Overview
On 13 September 2020, at 12:07 UTC, a serious incident involving an airprox occurred at Grenchen Airport (LSZG) in airspace Delta. The incident involved a Pacific Aerospace PAC 750XL (registration HB-TCP) and an Airbus Helicopters AS350 B3 (registration HB-ZNL), as well as parachutists. The Parabox, reserved for parachute operations north of the runway axis, was active at the time.
Aircraft Involved
- Aircraft 1: Pacific Aerospace PAC 750XL, registration HB-TCP, owned and operated by Verein Skydive Grenchen. The aircraft was operating under visual flight rules (VFR) in private mode, with a flight phase of approach. The pilot, a Swiss national born in 1957, held a Commercial Pilot Licence for aeroplanes (CPL(A)) issued by the Federal Office of Civil Aviation (BAZL) under EASA. He had 3400 total flight hours, with 450 hours on type.
- Aircraft 2: Airbus Helicopters AS350 B3, registration HB-ZNL, owned by Kunert Aircraft Asset GbR and operated by Mountain Flyers. It was operating under VFR in commercial mode, with a flight phase of start and climb. The pilot, a Swiss national born in 1964, held a Commercial Pilot Licence for helicopters (CPL(H)) issued by BAZL under EASA. He had 2115 total flight hours, with 46 hours on type.
Air Traffic Control
The air traffic controller on duty was a Swiss national born in 1969, holding an Air Traffic Controller Licence based on EU Directive 805/2011, issued by BAZL. Two controller positions were staffed: Aerodrome Controller (ADC) and Ground Control (GRO). Additionally, the event organizer of the Electrifly-In was present in the tower.
Incident Sequence
At approximately 12:06 UTC, the pilot of HB-ZNL requested takeoff clearance from the aerodrome controller with a left turn toward waypoint HW. The controller granted clearance, expecting that no parachutists remained in the Parabox, based on his experience that parachutists are usually on the ground before the drop aircraft returns. However, several parachutists were still in the Parabox, close to landing. The helicopter flew over them at an altitude of about 30 to 40 meters while heading west.
Meanwhile, HB-TCP, which had just dropped parachutists, was on a right base leg for runway 06 and turning onto final approach. Neither pilot received traffic information about the other aircraft from the tower. At 12:07 UTC, the two aircraft crossed at 2300 ft AMSL on opposite headings. The minimum horizontal distance was 0.4 NM, and vertical separation was 0 ft. Both pilots reported not seeing the other aircraft. HB-TCP landed uneventfully on runway 06, and HB-ZNL continued its flight without further incident.
Observations
The investigation noted several factors regarding parachute operations at Grenchen:
- The helicopter departure route passed directly through the Parabox.
- The controller had limited visibility of the Parabox from the tower and could not see the parachutists' landing area. He had to leave his position to visually check the box.
- No communication existed between the parachute jump service leader and the controller.
- No status display for the Parabox was available in the tower.
- The controller was solely responsible for determining whether parachutists were present in the Parabox.
According to the agreement for parachute operations within Grenchen CTR or RMZ, the drop pilot reports two minutes before jump readiness, after which he is not on the tower frequency until re-entering the CTR for landing. This prevented the controller from contacting the drop pilot during the incident.
The helicopter was not equipped with a collision warning device. Technical limitations were not a factor in this incident. A similar incident had occurred on 18 July 2020.