A plane that crashed in Kentucky in November had a structural flaw that Boeing identified in similar planes 15 years ago, according to investigators.
The MD-11F freighter, operated by UPS, crashed after one of its engines separated from the wing as it prepared to take off from Louisville.
The plane briefly lifted off the runway, before running out of control into an industrial area. Fifteen people died as a result, including three crew members and 12 on the ground.
In a update reportthe US National Transportation Safety Board (NTSB) disclosed that the cracks found in the engine mounting assembly had previously occurred in several other aircraft.
At the time the manufacturer responsible for the aircraft, Boeing, concluded that the issue “does not result in a safe flight situation”.
The MD-11 is a relatively old design originally developed by McDonnell Douglas. Boeing acquired the company in 1997.
The last MD-11 rolled off the production line in 2001, but Boeing continues to provide parts and service support.
After the Kentucky disaster, the NTSB issued a preliminary report that drew attention to cracks in the engine’s linkage mechanism. Its latest update continues, describing fractures due to evidence of “fatigue” – or repeated stresses – in a critical bearing, as well as the mounting it targets.
It pointed out that Boeing had previously found failures in the same part four times, affecting three different planes. In 2011, the company sent a “service letter” to operators alerting them to its findings. This is a non-legally binding document used to alert operators of important safety or maintenance information.
In this case, Boeing recommends that the part be included in a general visual inspection every five years. It also points to changes in the inspection procedure contained in the aircraft maintenance manual, and draws attention to a revised bearing assembly that could be fitted – although it is not mandatory.
Tim Atkinson, a former air accident investigator who now works as an aviation safety consultant, said the NTSB update made disturbing reading.
“The structure in question is not decorative, it is an integral part of the mechanism that attaches the engine to the wing, and carries loads such as push and drag,” he explained.
“It is remarkable that Boeing has concluded that a failure in this part has no safety consequences,” he said.
Boeing’s internal processes have come under fire several times in recent years.
Criticism has focused on how the design of its 737 Max included faulty software that was linked to two accidents, in 2018 and 2019, that cost 346 lives.
Quality controls at its factories are also under scrutiny, after a door panel fell off a new 737 Max shortly after takeoff in early 2024.
In a statement, Boeing said: “We continue to support the investigation led by the NTSB. Our deepest condolences go out to the families who lost loved ones and our thoughts remain with all those affected.”
The NTSB investigation is ongoing. It has not yet issued any firm conclusions about the cause of the accident, and likely won’t until its final report is published.