What happened
On February 12, 2015, a serious near-collision occurred approximately 4 nautical miles southeast of Meiringen Airfield (LSMM). The incident involved a Northrop F-5E Tiger II operated by the Swiss Air Force, flying under the callsign Tractr2, and an Airbus Helicopters AS 350 B3, registration HB-ZNH, operated by Swiss Helicopter AG.
The sequence began when the pilot of the fighter jet requested a flight plan to a shooting zone via Axalp. Shortly after, the pilot of the AS 350 B3 requested a descent via Rosenlaui. Air traffic control cleared the helicopter to descend to 8,000 ft QNH. Following the takeoff of the F-5E Tiger II from runway 28, the controller restricted the fighter's climb to 7,000 ft QHD to maintain separation from the descending helicopter. The controller then cleared the helicopter to continue its descent, provided the pilot maintained visual contact with the fighter. Approximately 30 seconds later, the two aircraft crossed paths at an altitude of roughly 6,800 ft MSL, with a horizontal separation of only about 40 meters and a vertical separation of less than 100 meters.
The investigation
The SUST investigation focused on the flight paths, air traffic control instructions, and the technical capabilities of both aircraft. The inquiry examined radar data, flight recorder information from the helicopter, and the specific instructions provided by the Meiringen aerodrome controller. The investigation also reviewed the use of conditional clearances and the equipment standards for state-operated aircraft operating in civilian airspace.
Findings
- The primary cause of the near-collision was that the AS 350 B3 pilot did not adhere to the assigned altitude during the descent.
- A systemic contributing factor was that the F-5E Tiger II was not equipped with a collision warning system, which limited the crew's ability to detect the approaching helicopter.
- The investigation identified that the air traffic controller's use of a conditional clearance introduced a margin for interpretation that posed a safety risk, even though it did not directly trigger this specific event.