What happened
On April 9, 2012, a Schleicher K 7 glider, registration OK-1628, was performing a winch launch at Polička airport. The flight was part of a training session following the winter break, with a pilot undergoing type-specific renewal and an instructor acting as the second pilot.
During the transition to the climb phase, approximately 15 meters above the ground, the aircraft's airspeed dropped below 80 km/h. This loss of airspeed was caused by a gradual reduction in power from the H-4 Hercules winch engine. In response to the deteriorating situation, the crew disconnected the winch cable and attempted to push the glider below the horizon to manage the energy. However, the glider could not maintain sufficient altitude, resulting in a heavy landing on the main landing gear. The aircraft slid for approximately 90 meters along the grass runway.
While the crew members escaped the cabin without injury, the impact caused significant structural damage to the glider, including a deformed fuselage frame, a torn fabric covering, and damage to the main landing gear attachment.
The investigation
The ÚZPLN investigation focused on the mechanical state of both the glider and the winch, as well as the crew's performance. The investigation established that the glider was in a proper state of maintenance and no technical defects were found within the aircraft itself. Regarding the winch, investigators found that the engine could not be restarted initially, but after bleeding the fuel system, it returned to normal operating parameters. The investigation also noted that the winch engine's power loss was caused by air entering the fuel system.
Findings
- The primary cause of the accident was the delayed reaction of the instructor pilot to the loss of winch tension during the critical climb phase.
- The winch engine experienced a loss of power due to air entering the fuel system.
- The pilot flying had limited recent experience on this specific glider type following the winter break.
- The instructor's concentration may have been compromised due to the high number of winch launches performed earlier that day.