Another poitn worthy of throwing in here is that I think some of the TCAS learning points have got a bit muddled.
There is a very valid point that the aircraft you can see may not be the one that you are getting the RA about. There was a wonderful (from a training reinforcement point of view - I'm sure the blokes shat themselves) incident back in the early days. (Bear in mind the SOPs of the day permited an RA to be disregarded based on a visual spot.)
In a nutshell: The crew had two RAs in quick succession against two different aircraft. They saw the first target as they got the RA against the second one (still unseen). They assessed the second RA as being unnecessary but elected to fly it anyway, and then had aircraft 2 flash directly overhead (i.e.no horizontal miss, TCAS generated vertical miss).
The point is, don't let a visual spot throw you off making the RA vertical manoeuvre.
Misuses of the traffic display, with folks generating their own turns based on it - sometimes way in advance of an RA, and sometimes even turning safe separation into an RA - have a colourful past.
I would argue that if you can
see something at constant relative bearing and its getting bigger, then it doesn't matter if its the traffic causing the RA or not; its a collision risk.
Lets also throw in Anotherthings observation:
ATCOs are instructed not to pass turn instructions on receipt of an RA call from a pilot
Yes (though it wasn't always that way). But even so, you'd probably be giving avoiding action up until getting a 'tcas descent (or whatever)' call.
Lets throw in an example. Vectoring in towards a regional airfield, a grobbly day with a fair bit of low level cloud. Lets say 20 miles out, in level flight. Controller suddenly says something like "Callsign! Avoiding action! Turn right heading 090 - pop up traffic from low level". As you thumb the a/p disconnect and start your turn, your TCAS gets about halfway through saying 'Traffic' and then says "Maintain vertical speed - maintain" with a red sector above your current vertical speed (i.e. saying don't climb). What do you do? Surely we'd all maintain the current altitude and fly the turn. Wouldn't we?
pb