SA 24: Use of the transponder and contact with air traffic control
In the course of the safety investigation concerning the serious incident (airprox) between the business jet Falcon 2000EX, CS-DLB and the glider Arcus, HB-3442, on 15 October 2017, west of Amriswil (canton of Thurgau), the Swiss Transportation Safety Investigation Board (STSB) identified a safety deficit and issued safety advice No. 24 in its final report No. 2350.
Target group(s)
Aero Club of Switzerland (AeCS) and all airspace users
Safety advice
The Aero Club of Switzerland should raise awareness among its members of the fact that increased IFR traffic is to be expected in Class E airspace which borders on Control Zones (CTR) and Terminal Control Areas (TMA) of regional airports such as St. Gallen-Altenrhein. Keeping the transponder switched on continuously and making contact with the aerodrome controller of the respective aerodrome to communicate their own position and flying altitude are the only possible way, besides ‘see and avoid’, to make a VFR aircraft detectable for IFR traffic.
Safety deficit
Outside of the Control Zone (CTR) and the Terminal Control Area (TMA), approaches and departures executed under Instrument Flight Rules (IFR) at St. Gallen-Altenrhein Airport take place in Class E airspace over considerable distances. For aircraft flying under Visual Flight Rules (VFR), transponder use is not compulsory in this airspace, nor is there any obligation to maintain radio contact with air traffic control. As a result, VFR traffic may remain completely unrecognised by the air traffic controller and only be detected by the IFR flight crew by means of visual identification (‘see and avoid’).