Near-collision of two light aircraft near Sursee avoided by last-second maneuver

Casualties unknown • Sursee, LU, CH

A high-risk encounter between a Cessna F172P and a Gyroflug SC 01 Speed Canard resulted in a horizontal separation of only 0.1 NM.

What happened

On the afternoon of November 24, 2018, two light aircraft experienced a dangerous close encounter near Sursee, Switzerland. The first aircraft, a Reims Cessna F172P with registration HB-CIO, was performing a flight between Buttwil and Langenthal. At approximately 4,000 ft AMSL, the pilot of the HB-CIO noticed an aircraft approaching from the right wing and performing a sharp left turn. The pilot estimated the lateral distance to the other aircraft was only about 50 meters.

The second aircraft, a Gyroflug SC 01 Speed Canard registered as HB-UCT, was returning from a flight originating in Birrfeld. The pilot of the HB-UCT spotted the Cessna approximately 300 meters away and immediately initiated a left-hand evasive maneuver, crossing behind the path of the HB-CIO. The encounter was characterized by a vertical separation of 0 ft and a horizontal separation of just 0.1 NM.

The investigation

An investigation by the SUST established that both aircraft were operating under Visual Flight Rules (VFR) in good weather conditions. Radar data confirmed the extreme proximity of the two aircraft during the encounter.

The investigation examined the cockpit equipment of both vessels. The HB-CIO was equipped with a Mode-S transponder and a PowerFlarm collision warning system, though the pilot was reportedly unaware that the warning system was active. The HB-UCT was equipped with a Mode-S transponder but lacked any collision avoidance or traffic information system.

Findings

Several factors contributed to the near-collision:

  • The aircraft were approaching each other at a constant angle of approximately 120 degrees, creating a "standing bearing" effect that makes detecting converging traffic significantly more difficult.
  • Visual detection was severely hindered by aircraft design and cockpit geometry; the pilot of the HB-CIO had a restricted view to the right due to the cabin structure and a passenger, while the pilot of the HB-UCT had their forward view partially obstructed by the aircraft's elevator.
  • While the PowerFlarm on the HB-CIO was likely operational and capable of receiving the HB-UCT's transponder signal, the lack of compatible, interoperable warning systems between the two aircraft meant the pilot did not receive an effective alert.
  • The encounter was only resolved due to the rapid, instinctive evasive action taken by the pilot of the HB-UCT.

Probable cause

The near-collision was caused by the difficulty of detecting converging traffic due to a 'standing bearing' approach, compounded by obstructed cockpit visibility and the lack of interoperable collision avoidance technology between the two aircraft.

Frequently asked questions

What happened in the 2018-11-24 REIMS AVIATION S.A. F172P accident near Sursee, LU, CH?

A high-risk encounter between a Cessna F172P and a Gyroflug SC 01 Speed Canard resulted in a horizontal separation of only 0.1 NM.

What aircraft was involved and where did it happen?

The accident on 2018-11-24 involved a REIMS AVIATION S.A. F172P, registration HB-CIO, at Sursee, LU, CH.

What was the probable cause of the accident?

The near-collision was caused by the difficulty of detecting converging traffic due to a 'standing bearing' approach, compounded by obstructed cockpit visibility and the lack of interoperable collision avoidance technology between the two aircraft.

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