Accident Details
On 25 May 2015, at approximately 19:16 local time, a glider of type SZD-9bis Bocian 1E, registration SP-3042, operated by Aeroklub Warszawski, was conducting a training flight at Warszawa-Babice airport (EPBC). The crew consisted of a glider instructor and a student pilot. The flight was part of basic glider training, specifically exercise I, exercise 5, variant A, which involved simulating a winch cable break at low altitude.
During the exercise, the winch operator cut the cable at low altitude as planned. The crew executed a correct transition to horizontal flight and turned to land straight ahead. After releasing the cable, the winch cable parachute suddenly inflated and lifted alongside the fuselage at aileron height, moving rearward onto the wing. The cable end (towing loop) wrapped around the right wing and became jammed in the aileron gap near the fuselage. The cable began to pull the glider off course, causing a gentle turn with sideslip. By this time, the winch operator had already cut the cable.
The glider descended and struck the ground while sideslipping, resulting in damage to the main landing gear (the wheel was forced into the fuselage behind the wheel well). The glider stopped on the concrete runway, east of its centerline. No other damage to the aircraft was found, and the crew sustained no injuries.
Probable Cause
According to the investigation, the accident resulted from three causes: 1. The crew's overly rapid reaction to the planned cable break at low altitude, specifically simultaneously releasing the cable while transitioning the glider to a glide, which caused the glider to "catch up" to the winch cable. 2. The small angle of the winch cable at the moment of release, which favored a situation where the emergency-released cable remained at glider altitude before beginning to descend. 3. The insufficient weight of the winch cable parachute surface due to the synthetic cable's significantly lower weight compared to steel cables, resulting in a slower descent than optimal.
Contributing factors may have included a sudden thermal gust that intensified the lift of the parachute and cable, and a too-short distance between the parachute and the glider's release hook, increasing the risk of the glider flying "under" the cable.
Safety Actions
The investigating entity (the operator's committee) recommended the following preventive measures:
- In training flights simulating a winch cable break at low altitude, a much later release of the winch cable from the glider should be applied.
- Steel towing loops of increased length (about 8 meters) were manufactured.
- During training of low-altitude emergency release procedures, it was recommended to tape the parachutes so they do not fully inflate and have an increased descent rate.
- Instructors were briefed on the incident.
The Polish State Commission for Aircraft Accident Investigation noted an increasing frequency of hazardous events related to winch starts and simulated emergencies. Discussions were held at briefings of Polish Aero Club training chiefs, and work was underway to develop training methodology for simulated winch cable breaks at low altitude.