What happened
On September 6, 2020, at approximately 15:33 local time, a towing operation was underway at the Greiz-Obergrochlitz airfield. A Scheibe SF 25 C motor glider was performing a series of glider climbs to refresh the pilot's towing rating. After releasing a PZL-Bielswko SZD-50-3 "Puchacz" glider at approximately 450 m AGL, the motor glider pilot proceeded to descend toward runway 23 to release the tow cable via a low pass.
Due to the presence of another aircraft on final approach for runway 05, the air traffic controller instructed the motor glider pilot to delay the approach. Following this delay, the pilot performed the cable release. To comply with noise abatement procedures, the motor glider pilot turned approximately 20 degrees to the right after the initial climb, placing the aircraft on a course toward the runway 05 approach path.
Simultaneously, the glider was executing turns in the northern pattern for runway 05. The pilot of the glider observed the motor glider approaching from the rear left at an angle of approximately 45 degrees. Despite attempting an evasive climb, the two aircraft collided. The impact caused minor damage to the upper right wing skin of the Scheibe SF 25 C and minor paint scrapes to the fuselage and nose gear of the PZL-Bielsko SZD-50-3 "Puchacz". There were no injuries to the occupants of either aircraft, and both were able to land safely on runway 05.
The investigation
The investigation examined the flight paths using GPS data from the glider's FLARM collision warning system, which confirmed the maneuvers described by the crews. Investigators reviewed the airfield's operational procedures, noting that the use of cable release on a runway opposite to the active direction was a relatively new and unfamiliar practice at the airfield following the installation of a new asphalt runway. The investigation also analyzed meteorological conditions, specifically the impact of sun glare, and reviewed radio communications, though no recordings of the traffic controller's instructions were available for review.
Findings
- The primary cause of the collision was the release of the tow cable on a runway opposite to the active runway direction.
- The motor glider pilot turned into the path of the approaching glider while attempting to comply with noise abatement procedures.
- Both pilots were significantly hindered by sun glare from the southwest, which made the motor glider difficult to see against the bright sky.
- There was insufficient communication between the pilots and the air traffic controller, preventing a complete shared mental model of the traffic situation.
- The motor glider was not equipped with a collision warning system, whereas the glider was.
- The recent implementation of the cable-release procedure was unfamiliar to the participants, increasing the risk of operational errors.