What about this:
747 off of JFK full of fuel taking off into the NAT tracks, operating at maximum available cruising altitude for the moment at FL360, ATC asks if they're able FL 370 for traffic earlier, they are not able that level.
Now my question IF TCAS asked them to climb for an RA, is the airplane going to get up there? Also does TCAS take that into account or is it completely separate from those systems?
Since airplanes flying long haul are often operating near or at their maximum cruising altitude for their current weight, what if the RA tells them to climb and they cannot? Then what?