What happened
The accident involved a McDonnell Douglas DC-10 aircraft during cruise flight. At flight level 170, the forward one-third section of the port-side core cowl door on the No. 3 engine detached from the engine assembly while the aircraft was airborne. The separated component first impacted the leading edge of the right wing before continuing its trajectory to puncture the main fuselage structure. This sequence of impacts resulted in immediate and rapid decompression of the cabin environment.
The investigation
Examination of the maintenance records and service bulletins revealed critical discrepancies in the installation procedures for the engine cowl door. Specifically, the core cowl door latches had not been adjusted according to required specifications. Furthermore, the core cowl door shear pins were missing from their designated locations. These omissions directly contradicted the requirements outlined in McDonnell Douglas Service Bulletin No. 71-86, which was dated May 12, 1985.
Findings
The primary factor contributing to the incident was the failure to adhere to manufacturer service instructions. The lack of proper latch adjustment and the absence of shear pins allowed the cowl door to become unsecured during flight operations. This mechanical oversight led directly to the structural separation of the component, the subsequent damage to the wing and fuselage, and the loss of cabin pressure.
Safety message
Strict compliance with manufacturer service bulletins is essential for maintaining airframe integrity. Maintenance crews must ensure that all latches are correctly adjusted and that required shear pins are installed in accordance with specific service documentation to prevent in-flight component separation.