Near-collision of IFR and VFR aircraft in Sion TMA

Casualties unknown • Sion, VS, CH

A dangerous convergence between a Piper PA-34 and a Beechcraft A23-24 in Swiss airspace resulted in a separation of less than 0.2 NM.

What happened

On 22 February 2012, a serious air proximity incident occurred within the Sion terminal area (TMA) in Switzerland. A Piper PA-34 – 200T, operating under instrument flight rules (IFR) on final approach to runway 25, intersected the path of a Beechcraft A2 .23-24 flying under visual flight rules (VFR). The Beechcraft was traversing the Rhone valley in a northerly direction when the two aircraft converged. At the point of minimum separation, the aircraft were only approximately 50 feet apart vertically and less than 0.2 NM apart horizontally.

The investigation

The Swiss Accident Investigation Board (SAIB) examined the flight trajectories, radar data, and air traffic control communications. The investigation established that the air traffic controller provided traffic information to both aircraft regarding their convergence. The crew of the HB-LMM (the Piper) observed the HB-ENV (the Beechcraft) and immediately executed a left-hand avoidance maneuver to pass behind the conflicting aircraft.

Investigators also reviewed the technical capabilities of the Sion control tower, noting that the workstations were not equipped with a short-term conflict alert (STCA) system. Additionally, neither aircraft was equipped with a Traffic Collision Avoidance System (TCAS) or Traffic Advisory System (TAS). The investigation also looked into the controller's radar console, which was described as having inaccurate "jumps" in the radar plots.

Findings

The incident was driven by the dangerous convergence of IFR and VFR traffic within the same airspace under visual meteorological conditions.
The Sion VFR regional chart lacked specific VFR routes or designated exit points that would have ensured geographical separation between VFR and IFR traffic.
The air traffic controller provided implicit instructions to the VFR pilot that did not sufficiently account for the pilot's intention to cross the valley.
There was an absence of established procedures in the Swiss VFR manual regarding specific routing or clearance requests for VFR aircraft crossing the TMA from Sion.

Probable cause

The incident was caused by the convergence of two aircraft operating under different flight rules (IFR and VFR) in the Sion TMA, exacerbated by a lack of designated VFR routes or exit points to maintain separation from IFR traffic.

Frequently asked questions

What happened in the 2012-02-22 BEECH AIRCRAFT CORPORATION A23-24 accident near Sion, VS, CH?

A dangerous convergence between a Piper PA-34 and a Beechcraft A23-24 in Swiss airspace resulted in a separation of less than 0.2 NM.

What aircraft was involved and where did it happen?

The accident on 2012-02-22 involved a BEECH AIRCRAFT CORPORATION A23-24, registration HB-ENV, at Sion, VS, CH.

What was the probable cause of the accident?

The incident was caused by the convergence of two aircraft operating under different flight rules (IFR and VFR) in the Sion TMA, exacerbated by a lack of designated VFR routes or exit points to maintain separation from IFR traffic.

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