The US National Transportation Safety Board (NTSB), in its investigation into the UPS-operated MD-11F cargo aircraft that crashed in flames in the state of Kentucky in November, drew attention to a critical structural flaw. According to investigators, the aircraft involved in the accident had a structural issue that Boeing had identified on similar aircraft approximately 15 years ago.
The UPS MD-11F cargo aircraft briefly lifted off the runway after one of its engines separated from the wing while preparing for departure from Louisville. Shortly after take-off, the aircraft lost control and crashed into an industrial area. A total of 15 people lost their lives in the accident, including three crew members and 12 people on the ground.
Cracks Previously Observed in the Engine Mount Assembly
According to the NTSB’s updated report, cracks in the engine mount assembly that caused the accident had also been detected previously on several other MD-11 aircraft. However, the aircraft manufacturer Boeing had concluded at the time that this issue “did not pose a risk to flight safety.”
The MD-11 model is a relatively old design originally developed by McDonnell Douglas. Boeing acquired the company in 1997. The last MD-11 aircraft rolled off the production line in 2001, but Boeing has continued to provide parts and maintenance support to this day.
“Fatigue-Related Fracture” Finding
Following the Kentucky accident, the NTSB released a preliminary report highlighting cracks in the engine attachment mechanism. In the latest update, the investigation went further, stating that “fatigue” or fracture due to repeated stresses was identified in a critical bearing housing and in the mounting component in which this housing was installed.
The report also noted that Boeing had detected failures in the same component on four other aircraft. In 2011, the company had sent operators a non-mandatory “service letter” drawing attention to the issue.
In this letter, Boeing recommended that the component be included in a general visual inspection every five years, that changes to the inspection procedures in the maintenance manual be taken into account, and that a revised bearing assembly be used, although this was not mandatory.
Strong Criticism from Experts
Tim Atkinson, a former air accident investigator who currently works as an aviation safety consultant, described the NTSB update as “disturbing.”
- Atkinson stated,
- “This structure is not decorative; it is a fundamental part of the mechanism that connects the engine to the wing and carries loads such as thrust and drag.”
He described Boeing’s assessment that failure of this component would not have safety consequences as “extraordinary.”
Boeing’s Safety Processes Back in the Spotlight
Boeing’s internal safety and quality processes have been the focus of intense criticism in recent years, particularly following the 737 Max accidents. In the two accidents that occurred in 2018 and 2019, 346 people lost their lives.
In addition, in early 2024, the separation of a door panel shortly after take-off on a newly delivered 737 Max aircraft once again brought the company’s production and quality control processes into question.
In a statement, Boeing said:
“We continue to support the investigation being conducted by the NTSB. We extend our deepest condolences to the families who have lost loved ones and express our sympathy to all those affected.”
The NTSB stated that the investigation is ongoing and that the final report on the cause of the accident has not yet been prepared.
