What happened
On June 15, 2015, a private pilot was conducting a cross-country flight in an LS 6b sailplane, registration OH-765, departing from Uppsala/Sundbro airport. After approximately two and a regular half hours of flight, the thermal activity began to subside. While flying at an altitude of 300 meters, the pilot decided to perform an out-landing in a nearby field measuring approximately 350 meters in length.
During the approach, the pilot continued to search for thermals between 300 and 200 meters, leading to several unsuccessful landing attempts. Flight data indicates the final approach was flown abnormally; the downwind leg was at a low altitude, and the base leg was positioned very close to the start of the field. The final approach path ended over a tall tree line.
During the landing process, the pilot encountered difficulty deploying the airbrakes. The pilot only realized that the airbrake lever required a specific lateral movement—pulling the lever to the right—before it could be pulled backward. Because of this delay, the aircraft's braking performance was limited, as the flaps were only set to +10 degrees instead of the standard +15 degrees.
The aircraft overshot the landing area. In an attempt to stop before reaching the far end of the field, the pilot executed a maneuver that resulted in a ground loop. During this rotation, the right wing struck the ground, causing the aircraft to spin 180 degrees and resulting in the aft fuselage breaking off. The pilot was uninjured and able to exit the aircraft independently.
The investigation
The investigation examined the flight path recorded by logger data, the mechanical operation of the airbrake lever, and the pilot's experience with the aircraft type. Investigators analyzed the design of the airbrake guide, noting that the specific mechanical path of the lever in this model requires a rightward movement before retraction/extension is possible. This design differs from later models of the LS 6 series, which feature a chamfered guide allowing for direct rearward movement.
Findings
- The approach was planned and executed in a highly questionable manner, with the base leg being too close to the field boundary.
- The pilot's limited experience with this specific aircraft model contributed to the late deployment of the airbrakes.
- The mechanical design of the airbrake lever guide necessitates a specific lateral movement that was not immediately recognized by the pilot.
- The effectiveness of the aircraft's braking was reduced because the flaps were only set to +10 degrees.