be going through that with a fine-tooth comb," Parrot said.
Among many possibilities could be a bird or part of a tire tread being sucked into the engines, Parrot said. He noted that a Concorde jet crashed in July 2000 after pieces of a blown tire damaged a wing, affecting the fuel tanks and causing a catastrophic fire.
Foreign objects could compromise myriad operations on the aircraft from the engines themselves to fuel lines in the engines, or fuel tanks stored in the wings, Parrot explained.
Human error is the single-largest factor in airplane problems, University of Illinois Urbana-Champaign aviation security expert and professor Sheldon Howard Jacobson said.
"Mechanical is second-most frequent. Weather is third. Sabotage and terrorism is fourth. Given the volume of flights per day, and small number of reports of problems, one can see why air travel is as safe as it is," Jacobson said.
Photos of the plane, provided by an airport worker to ABC 7 Chicago, show the plane's right side badly charred with melted windows and a drooping and heavily damaged right wing.
The intensity of the fire that incinerated parts of the aircraft underscores the need for passengers to pay attention to flight instructions, no matter how banal they seem, said Jan Brown, a retired flight attendant and crew member on a United Airlines airplane that crashed into Sioux City, Iowa, in July 1989.
"People just assume, 'It's a beautiful day out today, I'll be able to see the exits.' Our day was a beautiful day, too," Brown said. "When I opened my eyes (after the crash landing), it was pitch black."