Hi Take3Call5;
Actually I probably know the system that you have fairly well since all that you have had and now have were off shoots of what we have or decided to not do...
I completely understand the issues with doing something to the software and then effecting something else in the system. That is why we do a LOT of testing on all of our patches and then test them at all 20 facilities when we install them here. Guess what, even with doing that it doesn't always work. We had a failure just last month on a new patch due to those issues, but we do the install on the midnight shift and bring it back up before the traffic starts getting busy, so if the system flops rigth away, there isn't a lot of impact when we reload the old system and bring it back online...
As to the complexities of any sort of NAS system replacement, we completely understand that too and that is why we are now going with the thought of replacing small parts of the NAS one at a time and then turning them off one at a time. Do this until we get to the radar and data processing and then replace those. Don't try to do a big bang. There is too much at risk to do it that way, as well as a training nightmare for the work force. We don't let pilots get into a new aircraft with just a few days of training over a couple of month period. They go through a LOT of training and are taken off the line as it were to immerse in training. Obviously with our staffing in most of the busy parts of the world, we just can't do this. So do it the smart way. Go in baby steps and get the whole thing done over a course of years so that you have minor training issues that are easy to deal with and there is very little if any dissruption to the users.
regards