What happened
On April 29, 2013, at approximately 13:30 UTC, an AS-K13 glider, registration OK-6066, was performing a winch launch at Havlíčkův Brod airport (LKHB). The flight was being conducted by an instructor and a student pilot.
During the transition phase of the launch, the instructor noted a slight decrease in airspeed. In an attempt to manage the speed, the instructor reduced the angle of attack. However, the aircraft lost sufficient momentum and pitched nose-down into a steep descent at an altitude of approximately 10 meters. Despite the instructor's attempt to pull back on the control column to recover, the low altitude prevented the recovery of the flight path. The glider struck the ground nose-first, subsequently impacting with its skid, and came to a stop approximately 180 meters from the takeoff point. There were no injuries to the crew.
The investigation
The ÚZPLN investigation examined the actions of the crew, the winch operator, and the mechanical state of the aircraft. The winch operator reported that after the glider reached takeoff speed, he slightly reduced engine power, which decreased the tension on the towline. A witness at the airfield observed the towline slackening and subsequently slipping out of the glider's release mechanism. The investigation also reviewed the maintenance history of the AS-K13, noting that its annual inspection had been completed just two days prior to the accident.
Findings
- The instructor's reaction to the decreasing airspeed was insufficient to prevent the loss of flight energy.
- The reduction in engine power by the winch operator decreased the tension on the towline.
- The slackening of the towline caused it to slip out of the release hook.
- The loss of airspeed immediately following the release of the towline was the primary factor leading to the nose-down pitch.
- The altitude of approximately 10 meters was insufficient to recover from the steep descent.