TCAS/ACAS RA response and phraseology
Responding to an RA (COM 9.6 unless noted):
- Treat every TA/RA as genuine unless intruder positively identified and assessed as neither threat nor hazard.
- Initial vertical-speed response within 5 seconds of RA.
- RA prevails over any ATC instruction or clearance.
- PIC may deviate from ATC clearance or instruction to the extent necessary for collision avoidance manoeuvre on ACAS RA (or TAWS/GPWS alert) (CAR 602.31(3)).
- Alter flight path minimum extent necessary. No aggressive manoeuvring needed: RAs predicated on 1/4 G (COM 9.9(b)).
- Stop RA climb or descent once RA ends (COM 9.7).
- Responding to an RA is a reportable aviation incident.
- Stall warning, wind shear alert, or TAWS/GPWS warning takes precedence over RA, especially below 2,500 ft AGL.
ATC contact:
- Notify ATC as soon as possible at deviation start and at deviation end (COM 9.9(c)).
- Right after manoeuvre, comply with last clearance received and accepted, or instruction received and acknowledged (CAR 602.31(4)).
- With flight service specialist: limit TCAS talk to stating RA response. Use discretion asking about TCAS-display traffic (RAC 1.1.2.2).
Phraseology (COM 9.10, Table 9.3):
| When | Transmit |
|---|---|
| Starting to deviate to comply with an RA | "TCAS RA" |
| RA response done, returning to clearance | "CLEAR OF CONFLICT. RETURNING TO (assigned clearance)." |
| RA response done, clearance resumed | "CLEAR OF CONFLICT. (assigned clearance) RESUMED." |
| ATC clearance contradicts the active RA | Follow the RA, transmit "UNABLE, TCAS RA" |
Controller replies "ROGER" (or an alternative instruction) at each stage.
Trap: RA beats ATC, but stall warning, wind shear alert, or TAWS beats RA, especially below 2,500 ft AGL.
References
- TC AIM COM 9.6, 9.7, 9.9, 9.10 Table 9.3
- TC AIM RAC 1.1.2.2
- CARs 602.31(3)
- CARs 602.31(4)