What happened
On March 18, 2021, a training flight involving a Robinson R44 II helicopter, registration HB-ZWJ, encountered two Swiss Air Force F-5E Tiger II fighter jets (registrations J-3/044 and J-3094) during a dangerous close proximity event. The helicopter was conducting a training flight from Bern, carrying a flight instructor, a student, and two passengers, traveling through the Bernese Oberland.
At approximately 16:41, the two fighter jets, returning from an air combat exercise near Payerne, descended below the cloud layer to fly at a lower altitude. While the pilots had coordinated with the tactical control center, the center had confirmed no other traffic was visible on radar at that time. However, as the jets descended, the control center lost radar contact with them. At 16:43, near Thun, the two fighter jets crossed the flight path of the HB-ZWJ at a ground speed of approximately 470 knots. The helicopter pilot only spotted the jets immediately before the crossing, estimating they were passing only 30 to 50 meters above the helicopter's altitude.
The investigation
The SUST investigation utilized data from the Air Force and Skyguide radar, as well as the helicopter's Spidertracks 5 monitoring system. The investigation established that the helicopter was not visible to the military's radar system due to the local topography and its flight altitude. Consequently, the tactical control center could not provide any traffic advisories to the fighter pilots. Furthermore, the investigation found that the fighter pilots had no visual or radar contact with the helicopter prior to the encounter, and the pilots were operating at their maximum visual scanning capacity.
Findings
- The primary cause of the near-collision was that the fighter jet crews did not visually identify the helicopter and lacked technical assistance to do so.
- The lack of compatible collision warning systems on all three aircraft meant there was no safety net to alert the crews to the proximity of the other aircraft.
- The high speed of the F-5E Tiger II jets (470 knots) meant that an effective evasive maneuver would have required detection at least 12.5 seconds in advance, covering a distance of nearly 3,000 meters, which was not possible in this instance.
- The helicopter was invisible to the military radar due to terrain masking and altitude.
- The incident represents a recurring safety deficit, as similar lack of equipment was noted in previous investigations involving military and civil aircraft.