Originally Posted by TheInquisitor
Action precipitated by an RA is mandatory and trumps any other ATC instruction - it has to be, otherwise you're kind of defeating the object of TCAS.
It is mandatory and it is a sound policy to always follow RAs IF and only IF all aircraft have TCAS, otherwise, the aircraft w/o TCAS is an unpredictable entity and TCAS RAs are based on predictability (ie - the other aircraft either reacts to its own RA, or if not TCAS equipped, continues in its present manner). Add in the latency of updates (~1 sec ish?) and you have a challenging situation.
I always here about TCAS would've saved the day on the Russian/DHL midair back in '02 and the controller bungled the job. He was working two sectors simultaneously and gave the Russians instructions counter to their TCAS. However, remove TCAS and the controller had a plan to deconflict the traffic - no issue. The issue was TCAS was involved directing the DHL to do something and, in this case, if both aircraft equipped with TCAS followed their RAs, it would have saved the day. The Russians, by not following TCAS, became unpredictable - the same as if they didn't have it.
My only 3 RAs have all come from fast jets climbing rapidly through my altitude - in ALL cases, my TCAS gave me a climb RA which simply makes the matter worse. TCAS gives me a climb because the offending aircraft is below me. In all cases, I was VMC, twice above cloud where I could not initially identify the "intruder", but it was simple to deduce what it was. I ignored all 3 RAs because, as the Captain, I have the obligation and responsibility for the safe conduct of the flight - technology notwithstanding. Since VMC and able to VID the "conflict" TCAS identified, I simply did nothing. Nor did I report this to anyone, although I would have been well within bounds to report a near-miss/airprox/HATR.
I'm a huge fan of TA-only right now - at least until ALL aircraft are fitted. I love the SA the "fishfinder" gives me - for now, I shall also use lateral offset to avoid RAs, or to augment. Of course, when VMC, the Mk1 eyeball is primary, with a good radar backup (when avail). Until such time as all aircraft are TCAS (or ACAS) equipped, I simply do not know what the "intruder" is going to do or how he is going to react. In the overwhelming majority of the cases, the RA will work well, however, there is still that percentage...