What happened
On September 10, 2016, a mid-air collision occurred during the final approach at the Großrückerswalde airfield during an aviation event. The ultralight aircraft, a Flight Design CT SW, was conducting a local sightseeing flight. Simultaneously, an Alexander Schleicher ASK 21 glider was completing an aerobatic program.
The glider pilot had finished his maneuvers at approximately 350 m AGL and was flying in a reversed position toward the airfield pattern. As the glider entered its final approach, it was flying in a side-slip with the left wing low. At this moment, the CT SW was approaching at a much lower altitude. The vertical stabilizer of the ultralight struck the trailing edge of the glider's right wing.
The impact caused the ultralight to experience an immediate increase in angle of attack, leading to an aerodynamic stall. The aircraft pitched forward violently and entered an almost vertical descent into a nearby forest. The impact was so severe that the pilot was unable to deploy the aircraft's emergency recovery system. The CT SW was destroyed, and two fatalities occurred. The occupants of the glider remained uninjured, though the ASK 21 sustained minor damage.
The investigation
The BFU investigation examined flight data from the ultralight's GPS, video footage from witnesses, and the aircraft wreckage. The investigation established that the ultralight was flying at a very low altitude during its final approach, making it difficult for the flight controller to spot.
Investigators also reviewed the glider's configuration. The pilot was operating the ASK 21 from the rear seat, a position that significantly restricts forward visibility. While the flight controller attempted to intervene via radio by instructing the ultralight to turn right, the collision occurred despite the pilot's attempt to comply with the instruction.
Findings
- Lack of visual contact between the pilots of both aircraft during the final approach.
- Inadequate communication between the participating pilots and the flight controller during landing preparations.
- The ultralight's low-altitude approach made it difficult for the flight controller to detect the aircraft in a timely manner.
- Reduced visibility for the glider pilot due to the decision to fly from the rear seat of the aircraft.
- The ultralight's sudden stall and vertical descent were caused by the physical impact with the glider's wing.