(Bloomberg) -- An engine on an American Airlines plane that exploded on a Chicago runway Oct. 28, triggering a massive blaze, had an apparent manufacturing defect, U.S. investigators said Friday.
A disk within the General Electric Co. CF6-80 engine had an “internal inclusion,” meaning some type of foreign debris was embedded within the special alloy designed to withstand the heat and high stresses of a jet engine, the U.S. National Transportation Safety Board said in a statement.
GE believes it has identified the “limited number” of disks manufactured at the same time that may have the same flaw and only one other remains in operation, the company said in a letter Friday to carriers. “We are currently working with the operator to accomplish removal of the remaining part in service,” said the letter, obtained by Bloomberg.
The NTSB statement didn’t say whether the flaw posed a risk in other engines. GE didn’t immediately respond to an e-mailed request for comment.
In a statement earlier Friday, GE said it hasn’t experienced such a failure in parts made with the same alloy in more than 30 years. There are more than 4,000 of the various CF6 engines in service and they’ve flown more than 400 million hours, GE said.
“Given the number of incidents that have occurred, I wouldn’t say it rises to the level of a fleet issue,” said Robert Mann, president of aviation consultant R.W. Mann & Co. “But it’s something they obviously have to think about -- how that occurred, why that occurred.”
GE and the unnamed supplier of the Inconel 718 alloy, commonly used in the hot section of engines, are reviewing production records for NTSB investigators, GE said in a statement.
The 170 people aboard American Airlines Flight 383, a Boeing Co. 767 at Chicago’s O’Hare International, raced out of left-side exits after an orange fireball erupted on the right of the plane. The engine had blown up during a takeoff attempt, triggering a fuel leak and the fire. At least 20 people suffered minor injuries during the evacuation, according to the NTSB.
The CF6-80 engine failed so violently that pieces of the spinning disk flew 2,920 feet (890 meters) away, striking a warehouse, the NTSB said in a briefing Saturday. Jet engines are encased in armor and have other safeguards to ensure that shrapnel can’t escape in a failure, so the NTSB will try to determine why those protections failed. The plane was accelerating for takeoff and pilots were able to stop on the ground before lifting off.
American Airlines declined to comment because of the continuing investigation, said Ross Feinstein, a spokesman for the carrier.
The disk, located in the rear portion of the engine, where burning fuel races past fan blades to spin the turbine, broke into at least four pieces, according to NTSB. It was designed to withstand at least 15,000 startups and had only been used 10,984 times, the NTSB said.
In its letter to operators of the same engine model, GE said it had identified “a material anomaly” that appeared to be linked to the failure. “Although the investigation is still under way, a limited number of closely related CF6-80C2 parts have already been identified, only one of which is still in operation,” GE said in the letter.
The engine involved in the American fire was built in 1997, according to GE.
“Since the 1970s, the GE CF6 engine has been one of the workhorse jet engines of the airline industry, powering seven widebody commercial jets models with industry-leading levels of reliability,” GE said in its earlier release.
It has been used on many aircraft, including the Airbus Group SE A330 and Boeing’s MD-11, 747 and 767. The power plants have accumulated more than 100 million flights since their introduction, according to the company.
While there have been dozens of safety alerts on various models of the engine issued by NTSB or the Federal Aviation Administration, none in the past 10 years appear to have zeroed in on the component that failed, according to agency records.
The American flight had accelerated to 154 miles (248 kilometers) an hour before the pilots began applying the brakes, according to NTSB. It came to a stop about 25 seconds later. Fire crews arrived on scene and started applying foam to the burning jet fuel within 2 minutes and 51 seconds of being notified of the emergency, NTSB said.
The fire burned so hot that the right wing partially collapsed.
If contamination exists within metal structures, that can weaken them and allow a crack to form, according to previous NTSB investigations. Repeatedly flexing or stressing the crack can cause it to grow in what is known as fatigue cracking. The NTSB said it found evidence of fatigue in the CF6 disk fragments it examined.
The NTSB is also investigating another so-called uncontained engine failure that occurred on Aug. 27 on a Southwest Airlines Co. plane, which was forced to make an emergency landing in Pensacola, Florida.
The CFM56 engine in the Southwest incident was built by CFM International Inc., a joint venture between GE and Safran SA. The CFM56 family, used on narrowbody aircraft, is separate from the CF6.