A critical component involved in the fatal UPS cargo plane crash in Kentucky had been identified as a potential issue by Boeing more than a decade ago, according to new findings from the National Transportation Safety Board (NTSB).
The NTSB revealed on Wednesday that a cracked part was discovered on the UPS MD-11 cargo jet that crashed near Louisville Muhammad Ali International Airport in November 2025. The investigation has identified fatigue cracks in a support structure on the left pylon—the critical component that connects the aircraft’s wing to its engine—specifically within a part known as the bearing race.
The crash, which occurred on November 4, 2025, resulted in the deaths of 15 people, including three crew members. The incident has had significant repercussions for the aviation industry, leading to the grounding of the MD-11 cargo jet model.
The NTSB Investigation and Findings
The NTSB’s recent update provides a clearer, albeit harrowing, picture of the mechanical failures that preceded the crash. Investigators found that the fatigue cracks were located in the bearing race of the left pylon. This structural failure appears to have been central to the aircraft’s loss of control.
Data from the investigation suggests a cascading failure during the flight. The NTSB reported that the aircraft’s first engine caught fire during the incident. Investigators noted “anomalies in the thrust” of the second engine. For a three-engine aircraft, the ability to maintain flight and climb typically relies on at least two fully operational engines; however, the combination of the fire and thrust irregularities proved catastrophic.
The crash near Louisville occurred shortly after takeoff, prompting local authorities to issue a shelter-in-place order for all residents within a five-mile radius of the airport due to the intensity of the fire and smoke.
A Decade-Old Warning: The Boeing Service Letter
Perhaps most significant to the ongoing investigation is the revelation that Boeing had previously flagged issues with this specific component. According to the NTSB, a Boeing service letter issued in 2011 documented similar concerns.
The 2011 letter noted that there had been four previous failures of the bearing race across three different aircraft. At that time, the failures required visual inspections, but Boeing did not classify the matter as a “safety-of-flight” issue. The documentation indicated that the part would typically undergo inspection every five years.
Air safety expert Anthony Brickhouse noted the gravity of these findings, emphasizing the risks associated with structural wear. “If fatigue isn’t handled properly, obviously it can become a safety-of-flight issue,” Brickhouse stated, highlighting how long-term structural fatigue can transition from a maintenance concern to a terminal mechanical failure.
While Boeing has stated it continues to support the NTSB-led investigation, the company has not commented directly on the contents of the 2011 service letter. The Federal Aviation Administration (FAA) has also declined to comment on the matter.
Technical Context: Understanding Pylon Fatigue
To understand the implications of the NTSB’s findings, it is necessary to look at the role of the engine pylon. The pylon is the structural bridge between the wing and the engine. It must withstand immense stress, including the weight of the engine, the thrust generated during flight, and the vibrations inherent in jet propulsion.
The bearing race is a vital part of this support structure. When fatigue cracks develop in such a high-stress area, the structural integrity of the connection between the wing and the engine is compromised. If the pylon fails, the engine can become detached or lose its ability to provide stable thrust, as was observed during the UPS Flight 2976 incident.
The transition from “visual inspection” requirements to a fatal structural failure raises critical questions for aviation regulators regarding the adequacy of current inspection intervals for aging cargo fleets, particularly for models like the MD-11 that have been in service for decades.
Key Takeaways from the NTSB Update
- Casualties: 15 people died in the November 2025 crash, including three crew members.
- Primary Failure: Fatigue cracks were found in the bearing race of the left pylon.
- Historical Precedent: A 2011 Boeing service letter flagged four previous bearing race failures in three aircraft.
- Engine Status: The first engine caught fire, and the second engine exhibited thrust anomalies.
- Regulatory Action: The MD-11 cargo jet model has been grounded following the incident.
What Happens Next?
The NTSB investigation remains active as officials work to determine why the fatigue cracks were not detected during routine maintenance and whether the five-year inspection cycle recommended in the 2011 service letter was sufficient to prevent such a failure.
The focus of upcoming proceedings will likely center on the maintenance records of the specific UPS MD-11 involved and the efficacy of the visual inspection protocols used for the bearing race component. The aviation community and regulators will be watching closely to see if this leads to new mandates for the MD-11 fleet or broader changes to how fatigue in pylon structures is monitored globally.
We will continue to provide updates as the NTSB releases further findings from its investigation.
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