What happened
On September 10, 2020, a Champion 8KCAB, registration OY-LUN, was conducting a local VFR instructional flight originating from Roskilde (EKRK). During the flight, the flight instructor and student pilot were performing upset recovery training within the Roskilde Terminal Control Area.
During the maneuvers, the crew experienced a significant restriction in flight control movement. Specifically, the ability to move the control stick to the right was limited, preventing the necessary aileron deflection required for right-hand turns. Due to this interference, the training session was immediately discontinued, and the aircraft returned to Roskilde without further incident. No injuries were reported, and no damage was sustained by the aircraft.
The investigation
The Danish Accident Investigation Board conducted a technical examination of the aircraft's control systems. Investigators discovered a ballpoint pen lodged within the right-hand no. 6 aileron sector. This pen did not belong to the crew, and the operator could not account for its presence in the aircraft.
An inspection of the cockpit and fuselage revealed that several unprotected openings existed, including gaps between the front rudder pedals and the cabin sidewalls, as well as an opening between the left sidewall and the aft lateral panel. These gaps provided a pathway for small objects to migrate from the cockpit into the aircraft belly. While the manufacturer had previously issued Service Letters (435 and 436) to address such risks through inspections and floorboard modifications, the modifications suggested in Service Letter 436 had not been implemented on OY-LUN.
Findings
- The ballpoint pen likely fell from the cockpit during a previous flight, entering the aircraft belly through unprotected floorboard openings.
- During the high-G maneuvers associated with upset recovery training, the pen shifted from the tail compartment into the aileron bellcrank mechanism.
- The pen became stuck in the aileron bellcrank, physically obstructing the movement of the control surfaces.
- The aircraft's floorboard configuration lacked the necessary extensions or revised panels recommended by the manufacturer to prevent loose items from reaching the control linkages.