NTSB: Boeing knew of engine-mount part failures years before UPS Louisville crash

The National Transportation Safety Board said Wednesday that Boeing documented four failures of a critical engine-mounting component on three aircraft as far back as 2011, but at the time concluded the defect would not threaten flight safety — years before a UPS cargo plane lost its left engine during takeoff in Louisville, Kentucky, on Nov. 4, 2025, killing 15 people.

The NTSB’s factual report raises questions about whether Boeing’s 2011 service letter — which recommended but did not require replacing the faulty part, and which the Federal Aviation Administration never elevated to a mandatory airworthiness directive — was an adequate response to a documented pattern of failures on aging aircraft.

What the NTSB found

The part under scrutiny is a spherical bearing race that helps secure engines to the wings of the MD-11 freighter. Investigators found the component broken in two pieces after the crash, along with cracks in the lugs that held it in place. The NTSB said those cracks had not been detected during routine maintenance.

Boeing’s 2011 documentation described four previous failures of the same part on three separate planes, but the company “determined it would not result in a safety of flight condition,” the NTSB said. The MD-11 and its predecessor, the DC-10, were originally built by McDonnell Douglas, which Boeing later acquired.

The most recent detailed inspection of the UPS plane’s engine-mounting hardware had occurred in October 2021. Under the existing maintenance schedule, the next such close inspection was not due for approximately 7,000 more takeoffs and landings.

A service letter, not a directive

Boeing’s 2011 service letter recommended replacing the spherical bearing race with a redesigned part less likely to fail. But the notice still allowed operators to install another older-style bearing rather than the improved component. Because the document was a service letter rather than an FAA airworthiness directive, compliance was not required.

Former federal crash investigator Alan Diehl said the structure left operators with an inadequate remediation option.

“As the investigation continues, the NTSB will have to address whether this service bulletin was an adequate solution to a known problem which could have had catastrophic results,” Diehl said. “The UPS crash highlights the need for increased maintenance measures on older airframes.”

Former FAA and NTSB crash investigator Jeff Guzzetti said the 2011 characterization contradicted an earlier bulletin. A McDonnell Douglas service bulletin issued in 1980 — following a fatal DC-10 crash in Chicago — had classified failures of the same spherical bearing race as a “safety of flight condition,” he said.

“I just think it raises questions regarding the adequacy of the severity of the 2011 service letter, and it also raises questions about how UPS incorporated that information and acted upon it,” Guzzetti said.

The crash

The 34-year-old MD-11 freighter was bound for Hawaii when the left engine separated from the wing while the aircraft was rolling down the runway at Louisville’s Muhammad Ali International Airport. The plane reached only 30 feet of altitude before crashing into industrial buildings just beyond the runway, generating a fireball visible for miles. Three crew members aboard and 12 people on the ground were killed.

The NTSB’s Wednesday release is a factual report and does not assign a probable cause. Investigators have not yet determined the precise sequence of events that caused the engine to separate. The agency’s final report, which will include probable cause findings, typically is not released until more than a year after a crash.

Photos released by the NTSB show flames erupting as the rear of the engine began to detach before it flew up and over the wing. The report made clear that neither of the plane’s two other engines was on fire before the crash.

Historical echo

The Nov. 4, 2025 accident echoes a May 1979 crash of American Airlines Flight 191 at Chicago’s O’Hare International Airport, in which the left engine also separated during takeoff, killing 273 people. That crash led to the temporary worldwide grounding of 274 DC-10s. Investigators ultimately attributed it to damage from improper maintenance procedures rather than a design flaw. The MD-11 is derived from the DC-10.

Airlines stopped operating the MD-11 commercially years ago because newer aircraft are more fuel-efficient. The type had continued as a cargo hauler for carriers such as UPS and FedEx. All MD-11s in service and 10 related DC-10s have been grounded since the November crash.

Litigation and response

Attorney Brad Cosgrove of the Clifford Law Offices, which filed the first lawsuit arising from the crash, said the NTSB’s factual report supports the plaintiff’s position.

“I think that this even further demonstrates that there was warning signs that predated the crash that any reasonable organization should have utilized to make sure that the Louisville crash didn’t happen,” Cosgrove said.

UPS spokesperson Jim Mayer expressed condolences in a statement Wednesday.

“We remain profoundly saddened by the Flight 2976 accident,” Mayer said. “Our thoughts continue to be with the families and Louisville community who are grieving, and we remain focused on the recovery effort.”

Boeing, UPS and the FAA all declined to comment on the factual report, citing the ongoing NTSB investigation. Boeing and UPS both expressed condolences to victims’ families.