What happened
On August 5, 2005, a Schempp-Hirth Ventus C glider, registration D-1750, was conducting a local flight near the Mont Dauphin aerodrome. Approximately 35 minutes into the flight, the pilot heard a loud snapping sound originating from the rear of the cockpit. Immediately following this sound, the left airbrake deployed and became stuck in the extended position, and the left aileron became unresponsive. While the right airbrake remained retracted, the pilot struggled to maintain a stable flight path. Due to the difficulty in controlling the aircraft's trajectory, the pilot opted to perform an emergency landing in a field located approximately three kilometers from the runway threshold. The pilot neglected to extend the landing gear prior to impact, but the aircraft sustained only minor damage.
The investigation
The investigation focused on the mechanical failure of the left wing's automatic control connections. Examination of the aircraft revealed that the funnels used for the automatic connection of the wing controls had shifted inward toward the fuselage. This movement resulted in a loss of continuity between the control cables and the wing surfaces. Specifically, the composite carbon fiber fabric that secures the pivot axis for these funnels had torn and detached from the fuselage.
Investigators analyzed the design of the control linkage support, noting that a void exists between the upper part of the funnel axis and the fuselage. This design creates a significant stress concentration zone. Evidence of high mechanical loads was found on the funnels and the airframe near the automatic connection points, indicating that excessive force had been applied to the axis.
Findings
- The primary cause of the failure was the improper following of wing assembly procedures during the attachment of the wings.
- The design of the control linkage support was inadequate, as the empty space near the pivot axis created a point of high stress concentration.
- The structural failure was triggered by excessive forces exerted on the axis during assembly or disassembly operations.