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Credit: NTSB
A Cargojet Airways Boeing 767-300ER suffered "substantial" elevator surface damage when its auxiliary power unit (APU) doors—apparently not fully latched following routine maintenance—broke away in flight and struck the aircraft, an NTSB investigation found.
The June 17, 2024, incident occurred as the 767 was climbing through 13,000 ft. shortly after departing Cincinnati/Northern Kentucky International Airport (CVG) en route to Vancouver International Airport. Following a routine takeoff roll and start of climb, the two-pilot crew reported a "loud bang," airframe vibrations and multiple fault messages, said an NTSB final report released Aug. 20.
The aircraft was handling "normally," but the vibration intensity steadily increased, the report said. The pilots opted to return to CVG and made an uneventful landing.
A post-flight inspection found both APU doors were missing. Parts of one door—the left-hand panel—were recovered. Investigators found no signs of failure on the door latch components.
Flight data recorder data suggested the APU door began to separate when the aircraft was passing through 12,000 ft. "A review of the data also revealed no further anomalies that were related to the occurrence," the report said.
A review of company maintenance records showed the 767 underwent two separate routine inspections June 15-17. Both required opening the access doors.
"The maintenance technician who conducted the pre-departure check for the accident flight stated that he visually observed the APU doors and that they appeared to be latched and secured," the report said.
Following the incident, Cargojet inspected its fleet of 17 757s and 24 767s for APU access door anomalies. It found six aircraft that needed latch assembly adjustments "to bring them within minimum and maximum closure force limits," the NTSB said.
While conducting the work, Cargojet said it attempted to "simulate vibration and external forces to pull open" doors that needed adjustments. "They were unable to duplicate a failure and open the doors when an out-of-limit latch was correctly closed," the report said.
NTSB's inability to examine the missing door pieces prevented it from determining a probable cause. However, "it is likely that one or more latches were not fully engaged and closed before departure," the report said.
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