What happened
On May 15, 1971, during the regional gliding championship in Buttwil, a Ka-6 CR glider, registration HB-675, was involved in a takeoff accident during a tow operation. The flight began at 12:44 PM on runway 34. During the initial takeoff roll, the right wingtip touched the ground shortly after the wingman released the left wingtip. This contact caused the glider to veer toward the right.
Instead of applying left rudder to correct the direction, the pilot applied right rudder, followed by several more incorrect rudder inputs. As the aircraft reached the end of the runway at an altitude of approximately 10 to 15 meters, the glider had drifted significantly to the right of the tow plane. At this point, the tow rope disconnected from the glider. Following the release, the aircraft entered a steep right-hand turn, lost airspeed, and stalled over the right wing. The Ka-6 CR impacted the ground at 12:45 PM, approximately 60 meters to the right of the runway axis and 40 meters past the runway end. The impact resulted in the destruction of the aircraft and one minor injury to the pilot.
The investigation
The investigation examined the pilot's experience, the mechanical state of the aircraft, and the takeoff dynamics. The pilot held valid glider and private pilot licenses, with significant flight time on this specific aircraft type. No health issues were identified as contributing factors. The aircraft was found to be airworthy with no pre-existing technical defects.
A critical factor identified was the configuration of the tow rope attachment. The rope was connected to a center-of-gravity coupling located to the left of the fuselage centerline. This arrangement naturally created a yawing moment to the right during towing, requiring significant left rudder compensation during the takeoff roll.
Findings
- The primary cause of the accident was the pilot's loss of control over the glider during the takeoff roll.
- The pilot's decision-making regarding rudder inputs was incorrect, as he applied right rudder instead of left to counteract the rightward veer.
- The aircraft entered an overbanked right turn after the tow rope disconnected, leading to a stall and subsequent crash.