What happened
On 19 December 2016, a Cessna C5/25, registered YU-BST, was performing a ferry flight from Geneva to Sion. While executing an instrument guidance system approach to runway 25, the crew transitioned to visual flight rules after reporting visual meteorological conditions. As the aircraft passed the area near the Sion hospital, approximately 2 nautical miles from the runway threshold, both pilots spotted a red object on their right side. The crew identified the object as a drone featuring three propellers. Although the aircraft and the drone were on opposing tracks, the crew noted the proximity of the unmanned aircraft. No immediate evasive maneuvers were necessary as the lateral and horizontal separation was deemed sufficient at that moment. The flight continued without further incident, landing safely at 10:49 UTC.
The investigation
The investigation established that the encounter occurred within the Sion control zone (CTR). Based on the aircraft's approach angle, the drone was likely operating at an altitude between 200 and 250 meters above ground level. The investigation highlighted that the operation of a drone within this area violated existing Swiss regulations. According to the Federal Office of Civil Aviation (FOCA), the use of drones weighing between 0.5 and 30 kg is prohibited within 5 km of civilian or military runways. Additionally, operating such aircraft within a control zone at altitudes exceeding 150 meters is strictly forbidden. Because the operator of the drone could not be identified, investigators could not determine if the breach was due to a lack of awareness of the law.
Findings
- The encounter took place within a restricted no-fly zone.
- The unauthorized operation of a drone within the Sion CTR at an altitude exceeding 150 meters was the primary safety issue.
- The drone was observed at an altitude significantly higher than the legal limit for the area.
Safety action
Investigators noted that because drones are primarily detectable only through visual means rather than collision warning systems, the risk of mid-air collisions is increasing. The report emphasizes the urgent need for technical measures to enable the detection of unmanned aircraft by both pilots and air traffic controllers, specifically through enhanced detect-and-avoid capabilities.