What happened
On February 19, 2017, at 12:31 UTC, a serious incident occurred within the Sion Airport (LSGS) control zone involving two light aircraft. The first aircraft, a Cessna 172S with registration HB-CZO, was conducting a flight school training mission. It departed from Hausen (LSZN) and was en route to Sion. Simultaneously, a Piper PA-28R-201, registered as HB-PQY, was operating a private flight from Langenthal (LSPL) toward Sion. During the approach to the airfield, the two aircraft experienced a dangerous separation, resulting in a close encounter.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) opened an inquiry into the event on February 24, 2017. Investigators examined the circumstances surrounding the flight paths and the proximity of the two aircraft within the Sion control zone. The investigation focused on determining whether technical, organizational, or systemic failures contributed to the near-collision.
Findings
Upon review, the investigation determined that the serious incident was not caused by technical, organizational, or systemic factors. While certain risk-increasing factors were identified during the process, these specific elements had already been addressed and documented in a separate investigation. Consequently, the SUST concluded that further investigation into this specific occurrence would offer limited additional value to aviation safety prevention.