What aircraft was involved and where did it happen?

The accident on 2013-03-22 involved a aircraft, registration D-IKSI, at Sion Aéroport LSGS, VS, CH.

What was the probable cause of the accident?

The incident was caused by the dangerous convergence of two aircraft due to an air traffic controller's failure to ensure the arrival pilot followed specific instructions, compounded by inadequate ATC tactics for managing conflicting flight rules in the area.

Airprox investigation reveals separation failure near Sion

A near-collision between a Piaggio P180 and a Cessna Citation Jet occurred near the VALOR waypoint due to improper ATC instructions and lack of coordination.

What happened

On March 22, 2013, at 10:24 UTC, a serious airprox incident occurred near the VALOR waypoint, approximately 16 nautical miles southwest of Sion. The event involved two aircraft flying in opposite directions: a Piaggio P180 Avanti II, registration D-IKSI, operating under instrument flight rules (IFR) departing from Sion, and a Cessna C525 Citation Jet, registration N600HS, operating under visual flight rules (VFR) arriving toward Sion.

The aircraft were operating under different air traffic control jurisdictions at the time of the encounter. The N600HS was in contact with Geneva ACC, while the D-IKSI was communicating with Sion Tower. During the descent of the N600HS, the pilot canceled the IFR flight plan to proceed under VFR. The aircraft eventually converged, reaching a minimum separation of 2.8 NM horizontally and 650 ft vertically. Neither crew established visual contact with the other, and no avoidance maneuvers were performed despite both aircraft being equipped with TCAS I.

The investigation

SUST examined radio communications and coordination records between Geneva ACC and Sion Tower. The investigation established that the N6 and D-IKSI were in different airspace classes during the encounter. The investigation also reviewed the technical performance of the Short Term Conflict Alert (STCA) system, which activated on the Geneva controller's screen during the event.

Findings

The primary cause was the dangerous approach of two aircraft flying in opposite directions following the failure to comply with an air traffic control instruction given to the pilot in the approach phase.
An inadequate air traffic control tactic contributed to the incident.
A lack of specific procedures at Sion airport regarding the management of IFR departures when VFR arrivals are present in the adjacent airspace contributed to the risk.
The controller in Geneva authorized the N600HS to descend through levels that placed it in conflict with the departing traffic.

Safety action

Following the incident, the Sion coordinator's workstation was updated to include radar imagery from Geneva. Additionally, a specific operational reminder was issued to all controllers regarding the management of IFR arrivals transitioning to VFR near the VALOR waypoint. The investigation also highlighted a safety deficit regarding the lack of defined procedures for managing simultaneous IFR departures and VFR arrivals in the complex airspace shared between Swiss and French jurisdictions.