Forum search FTW.
Go back and read the previous thread quoted by Glueball. In detail. There is too much dogma on this thread.
RAs should not be ignored. But if you think that any RA that is given to you is gaurunteed to be achieveable, you're cruising for a bruising.
If you have TCAS II on board, you are legally obligated to follow RA commands! To not do so, puts everyone at a risk far greater than not doing so.
Actually, that's not true.
There is an important distinction to be made between 'not following' (which is riskier, but only slightly) and 'manouvering opposite' (which is far far riskier).
This may seem like I'm laboring a point, but if you look at the really nasty TCAS incidents (including the ones that would have been collisions if there hadn't luckily been some horizontal separation) a regular feature is people manouevering opposite. Whereas there are plenty of times where RAs have not been followed and with low risk.
When pilots are told "follow the RA, always, thats all there is too it" then they are receiving incomplete guidance. The bean conters love it - a single sentence in an ops manual is cheap; proper training isn't.
It is very possible to receive an RA that is unachievable and/or otherwise unsafe. In those circumstance crew need to know what to do to minimise the risk. In my experience as a trainer if you tell people they mist follow the RA, and then give them a situation where they can't, there is a good chance they will do something really stupid unless they have a good alround knowledge of the system and other collision avoidance techniques.
To answer the Original Poster:
You follow any RA that is generated, whilst being sure to protect the aircrafts flight envelope. If the RA is a climb, and is not achievable, do your best to achieve the best rate of climb, even if its only a few hundred feet a minute, and get as close to the green arc/segment as possible.
UNDER NO CIRCUMSTANCES think "We cant get over him, we must descend!"
If you see the other aircraft, the curvature of the Earth will probably make it appear to be well above the horizon. UNDER NO CIRCUMSTANCES discard your RA in favour of your visual perception of relative altitude and commence a descent.
In other words UNDER NO CIRCUMSTANCES manoeuvre opposite the RA.
pb