What happened
On July 18, 2020, a Cessna 182T, registration HB-TER, was conducting an instrument flight rules (IFR) training mission from Speck-Fehraltorf to Grenchen. The flight crew was performing a missed approach procedure on runway 24. Simultaneously, a Pacific Aerospace 750XL, registration HB-TCP, was operating in the area to drop 13 skydivers. The skydiving aircraft was descending through 7,000 feet on a base leg for runway 06.
Due to heavy radio traffic, the pilot of the HB-TCP did not transmit a position report. Consequently, the air traffic controller (ATC) failed to provide traffic information to either aircraft. The two planes converged closely, reaching a minimum horizontal separation of only 0.1 NM and a vertical separation of approximately 100 ft. Both pilots were alerted to the danger by onboard collision warning systems, including PowerFlarm and TAS, and successfully performed evasive maneuvers.
The investigation
The investigation examined the coordination between Bern Approach and Grenchen Tower, specifically during a shift change between controllers. It was noted that the incoming controller had been instructed to manage the HB-TER via a visual missed approach due to the active "Parabox"—a localized airspace used to protect skydivers. The investigation also reviewed the impact of high traffic density, including glider activity and skydiving operations, on the controller's situational awareness.
Findings
- The primary cause of the near-collision was that the air traffic controller forgot the incoming aircraft, leading to a failure to issue necessary traffic alerts.
- The high volume of traffic on the frequency prevented the pilot of the HB-TCP from reporting their position.
- The activation of the "Parabox" airspace is not graphically displayed in the tower, requiring the controller to maintain this information mentally.
- The simultaneous presence of skydiving and glider operations created a high-workload environment with very low error tolerance.
- Onboard collision warning systems acted as a critical safety net, allowing both crews to avoid the collision.
Safety action
To assist with the management of the "Parabox" airspace and reduce the mental workload on controllers, Skyguide implemented a standardized procedure on September 22, 2021. This procedure provides a visual reminder of the active airspace to improve situational awareness, particularly during shift handovers and training sessions.