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In a mid-investigation update on the November crash of a McDonnell Douglas-built MD-11 in Louisville, Kentucky, the U.S. National Transportation Safety Board said on Jan. 14 that cracking discovered in a spherical bearing assembly from the accident aircraft “appears to be consistent” with an issue identified by Boeing almost 15 years ago.
The assembly in question is part of the pylon aft mount bulkhead that, along with the forward mount bulkhead and thrust link assembly, attaches the engine pylon to the wing. In the Louisville crash, airport surveillance videos showed the MD-11’s left engine and pylon separating from the wing shortly after takeoff.
The NTSB’s preliminary report on the accident, released Nov. 20, revealed that on the left pylon aft mount bulkhead, the forward and aft lugs that house the spherical bearing assembly had fractured and separated. The spherical bearing’s outer race, which contains the ball bearing and allows it to move independently of the surrounding parts, had also fractured around its circumference.
In its latest update, the NTSB said it found evidence of fatigue cracking on the interior surface of the bearing race, originating in a specific area of the race. The board said the assembly’s design and failure mode appear to be consistent with a 2011 Boeing service letter that informed operators of four previous bearing race failures on three different airplanes.
As a part of that service effort, the plane maker, which inherited the MD-11 product line in 1997, moved to include visual inspection of the part in a regular 60-month maintenance cycle and “recommended” installation of a new part design to mitigate the issue. However, Boeing did not require the installation of that new design, having previously determined that failure of the bearing race would “not result in a safety of flight condition.”
The update does not draw any conclusions about the role the bearing race failure may have played in the crash. The NTSB said its investigation is ongoing and includes reviewing how the service letter was incorporated by UPS as well as correspondence between Boeing and the FAA on the topic, among other things.
The MD-11 has been grounded since Nov. 8, along with a tiny group of remaining MD-10s and DC-10s, pending an inspection regime or other possible modifications to the aircraft that have not yet been prescribed by the Federal Aviation Administration to return the aircraft to service. The MD-11 only operates as a freighter with UPS, FedEx Express and Western Global Airlines. The November crash killed all three crew members on board the MD-11 and at least 12 additional people on the ground. Dozens more were injured.
“We continue to support the investigation led by the NTSB,” a Boeing spokesperson told TAC in an emailed statement. “Our deepest condolences go out to the families who lost loved ones and our thoughts remain with all those affected.”
A UPS spokesperson declined to comment on the NTSB’s update but said, “We remain profoundly saddened by the Flight 2976 accident. Our thoughts continue to be with the families and Louisville community who are grieving, and we remain focused on the recovery effort.”
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