Fatigue Cracks Found in UPS MD-11 Wreckage Offer Major Clue in Deadly Kentucky Crash

U.S. investigators have found evidence of fatigue cracks in a key structural component of the UPS MD-11 cargo jet that crashed in Louisville, Kentucky, on November 4, killing 14 people, the National Transportation Safety Board (NTSB) said Thursday Nov. 20. The discovery marks a significant step in determining the root cause of the disaster.

According to the NTSB’s preliminary report, the cracks were located in the left engine pylon’s aft mount lug, which connects the engine to the wing. Investigators also found signs of overstress failure, indicating that one side of the pylon’s support structure had weakened over multiple flights until it fractured, leading to catastrophic engine separation during takeoff.

“This is a major clue,” said U.S. air-safety expert Anthony Brickhouse, explaining that such cracks develop gradually and may have gone unnoticed during prior maintenance checks. Aviation analyst John Cox added that fatigue cracks progressively weaken support structures until “the force overcomes what the structure can withstand.”

The 34-year-old MD-11 had recently undergone maintenance in Texas at a facility operated by Singapore’s ST Engineering, and investigators are reviewing the aircraft’s inspection history. The NTSB noted that the jet had not reached the threshold requiring a special detailed inspection of the affected part.

The report draws parallels to the 1979 crash of American Airlines Flight 191, when a DC-10 lost its left engine and pylon assembly during takeoff from Chicago O’Hare. In both cases, investigators identified fatigue cracks in the pylon mount as the initiating failure.

In response, both UPS and FedEx grounded their MD-11 fleets earlier this month following Boeing’s recommendation, while the Federal Aviation Administration (FAA) issued emergency directives temporarily grounding MD-11, MD-10, and DC-10 aircraft sharing similar designs.

NTSB Chair Jennifer Homendy said Boeing is conducting additional structural modeling and stress testing as part of the ongoing investigation. A final report is expected within a year, but the early findings underscore growing concerns over the aging MD-11 fleet and the risks associated with fatigue-related structural failures in older cargo aircraft.

Sources: AirGuide Business airguide.info, bing.com, reuters.com