What happened
On October 2, 2023, at approximately 18:27 local time, a serious airspace disturbance occurred near Bochum, Germany, involving two aircraft operating under visual flight rules (VFR). The first aircraft, a Cessna F 172P, was performing a sightseeing flight originating from Dortmund. As the pilot initiated a 180-degree turn around the Bochum city center, a second aircraft, a Robin DR400/180R, appeared to the right and slightly above the Cessna. The pilot of the Cessna estimated the distance at approximately 50 meters at one point, noting that the second aircraft was already turning away in a 45-degree arc.
The pilot of the Robin DR400/180R, flying from Ithwiesen to Essen/Mülheim, reported detecting the Cessna on a head-on course roughly three seconds before the closest point of approach. To avoid a collision, the pilot of the Robin executed an abrupt left-hand evasive maneuver. Radar data confirmed that the minimum horizontal separation between the two aircraft was approximately 0.08 NM (148 m) at the same altitude. There were no injuries and no damage to either aircraft or third parties.
The investigation
The BFU investigation examined the flight paths, cockpit environments, and air traffic services. The investigation established that the pilot of the Cessna had scanned the airspace before the turn but did not identify the conflict. The passengers in the Cessna also noted they only noticed the other aircraft shortly before the encounter. In the Robin, the pilot noted that visibility was significantly hindered by the low position of the sun.
The investigation also reviewed the performance of onboard collision warning systems. The Cessna was equipped with a Skyecho 2 system, which only generated an alert after the other aircraft had already begun its turn. The Robin was equipped with a FLARM system, which failed to generate any warning during the encounter. Furthermore, the investigation looked into the role of the Flight Information Service (FIS) at Langen-Information, finding that no traffic information had been provided to either pilot.
Findings
Several contributing factors led to the near collision:
- Visual impairment due to the low sun angle affecting the pilot of the Robin.
- Lack of traffic information from the FIS, as the controller was preoccupied with processing multiple initial calls and entering new aircraft into the system.
- Inadequate collision warning performance, as the Cessna's system alerted too late and the Robin's FLARM system provided no alert.
- Controller workload, which prevented the timely detection of the approaching aircraft and the subsequent delivery of traffic advisories.
- Systemic limitations in the air traffic control software, where certain VFR codes may be suppressed to prevent visual overload, potentially masking conflicts.