TCAS/ACAS levels and advisories
TCAS interrogates other aircraft's transponders for position. Runs independently of ATC.
- ACAS = ICAO name for TCAS. Terms generally interchangeable.
- Fully compliant ACAS II = TCAS II software version 7.1 (COM 9.1).
- Intruder with no transponder, or Mode A only: invisible to TCAS. No traffic advisory (TA) or resolution advisory (RA).
Levels:
| Level | Advisories | Requires | Notes |
|---|---|---|---|
| TCAS I | TA only | Helps spot traffic visually. | |
| TCAS II | TAs + vertical-plane RAs | Mode S transponder |
Advisories:
- TA: proximate traffic and its relative position.
- Aid to visual acquisition. Prompt to prepare for possible RA.
- Do not manoeuvre on a TA alone. Search visually, query ATC (COM 9.6, 9.9(a)).
- RA: two types.
- Preventative: maintain or avoid a given vertical speed.
- Corrective: deviate from current flight path, e.g. "CLIMB".
Trap: treating a TA as a command; a TA only prompts visual search and ATC query.
References
- TC AIM COM 9.1, 9.6, 9.9