Cracked Component in Fatal UPS MD-11 Accident Was Flagged by Boeing in 2011
The National Transportation Safety Board (NTSB) investigation into the fatal crash of a UPS McDonnell Douglas MD-11 cargo plane at Louisville, Kentucky airport has focused on a critical technical element that had been identified by the manufacturer itself over a decade earlier. The finding reopens an uncomfortable debate for the industry: when does a fatigue problem cease to be “maintainable” and become a direct threat to flight safety?
The accident, which occurred in November 2025, left 15 people dead, including three crew members, and led to the grounding of the MD-11 model for cargo operations. The aircraft crashed following an inflight fire, in a sequence investigators are still reconstructing.
Key Component: Fatigue Cracks in the Left Pylon
The “Bearing Race” Under Scrutiny
According to the NTSB’s preliminary report, the crashed aircraft had fatigue cracks in a support structure of the left pylon, the assembly that connects the wing to one of the engines. The affected part is known as a bearing race, a structural component that plays an essential role in the integrity of the engine mounting.
This was not an unknown phenomenon.
In 2011, Boeing had issued a service letter documenting four previous failures of the bearing race on three different aircraft. That communication recommended periodic visual inspections, typically every five years, but did not classify the problem as a “safety-of-flight issue”—meaning it was not considered an immediate risk to flight safety.
That point is now central to the investigation.
When Structural Fatigue Ceases to Be a Maintenance Detail
A Technical Warning That Gains Weight in Retrospect
For aviation safety expert Anthony Brickhouse, cited in the NTSB update, Boeing’s bulletin already warned of a scenario of structural fatigue.
“If fatigue is not managed correctly, it can obviously become a flight safety problem.”
The statement summarizes the technical and regulatory dilemma: fatigue is progressive, silent, and, in many cases, detectable only if inspection intervals and severity criteria are adequate. The 2011 document assumed visual inspections were sufficient, a premise now being reviewed in light of the accident.
Fire in the First Engine and Anomalies in the Second
A Still-Incomplete Chain of Events
The NTSB additionally confirmed that:
- The MD-11’s first engine caught fire in flight.
- The second engine exhibited thrust anomalies.
Under normal conditions, a trijet like the MD-11, operating with two fully functional engines, should be capable of maintaining climb. The fact that this did not occur reinforces the hypothesis of a cascade of failures, beyond a single isolated event.
Investigators are now analyzing the possible ingestion of debris or fragments, a common line of inquiry when structural failures, engine fire, and performance loss combine.
With information from Reuters
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