What happened
On September 5, 2015, a SZD-59 Jantar Acro glider, operated by Aeroklub Częstochowski with registration SP-3765, was conducting aerobatic training flights at the Rudniki aerodrome. Following the completion of an aerobatic sequence, the pilot entered the landing pattern. During the fourth turn, the pilot deployed the airbrakes and subsequently closed them. Approximately 10 seconds after leveling out on the final straight, the pilot deployed the airbrakes again but found it impossible to close them despite multiple attempts.
Due to the combination of a very flat approach angle, strong headwinds, and the extended airbrakes, the glider touched down prematurely on an unmaintained area of the airfield characterized by tall grass, rather than the designated grass runway. In an attempt to stop the aircraft more quickly during the landing roll, the pilot deployed the full airbrakes.
The investigation
The investigation utilized video footage recorded by a camera mounted on the glider's tail, which allowed for a detailed analysis of the flight sequence. Investigators examined the airbrake mechanism on the ground following the incident. While the inspection found no mechanical difficulties in opening or closing the brakes, the video analysis revealed that the airbrakes were deploying asymmetrically. The investigation also considered the pilot's physical ability to manipulate the controls under the specific flight conditions.
Findings
- The primary cause of the incident was a too-flat approach profile and the premature deployment of the airbrakes, particularly given the presence of strong headwind.
- The fourth turn was executed too far out, leading to the shallow approach angle.
- The pilot failed to divert the flight path to the concrete runway (DS 260) when it became apparent that the glider would not reach the usable part of the airfield.
- The deployment of full airbrakes during the landing roll on tall grass was identified as a risk factor that could have caused a wing to drag and induced a ground loop or damaged the lower airbrake panels.
- The inability to close the airbrakes may have been attributed to insufficient physical strength by the pilot to overcome the mechanism's resistance during that specific maneuver.