Boeing Flagged Engine-Mount Defect 15 Years Before Fatal UPS Crash, NTSB Reveals
WASHINGTON, United States — The engine-mount component that fractured and triggered the catastrophic separation of a cargo jet’s left engine during takeoff last November had been flagged by Boeing nearly 15 years earlier, federal investigators disclosed this week. In a mid-investigation update released Wednesday, the National Transportation Safety Board revealed that Boeing issued a service letter in February 2011 documenting four prior failures of the identical spherical bearing race on three different MD-11 aircraft.
Remarkably, the plane manufacturer concluded at the time that such failures would not pose a safety-of-flight condition.
The bearing race sits within the engine-to-pylon mounting assembly, a critical junction that secures each powerplant to the aircraft’s wing structure. In each of the four documented incidents, the collar-like component suffered fatigue cracking that initiated at a design recess groove on its interior surface, ultimately splitting along its circumference. NTSB investigators found that the bearing race recovered from the Louisville accident exhibited the very same failure pattern.
UPS Flight 2976, a 34-year-old McDonnell Douglas MD-11F freighter operating as a domestic cargo service bound for Honolulu, crashed seconds after liftoff from Louisville Muhammad Ali International Airport on Nov. 4. The jet’s left GE Aerospace CF6 turbofan and its pylon assembly tore away from the wing during the takeoff roll, igniting a massive fireball. The crippled aircraft never climbed beyond roughly 30 feet above runway elevation before slamming into an industrial complex just past the airfield’s perimeter fence. Three pilots aboard the aircraft perished alongside 12 people on the ground—making it the deadliest aviation disaster in the United States since the Sept. 11 attacks.
The Boeing service letter, dated Feb. 7, 2011, instructed operators to visually inspect the spherical bearing assembly as part of routine pylon maintenance scheduled at 60-month intervals. It also updated the MD-11’s maintenance manual accordingly and recommended—but did not mandate—installation of a redesigned bearing lacking the problematic groove. Crucially, the bulletin did not prohibit operators from replacing a defective grooved bearing with another airworthy component of the original design.
“According to the service letter, a review of the spherical bearing failure by Boeing determined it would not result in a safety of flight condition,” the NTSB stated in its six-page update.
Whether UPS incorporated the 2011 guidance into its own maintenance program remains under active investigation. Investigators are also examining correspondence between Boeing and the Federal Aviation Administration that preceded and followed the service letter’s issuance. Boeing acquired McDonnell Douglas in 1997, assuming responsibility for the continued airworthiness of the former manufacturer’s in-service fleet, including the MD-11.
The accident aircraft last underwent a general visual inspection of the relevant engine-mount components in October 2021. Under UPS protocols, the next detailed examination wasn’t scheduled until approximately 7,000 additional flight cycles had accumulated. Maintenance records show the spherical bearings were lubricated on Oct. 18, 2025—just over two weeks before the crash.
Former FAA and NTSB investigator Jeff Guzzetti noted an apparent inconsistency in Boeing’s characterization of the defect’s severity. A McDonnell Douglas service bulletin from 1980 had identified spherical bearing race failures as a safety-of-flight condition, he observed, raising questions about why Boeing’s 2011 letter adopted softer language.
“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 told reporters.
The parallels to an earlier tragedy have not escaped investigators’ attention. On May 25, 1979, American Airlines Flight 191—a McDonnell Douglas DC-10, the MD-11’s predecessor—crashed moments after departing Chicago O’Hare when its left engine and pylon assembly separated during rotation. That accident claimed 273 lives and remains the deadliest aviation disaster on U.S. soil outside of the Sept. 11 attacks. The NTSB ultimately attributed the Chicago crash to improper maintenance procedures that damaged the pylon structure, and the DC-10 fleet was temporarily grounded worldwide.
But there’s a significant distinction. The 1979 failure stemmed from airline maintenance workers using a forklift to remove and reattach the engine and pylon as a single unit—a shortcut that stressed critical components. In the Louisville case, investigators have yet to identify any such procedural deviation. The failure mode appears instead to involve inherent fatigue characteristics of the bearing race design itself.
Boeing and UPS declined to comment substantively on the latest findings, citing the ongoing investigation. Both companies expressed continued condolences to the families of victims.
“We remain profoundly saddened by the Flight 2976 accident,” UPS spokesperson Jim Mayer said in a statement. “Our thoughts continue to be with the families and Louisville community who are grieving.”
The FAA grounded all MD-11 and MD-11F cargo aircraft on Nov. 8, four days after the crash, requiring comprehensive inspections and corrective actions before any return to service. That directive subsequently expanded to include DC-10 freighters with similar engine-pylon designs. FedEx, which operates the world’s largest MD-11F fleet with 34 aircraft, expects the grounding to persist until spring 2026. The company has disclosed $175 million in additional costs from chartering replacement aircraft and shifting cargo volumes to ground transportation during the peak holiday shipping season.
Multiple lawsuits have been filed against UPS, Boeing, and engine manufacturer GE Aerospace on behalf of crash victims. Attorneys representing claimants have characterized the 2011 service bulletin as evidence that the manufacturers possessed foreknowledge of a potentially catastrophic defect.
The NTSB has not yet determined a probable cause. Its final report, which typically takes more than a year to complete, will examine aircraft performance characteristics following engine separation, the adequacy of Boeing’s maintenance guidance, UPS’s compliance with that guidance, and the regulatory oversight exercised by the FAA.
Investigators continue working to understand why the jet failed to achieve a normal climb rate after losing its left engine—a scenario that modern aircraft are generally designed to survive.
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