What happened
On August 10, 2023, a Cirrus SR20 and a Cessna 182P experienced a close approach in Class E airspace near Wuppertal, Germany. Both aircraft were operating under Visual Flight Rules (VFR). The SR20 was en route from Speyer/Ludwigshafen to Groningen, Netherlands, while the Cessna 182P was flying from Loemühle to Freiburg.
Radar data indicates the aircraft were on a direct collision course with a high closing speed of approximately 260 kt. The minimum separation reached was roughly 0.16 NM horizontally and 100 ft vertically. The pilot of the SR20, alerted by an onboard Avidyne SkyTrax600 traffic collision avoidance system, observed the oncoming high-wing aircraft and performed an evasive left turn. The pilot of the Cessna 182P did not perceive the encounter and was in contact with Langen Information at the time.
The investigation
The BFU investigation examined the actions of both pilots and the air traffic service provider. The investigation found that the pilot of the SR20 acted appropriately by following the warning from his onboard equipment. The pilot of the Cessna 182P was unable to detect the threat, likely due to solar glare and the lack of receiving traffic information from the flight information service.
Investigators also scrutinized the Langen Information service. The air traffic specialist was in the initial phase of his shift and experiencing high workload due to heavy traffic and the need to identify another aircraft. Crucially, the investigation found that the Short Term Conflict Alert (STCA) system failed to generate a warning because the system had been configured to suppress alerts between aircraft operating under VFR.