What happened
On August 23, 1964, a glider from the Churfirsten Gliding Group was performing a winch-assisted takeoff at a military airfield under favorable weather conditions. During the ascent, at an altitude between 50 and 80 meters, the steel winch cable snapped. The pilot immediately released the remaining cable fragment and stabilized the Austria Standard HB-718 into a normal glide.
In an attempt to return toward the takeoff site, the pilot initiated a tight left-hand turn at a very low altitude. During this maneuver, the aircraft's airspeed dropped below the stall threshold, causing the glider to wing over and enter a spin. The aircraft struck the ground approximately 300 meters from the takeoff point, resulting in the death of the pilot and the total destruction of the aircraft.
The investigation
Investigators examined the condition of the winch cable, which was a 1300-meter steel rope with a 4.8 mm thickness. The inspection revealed that the cable was heavily used and contained 20 previous repair points. Rather than using traditional splicing, these repairs had been made using lightweight metal sleeves (Talurit clamps).
The investigation also reviewed the pilot's flight history, noting that while he had significant flight experience, he had relatively limited hours specifically on this high-performance model. Additionally, the commission reviewed local operating procedures, which recommended that turning maneuvers following a failed winch takeoff should only be initiated at altitudes of at least 150 meters.
Findings
- The primary cause of the accident was the pilot initiating a turning maneuver at an insufficient altitude following the cable break, which led to a stall.
- The winch cable failed at a previously repaired section. The metal sleeves used for the repair had been significantly worn down by abrasion against the paved runway, which compromised the integrity of the connection.
- The pilot's decision to attempt a return to the takeoff site increased the risk, as the low altitude left no margin for error once the stall occurred.
- Contributing factors included the difficulty of maintaining precise control during the transition from headwind to tailwind at low altitude and the pilot's limited experience with this specific aircraft type.