What happened
On August 3, 1997, a Grob G 109B motor glider departed from the Hütten-Hotzenwald glider airfield for a private sightseeing flight. At approximately 17:58 local time, the aircraft was flying west near the Schopfheim model airfield, where a "friendship flight" event was being held for various model flying clubs.
Simultaneously, a remote-controlled motor aircraft was performing a glider tow operation. At an altitude of approximately 150 to 200 meters, the pilot of the model glider released the tow rope. Shortly after this release, the eastbound-bound model aircraft collided with the right wing of the westbound-bound Grob G 109B.
The impact caused the outer section of the motor glider's right wing to break off. The incapacitated Grob G 10SB subsequently crashed into a wooded area, resulting in two fatalities for the pilot and passenger. The remote-controlled model aircraft also sustained heavy damage and crashed in a nearby forest.
The investigation
The BFU investigation examined the technical condition of both aircraft, the experience of the operators, and the environmental conditions. The motor glider pilot was an experienced pilot with 563 total flight hours. The controller of the remote-controlled model had approximately 20 years of experience in model flying.
Technical inspections revealed no mechanical failures in either the motor glider or the remote-controlled model's transmitter. The motor glider was properly maintained, and its weight and balance were within limits. Weather conditions were favorable, with clear skies and light winds, though the position of the sun was noted as a factor. The investigation also reviewed the flight sectors and altitude regulations for the model airfield, noting that while the collision likely occurred outside the designated model flight sector, the exact location could not be definitively established.
Findings
- The collision was caused by the failure of both operators to detect the other aircraft in time to perform an effective evasive maneuver.
- The controller of the remote-controlled model aircraft reported noticing the motor glider only a few meters away after the glider had already released from the tow.
- The motor glider pilot was likely blinded by the low position of the sun while flying westward, which prevented timely detection of the approaching model aircraft.
- While the investigation could not rule out that the motor glider was flying below the required minimum altitude for cross-country flight, or that the model aircraft had left its designated sector, these factors would not have prevented the accident had the aircraft been detected early enough.