What happened
On October 2, 2018, an Agusta Westland AW10CO9SP helicopter, registration HB-ZRP, departed from the Rega base in Interlaken for a training flight. As the aircraft climbed westward toward Lake Thun, the pilot monitored the Meiringen military airfield frequency and became aware of three Boeing F/A-18 Hornet fighter jets departing from Meiringen and flying toward Interlaken.
During the flight, the fighter jet formation adjusted its path to avoid paragliders and other aircraft. The flight leader of the jets reported via radio that they had identified two other aircraft in the area and that there was no threat. However, the helicopter pilot only partially heard this transmission, perceiving only a vague traffic alert. While the pilot's collision warning system began issuing proximity and traffic alerts, the pilot initiated a descent to avoid the approaching jets. At the point of closest approach, the aircraft were separated by approximately 100 meters horizontally and 50 meters vertically.
The investigation
The investigation focused on why the fighter jet pilots did not detect the helicopter earlier. While the helicopter was equipped with a collision warning system (TAS 5 and Floice 6) that successfully alerted the pilot to the approaching threat, the military aircraft were not equipped with compatible collision warning technology. Consequently, the fighter jet pilots only spotted the helicopter at the last moment, necessitating an immediate climb to avoid a collision.
Findings
- The helicopter pilot's ability to perform an evasive maneuver was aided by the active collision warning system on the HB-ZRP.
- The fighter jet pilots did not detect the helicopter until the very end of the encounter because their aircraft lacked compatible collision warning equipment.
- The incident occurred in Class E airspace, where pilots are responsible for maintaining separation through the "see and avoid" principle.
Safety action
This incident mirrors a similar airprox that occurred in February 2018. The SUST has previously issued safety recommendation No. 474, which advocates for equipping military aircraft with collision warning systems that are compatible with civilian standards to prevent such close encounters.