Airprox Serious incident Cessna 152 HB-TSN, Wednesday 18 September 2024

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Date:	Wednesday 18 September 2024
Time:	14:09 UTC
Type:	Cessna 152
Owner/operator:	Flugschule Eichenberger
Registration:	HB-TSN
MSN:	15284637
Year of manufacture:	1980
Fatalities:	Fatalities: 0 / Occupants:
Other fatalities:	0
Aircraft damage:	None
Category:	Serious incident
Location:	10 NM from Friedrichshafen - Switzerland
Phase:	En route
Nature:	Private
Departure airport:	St. Gallen-Altenrhein Airport (ACH/LSZR)
Destination airport:	Buttwil Airfield (LSZU)
Investigating agency:	STSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
A Cirrus SR22 (D-ECZZ) and a Cessna 152 (HB-TSN) were involved in a serious airprox in the Friedrichshafen Terminal Control Area (TMA).

The Cessna 152 departed St. Gallen-Altenrhein (LSZR) and exited its control zone (CTR). It subsequently flew, under good visual flight conditions, through the Friedrichshafen TMA slightly above its upper limit of 4500 ft AMSL, in Class E airspace.

The Cirrus SR22 had departed Olbia (LIEO) and was conducting an instrument approach to Friedrichshafen Airport. Descending from an altitude of 5000 ft AMSL, it followed the prescribed glide path toward runway 06. When it reached the upper limit of the TMA at 4500 ft AMSL, a near-collision occurred with HB-TSN.

The pilot of HB-TSN was initially in radio contact with St. Gallen Tower and, while over the Friedrichshafen TMA, established contact with the Zurich Information flight information service. The near-collision occurred during his initial call. He only gained visual contact with the approaching Cirrus shortly before the near-collision. He reported that the Cirrus had been displayed by his collision warning system.
The pilot of D-ECZZ was initially in radio contact with Alps Radar and, before the encounter with HB-TSN, switched to Friedrichshafen Tower. After receiving three traffic advisories from Friedrichshafen Tower, he gained visual contact with the approaching Cessna and reported “traffic in sight” 17 seconds before the near-collision (see Appendix 1). He also reported that the Cessna had been displayed by his collision warning system.
The air traffic controller at the Alps Radar approach unit was alerted to the hazardous convergence by the Short Term Conflict Alert (STCA) collision warning system 1 minute 44 seconds before the near-collision. He contacted Friedrichshafen Tower by telephone, requesting that a traffic advisory be issued to D-ECZZ. In addition, he attempted unsuccessfully to establish radio contact with HB-TSN.

The minimum separation between the two aircraft was 0.1 NM horizontal, 0 ft vertical.
The incident was rated ICAO Airprox Category A.

Causes
The near-collision between two motorised aircraft can be attributed to the following directly causal factor:
- The pilots did not visually perceive the other aircraft in time.
The investigation also identified the following systemic cause for the near-collision:
- One of the two aircraft was not in contact with the air traffic control centre, which could have warned it of the dangerous approach, due to its voluntary listening watch in the Transponder Mandatory Zone (TMZ) over Swiss territory.

Accident investigation: