What happened
On May 12, 2017, at approximately 17:40 local time, a serious loss of separation occurred between a Cessna F 172N and a Cessna 172E approximately 0.5 nautical miles south of the Leutkirle-Unterzeil aerodrome traffic pattern. Both aircraft were operating under Visual Flight Rules (VFR). Radar data indicated that the aircraft reached a minimum horizontal distance of approximately 0.03 nautical miles and a vertical separation of roughly 125 feet.
The Cessna F 172N was conducting a flight test from Hohenems-Dornbirn, Austria, to Leutkirch-Unterzeil. The pilot in command noted that after receiving a position report from the second aircraft, they attempted to request altitude information via radio but received no response. To maintain separation, the pilot instructed the trainee pilot to reduce speed to 60 knots. During the downwind leg, the tower controller alerted the crew to another aircraft positioned directly above them. The pilot reported seeing a landing gear wheel just above the front window and performed an aggressive control input to turn right, narrowly avoiding a collision. The pilot noted that the high-wing design of the aircraft prevented a view of the traffic from above.
Simultaneously, the Cessna 172E was conducting a training flight for an upcoming competition. The pilot had reported intentions to land at Leutkirch-Unterzeil and was executing a right-hand pattern. While performing a full circuit, the pilot reduced speed to 70 knots. A passenger in the rear seat eventually spotted the other aircraft approximately 20 meters below and 50 meters to the left of their position. Neither the pilot nor the front passenger had visual contact with the Cessna F 172N prior to the near-miss.
The investigation
The BFU investigation utilized radar data provided by the Bundeswehr to establish the precise flight paths and separation distances. The investigation examined radio communications on the Leutkirch Info frequency, though no recordings of the transmissions were available. The investigation also reviewed the flight profiles, weather conditions (which were CAVOK at the time), and the specific visibility limitations caused by the aircraft configurations.