An aircraft that crashed in flames in Kentucky in November had a structural flaw that had been identified by Boeing on 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 was preparing to take off from Louisville. The plane briefly lifted off from the runway before hurtling out of control into an industrial area. Fifteen people were killed, including three crew members and twelve individuals on the ground.
In an update, the US National Transportation Safety Board (NTSB) revealed that cracks found in the engine mounting assembly had previously occurred on several other aircraft.
At the time, the manufacturer responsible for the aircraft, Boeing, concluded that the issue would not result in a safety of flight condition. The MD-11 is a relatively elderly design that was originally produced by McDonnell Douglas, which Boeing acquired in 1997. The last MD-11 was produced in 2001, yet Boeing has continued to provide parts and service support.
Following the Kentucky disaster, the NTSB issued a preliminary report drawing attention to the cracks in the engine attachment mechanism. Its latest update goes further, describing fractures due to fatigue – or repeated stresses – in a critical bearing, as well as the mounting it is meant to sit in.
The report indicates that Boeing had previously found failures of the same part on four occasions, affecting three different aircraft. In 2011, the company sent a service letter to operators warning them of its findings. This is a non-legally-binding document meant to alert operators about important safety or maintenance information.
In this specific case, Boeing recommended that the part be included in a general visual inspection every five years, along with changes to the inspection procedure outlined in the aircraft maintenance manual, and noted a revised bearing assembly that could be fitted, even though this was not mandatory.
Tim Atkinson, a former air accident investigator turned aviation safety consultant, remarked that the NTSB's update is deeply concerning. The structure concerned is not decorative; it's an essential part of the mechanism that attaches the engine to the wing and bears loads like thrust and drag, he explained. It's extraordinary that Boeing concluded that failure of this part would not have safety consequences.\p>
Boeing has faced significant scrutiny in recent years regarding internal processes. Criticisms have particularly focused on the design failures of its 737 Max, implicated in two tragic accidents that together claimed 346 lives. Quality controls at Boeing factories have also been under the microscope after a door panel fell off a brand new 737 Max shortly after takeoff in early 2024.
In a statement, Boeing expressed its commitment to supporting the NTSB investigation, extending condolences to the families affected by the crash.
The NTSB continues its investigation into the Kentucky crash and has yet to issue firm conclusions on the cause of the accident, awaiting the publication of the final report.
