This category includes light general aviation aircraft with a maximum take-off mass (MTOM) up to 2730 kg, up to 4 seats and a maximum cruising true airspeed up to 140 knots (KTAS).
Airspeed is directly affecting the ability to see ‑and ‑avoid. A combination of low antenna range and high closing speeds can lead to a very short time window for the pilots to react.
Therefore, the technology recommendation is split into aircraft with cruising speeds up to 140 knots TAS and aircraft with even higher cruising speeds. When applying for special financing, the aircraft owner is required to indicate their aircraft’s typical cruise speed in knots true airspeed (KTAS).
The Mode S transponders without ADS-B are widely adopted and is the minimum equipment in a CTR, TMA or class E airspace at and above 7’000ft MSL, or class G when flying below VMC conditions (refer to VRV‑L Art. 29). Of course, an existing Mode S transponder should be kept, and it is considered an e-conspicuity device. The recommendation below focuses on the interoperability with other aircraft categories and technologies.
Mode S transponders without ADS-B out should be supplemented by one of the recommended technologies, because it will not always be electronically visible (e.g. when there is no ground radar or TCAS interrogation).
Technology recommendation:
1. ADS-B out installation in combination with ADS-L in/out
Recommended due to the inherent benefits of a certified installation (e.g. known reliability, range, diversity). Ensures interoperability with traffic warning systems in other motor‑powered aircraft. This solution works well even at the highest aircraft speeds. The additional ADS-L receiver is needed to sense other traffic.
2. Traffic warning system in combination with ADS-B out or ADS‑L out
Recommended for traffic information, ideally with integration in certified avionics and the ability to receive traffic information via ADS-B, ADS-L, Mode S and FLARM. A traffic warning system might only receive traffic and not transmit. Therefore, a combination with ADS-B out or ADS-L out is recommended.
Please note that such a system might not always detect other traffic with Mode S transponders. Mode S transponders without ADS-B will only transmit data when replying to interrogations from a ground radar or a TCAS. The other aircraft’s transponder replies in the same mode as the interrogation. If a ground radar only interrogates in Mode A/C (e.g. Lukmanier Pass), the Mode S transponder will reply in Mode A/C and not show on certain traffic warning systems.
3. ADS-L in/out
Recommended as a cost-effective alternative to certified ADS-B out, however the non‑certified nature brings limitations pilots need to be aware of, such as varying degrees of system reliability, range or signal obstruction.
External antennas are recommended to improve signal strength in all directions (diversity). Without external antennas, the airframe might block the device’s signal almost completely in some directions. Installation of external antennas is possible with a standard change (CS‑STAN).
The signal obstruction issue could be reduced with multiple ground stations in range, which re‑broadcast emitted ADS-L signals. However, at the initial stages of FASST-CH, signal obstruction will remain an issue. Ultimately, diversity antennas are the best solution for air-to-air reception.
4. FLARM (or similar products) with ADS-L out
FLARM installations which support ADS-L out are recommended for new installations and as a software upgrade for existing installations.
Last modification 26.06.2025
