What happened
On September 13, 2020, at Grenchen Airport, a series of dangerous airspace incursions occurred involving a helicopter, a jump plane, and parachutists. During a period of high traffic complexity caused by an electric aircraft fly-in, an Airbus Helicopters AS350 B3, registration HB-ZNL, was cleared for departure. The air traffic controller (ATC) authorized a left turn that directed the helicopter through the 'Parabox'—a reserved airspace for parachutists. At the time, several parachutists were still descending, and the helicopter passed just 30 to 40 meters above them.
Simultaneously, a second conflict developed between the departing helicopter and a Pacific Aerospace 750XL, registration HB-TCP, which was on final approach after dropping jumpers. The two aircraft crossed paths on opposing headings at approximately 2,300 feet AMSL. The horizontal separation dropped to 0.4 NM, with 0 ft of vertical separation. Neither pilot reported seeing the other aircraft during the encounter.
The investigation
An investigation by the SUST revealed that the incident was not reported to the board immediately, only coming to light months later. The investigation examined the coordination between the parachute jump leader and the ATC, the visibility from the control tower, and the operational pressures present during the 'Electrifly-In' event. The inquiry also reviewed the communication protocols for aircraft dropping jumpers, noting that pilots become unavailable on the tower frequency during the drop phase.
Findings
Several critical factors contributed to the near-collisions:
- The air traffic controller forgot that the Parabox was active and that parachutists were still in the air when issuing the departure clearance.
- There was a complete lack of communication between the parachute jump leader and the air traffic controller.
- The control tower lacked a dedicated status indicator for the Parabox, and the controller had no direct visibility of the parachutists' landing zone.
- High workload and complexity were driven by the simultaneous presence of numerous electric aircraft and the lack of a prior briefing for the fly-in event.
- The jump plane (HB-TCP) remained off the tower frequency for an extended period during the jump sequence, making integration into the circuit difficult for the controller.
Safety action
Following the incident, Skyguide implemented a standardized procedure on September 22, 2021. This includes a visual reminder system to signal when the Parabox is active, intended to improve situational awareness for controllers, particularly during shift handovers or training.