What this relates to
Near-misses or collisions of aircraft in the air: The Airborne Collision Avoidance System (ACAS) exists to reduce this risk. These devices supply pilots with evasion instructions. The pilots are obliged to observe all messages immediately, even if the messages contradict the clearances or instructions from air traffic control.
Example
On approach to the airport, the commercial aircraft receives a conflict message with the order to climb immediately. The collision warning device has located a motorised aircraft performing aerobatics in the airspace beneath it.
Commentary on the 2023 figures
The evasion instructions (TCAS RA) reported in Switzerland since 2022 have been at a higher level than in previous years. This increase could be due to several factors, some of which are positive developments, for example:
- More transponders are in use. The increased number of transponders in operation on aircraft makes it possible to detect and identify other nearby aircraft more precisely. Consequently, the system can react more sensitively to potential conflicts and issue evasion instructions more frequently.
- Transponder Mandatory Zone (TMZ) being introduced in north-eastern Switzerland. The introduction of the TMZ has led to more aircraft operating in the defined airspace with switched-on transponders. This has increased the visibility of aircraft and the likelihood of evasion instructions being issued.
