What happened
The left cargo door separated from the aircraft during flight operations. The component was identified as a Hamilton cargo door, which had been installed under a Supplemental Type Certificate (STC). The specific STC requirements mandated the installation of three hinges on the top edge and three pins on the bottom edge, along with an overcenter locking mechanism on the handle to secure the pins.
The investigation
Post-accident examination revealed significant discrepancies between the installed hardware and the STC specifications. Only two hinges were found installed on the door, falling short of the required three. Furthermore, only two of the bottom pins were operational. Crucially, there was no operable overcenter locking mechanism present on the handle, which is essential for securing the door in the closed position.
Findings
The separation of the cargo door was directly linked to the failure to comply with the STC installation requirements. The inadequate number of hinges and pins compromised the structural integrity of the attachment points. Additionally, the absence of a functional overcenter locking mechanism meant the door could not be securely latched, allowing it to detach during flight.
Safety message
This incident highlights the critical importance of adhering strictly to Supplemental Type Certificate (STC) installation requirements when modifying aircraft components. Proper hardware count and functional locking mechanisms are essential for maintaining airworthiness and preventing in-flight separation of doors or panels.