Airborne Collision and Avoidance System — Page 491, Lesson 587

I want to walk you through the actions a flight crew must take when the Airborne Collision and Avoidance System — TCAS — gives you a Traffic Advisory, or TA, and a Resolution Advisory, or RA. This is the operational side of the system, the part that tells you exactly what to do with your hands and your eyes when the box starts talking. Let's start with the Traffic Advisory, the TA. A TA is an alert that tells you there's a potential threat out there, and it's a heads-up that a Resolution Advisory may follow. And a Resolution Advisory, remember, is the instruction that could actually require you to change your flight path. So when you get a TA, your job is to assimilate the information — take it in, understand where the traffic is — and then commence a visual search of that part of the sky. You're also preparing to respond to an RA if the situation worsens. Now here's the critical part: if you cannot see the potential threat, and it continues to give you cause for concern, you should seek advice from ATC. But note this hard rule — do not manoeuvre on the basis of a TA alone. A TA is information and preparation, not a command to move the aircraft. Now the Resolution Advisory, the RA. This is the command. When you receive an RA, you are to initiate the required manoeuvre immediately. And I want you to notice the full scope of that — you're adjusting flight path, aircraft power, and trim accordingly. It's not just turning the yoke; it's power and trim as well, because the manoeuvre has to be clean and controlled. While the pilot flying is executing that manoeuvre, the crew members not involved in executing it have a specific job: they confirm that the sky ahead is clear of other aircraft, and they continue the visual search for the established threat. And then, as soon as possible, you inform ATC of any deviation from an ATC clearance. That's a legal and operational obligation — you've deviated from your clearance, so ATC must know. Now let's talk about disregarding RAs, because there are very strict limits on when you may ignore one. The fundamental rule is this: manoeuvres should never be made in a direction opposite to that given in an RA. Why? Because the sense — the direction of the manoeuvre — may have been determined following an exchange of data with the established threat. TCAS has talked to the other aircraft's transponder, they've coordinated, and the sense is the result of that coordination. If you reverse it, you could fly straight into the very traffic you're trying to avoid. So when can you disregard an RA? Only under one specific condition: when pilots visually identify the potentially conflicting traffic and decide that no deviation from the current flight path is needed. That's it. Visual identification, and a decision that no deviation is necessary. There's a question in your book that tests this exact point, and I want you to notice the trap in it. One of the options adds an extra condition — that you must also have advised ATC of the other aircraft's proximity. That is not part of the rule. The rule is purely: visual identification of the conflicting traffic, and a decision that no deviation is needed. Advising ATC is not a precondition for disregarding an RA. And finally, there's the conflict between ATC and TCAS. If you receive simultaneously an instruction to manoeuvre from ATC and an RA, and both conflict, the advice given by TCAS should be followed. TCAS takes precedence over the ATC instruction in that moment of conflict. That's a firm operational priority. So to pull it together: TA means look, prepare, don't manoeuvre. RA means manoeuvre immediately, adjust path, power, and trim, clear the sky ahead, and tell ATC about any deviation. Never manoeuvre opposite to the RA sense. Disregard an RA only with visual identification and a decision that no deviation is needed. And when ATC and TCAS conflict, TCAS wins.