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Traffic collision avoidance

PostPosted: Thu Mar 01, 2018 2:58 pm
by CaptainMD
Hello PE,

The 737 800 I fly has a traffic collision avoidance system (TCAS).

When my TCAS gives me a warning of possible traffic conflict, what should I do? I ask because there may be a time where ATC can’t get to me.

Should I contact ATC and let them know immediately and wait for instructions or

Should I take it upon myself to evade in the safest way possible, return to my ATC instructions, and then notify ATC on what happened?

How about for general aviation aircraft with no TCAS? What do you do if an another aircraft is too close for comfort and your instincts are telling you that ATC is not going step in time?

Thanks PE!

Re: Traffic collision avoidance

PostPosted: Thu Mar 01, 2018 3:48 pm
by Kevin_atc
You need to know the difference between a TA (traffic advisory) and an RA (resolution advisory). A TA is when your TCAS projects potential traffic something like 40 seconds out. This is simply an advisory for you to know that traffic is there and there is no need for you to say anything to ATC unless you truly feel unsafe. An RA requires mandatory action by the pilot to either climb or descend (whichever one the TCAS tells you to do) in order to miss imminent traffic that the TCAS believes you are in serious danger of hitting. In the RW, if both aircraft involved are equipped with TCAS, the systems talk to each other and one will instruct the pilot to climb while the other will instruct the pilot to descend.

If you receive an RA, you must do what it says and once you have reacted to it, you need to advise ATC that you are “responding to an RA” to which the controller should do nothing as they are no longer responsible for separation of you and the other aircraft since TCAS should be fixing the situation. This is also to avoid ATC issuing conflicting instructions. You should also advise ATC when you are clear of the conflict and I believe you are supposed to return to your previously assigned altitude once it is all over.

Keep in mind- just because you get an RA does NOT mean that ATC failed to separate you with another aircraft. Common instances of RAs are due to aircraft climbing or descending at fairly quick rates that are assigned altitudes just 1000ft above or below you. TCAS believes their vertical speed is such that it is creating an imminent situation since it does not know what altitude the other aircraft is assigned. This is common with military aircraft or even Southwest from time to time when they are really putting the 737’s performance to the test! :P

As far as “general aviation” aircraft, I assume you mean VFR aircraft. You will get the same TA or RA with VFR aircraft as you would with IFR so just react accordingly as mentioned above.

Re: Traffic collision avoidance

PostPosted: Thu Mar 01, 2018 5:22 pm
by CaptainMD
This makes perfect sense and clears up my confusion.

Thank you for your time Kevin!