We model the Sundstrand APS 2000 APU. It is FADEC controlled - and in our V1.0 it always starts up (below a certain altitude, iirc) and will not "break" if you don´t adhere to the various limits. I feel that this is realistic enough, because in 10 years of flying this plane I only had to refer to the starting limits only a few times (you can start it 3 times without any waiting, but then have to wait 30mins before the 4th and subsequent attempts). Usually the APU starts up just fine. the procedure is: Toggle APU switch to ON. Release. Ta-da! We plan to have a "wear and tear" model in future updates and versions - but I will vote strongly to not make it a "gamey" model. If you bust a limit, it usually does not mean that the affected component will fall apart into a 1000 pieces. The limits on operations are usually designed to keep the component running without damaging it in the long run. So if you have a limit of 2 minutes between start attempts, and you only wait 1:55, the starter most likely will not fail right away... I don´t think we will make this totally "realistic", because then you would have to fly the plane for thousands of hours before you see any "wear", but it will not be a "bust the limit by one degree and the plane will instantaneously combust" model, either. Some middle ground. Jan