UPS never required the detailed inspections necessary to identify the problem that led to an engine detaching from one of its planes before a fatal crash, despite Boeing recommending such checks years earlier, according to new documents released by crash investigators.
The engine fell off a UPS MD-11 freighter last November while accelerating for takeoff at Louisville’s Muhammad Ali International Airport, resulting in the deaths of all three pilots and 12 individuals on the ground. An additional 23 people were injured.
Documents submitted to the National Transportation Safety Board (NTSB) indicate that UPS did not mandate enhanced bearing inspections within the pylons that attach engines to the wings of its MD-11 fleet because Boeing had inaccurately stated that a failure of these bearings would not compromise flight safety. Consequently, these enhanced inspections were never required.
At investigative hearings in May, the specific failures that prevented mechanics from closely examining the critical components securing the engines to the wings were highlighted. The documents made public Wednesday offer further details on the matter.
While the NTSB’s final report on the cause of the crash is not expected until late this year or early next, UPS stated that "once the pylon separated from the aircraft, the crash was inevitable."
Acknowledged Misunderstandings and Shared Responsibility
Officials from Boeing and the Federal Aviation Administration (FAA) acknowledged during the hearings that they had underestimated the risks associated with the potential failure of a steel bearing and metal sheath within the engine mount. They did not initially realize this could lead to the breakage of the lugs anchoring the engines to the MD-11’s wings. These bearings are located deep within the pylons, making detection without engine removal difficult.
Aviation safety expert Jeff Guzzetti suggested that the actions of Boeing, UPS, the FAA, and the maintenance company STE San Antonio Aerospace collectively contributed to the crash. He noted that "there’s just lots of subtleties and semantics that these four entities are using. But in the end, this got missed and to some degree, all four have some role to play in that." Guzzetti, a former crash investigator for both the NTSB and FAA, emphasized that "safety is a shared responsibility, and I think the NTSB’s task now is to apportion that responsibility."
According to Chris Hentz, Vice President of STE San Antonio Aerospace, UPS mechanics were only instructed to check for corrosion, not for signs of bearing failure. However, both Hentz and UPS pointed out that even as Boeing recommended "changes to the inspection requirement of the spherical bearing were warranted," the manufacturer also stated in the same communication that existing inspection requirements were sufficient.
Hentz's letter stated that Boeing "said that while the MD-11 inspection intervals and requirements for an inspection of the aft bulkhead were sufficient, changes to the inspection requirements of the spherical bearing were warranted to ensure that the migration of the outer race would be reliably detected and identified during inspection."
UPS contended that despite Boeing developing an enhanced inspection procedure and adding it to the MD-11 maintenance manual, the manufacturer never incorporated this procedure into its federally approved maintenance schedule, which would have made it mandatory.
"Relying on Boeing’s representations that the issue was not safety-of-flight and that existing MPD inspections were sufficient, UPS determined that no additional changes to its maintenance program were necessary beyond what was already being performed," the package delivery company stated.
Extended Inspection Schedules and Past Incidents
At one point, Boeing successfully petitioned the FAA to extend the required inspection interval for these components from every 19,900 takeoff and landing cycles to 29,260 cycles. This change was intended to allow airlines to consolidate major maintenance tasks and reduce aircraft downtime.
This request for a schedule extension occurred even after Boeing received reports of seven bearing flaws before the aircraft reached their original inspection limits. In the years following the schedule relaxation, three more instances of such failures were identified prior to the crash.
The UPS plane that crashed had completed 21,043 cycles, meaning it should have undergone a thorough inspection under the original schedule. A previous crash involving a similar plane model, occurring decades earlier, was attributed to improper maintenance rather than this specific flaw.
FedEx and other operators of the MD-11 reported at least 10 other instances of failures involving these bearings or their supporting components before the UPS crash. However, it remains unclear what maintenance practices may have differed among these operators.
FedEx resumed flying its MD-11s in May after the FAA approved Boeing's safety assurance plan. Following the November crash, the engine mounts underwent close inspection, and going forward, the spherical bearings will be replaced every 4,000 takeoff and landing cycles. UPS subsequently decided to retire its entire fleet of MD-11s earlier than planned in the aftermath of the incident.