Near-collision involving three aircraft near Zug

Casualties unknown • Steinhausen, ZG, CH

A Piper PA-34-200 narrowly avoided a collision with a glider tow formation during a flight over Switzerland.

What happened

On April 7, 2018, at approximately 14:37 local time, a near-collision occurred near the city of Zug, Switzerland. The incident involved three aircraft operating under Visual Flight Rules (VFR). The first aircraft, a Robin DR300-180R with registration D-EAIO, was acting as a tow plane, pulling an ASW 20 CL glider, registration HB-1784, on a flight departing from Hausen am Albis.

The tow formation was climbing steadily at a rate of approximately 3 m/s, following a path that turned south-southeast toward Rossberg. Simultaneously, a Piper PA-34-200, registration HB-LEM, was en route from Buochs to Zurich at a steady altitude of 4,700 ft AMSL.

As the tow formation passed near Baar, the glider pilot spotted the HB-LEM approaching rapidly from the front right. The glider pilot immediately alerted the tow pilot via radio. Despite attempts by both pilots to signal the oncoming aircraft through wing rocking, the pilot of the HB-LEM did not initiate an avoidance maneuver. While the tow pilot noted the HB-LEM would pass slightly high and behind the lead aircraft, the glider pilot—positioned roughly 60 meters behind the tow plane—realized the HB-LEM was on a direct path toward the glider. To mitigate the risk, the glider pilot briefly reduced the rate of climb. The HB-LEM crossed the flight path of the glider with a vertical separation of only about 20 meters.

The investigation

The investigation focused on why the pilot of the HB-LEM failed to recognize the tow formation despite seeing other aircraft in the area. It was noted that the HB-LEM was equipped with a FLARM collision warning system, as were both the tow plane and the glider. However, none of the three pilots reported receiving an audible or visual alert from their FLARM devices during the encounter. It could not be definitively determined if an alert was triggered in any of the aircraft.

Findings

  • The pilot of the HB-LEM and their passenger observed several other aircraft in the vicinity but failed to perceive the tow formation.
  • The minimum separation between the aircraft was approximately 20 meters.
  • The pilot of the HB-LEM did not initiate an avoidance maneuver despite being alerted by the glider pilot via radio.

Probable cause

The near-collision was caused by the failure of the pilot of the Piper PA-34-200 to recognize the presence of the glider tow formation, combined with the lack of effective visual signaling or recognized electronic collision warnings during the encounter.

Frequently asked questions

What happened in the 2018-04-07 ALEXANDER SCHLEICHER GMBH & CO. SEGELFLUGZEUGBAU ASW 20 CL accident near Steinhausen, ZG, CH?

A Piper PA-34-200 narrowly avoided a collision with a glider tow formation during a flight over Switzerland.

What aircraft was involved and where did it happen?

The accident on 2018-04-07 involved a ALEXANDER SCHLEICHER GMBH & CO. SEGELFLUGZEUGBAU ASW 20 CL, registration HB-1784, at Steinhausen, ZG, CH.

What was the probable cause of the accident?

The near-collision was caused by the failure of the pilot of the Piper PA-34-200 to recognize the presence of the glider tow formation, combined with the lack of effective visual signaling or recognized electronic collision warnings during the encounter.

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