What happened
On June 26, 2016, at approximately 13:14 UTC, a serious near-collision occurred at Grenchen Airport (LSZG) involving a Piper PA-2-181 Archer II, registration HB-PPY, and two military parachutists from the Swiss Army. The aircraft was conducting a private training flight in the airport vicinity under Visual Flight Rules (VFR).
During the approach, the aerodrome control officer (ADCO) instructed the pilot of the HB-PPY to execute a go-around and proceed with an approach to the grass runway 07R. However, during the final stages of the approach, the pilot initiated a slight left turn toward the grass runway 07L. At that same moment, two parachutists were descending toward the threshold of runway 07L. The controller realized the error and ordered an immediate right turn. The aircraft passed the two parachutists at the same altitude with a horizontal separation of less than 40 meters, representing a high risk of collision.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined radio communications, radar data, and statements from the pilot, the parachutists, and the air traffic controller. The investigation focused on the flight path, the coordination of the parachute jump, and the controller's management of the airspace.
Findings
- The primary cause of the incident was that the pilot of the HB-PPY targeted the wrong runway due to a confusion during the final approach.
- A contributing factor was that the air traffic controller changed the original separation concept without providing the pilot with specific information regarding the approaching parachutists.
- The investigation identified a systemic risk in the simultaneous use of the airfield for both aircraft traffic and parachute jumping without clearly defined spatial or temporal separation.
- The pilot's mental model of the situation was incomplete, as they had not requested clarification regarding the specific landing zone for the parachutists, assuming they would land in the standard area north of the hangars.