Onceapilot - you must have been involved with some really bad APUs if you consider the Tristar unit to be a good one - it's one good point was that it was easy to change. The GTCP 660 in the 747 was far better. All the components could be replaced without dropping the unit and were easily accessible. It also has 2 generators - (most operators.) The Tristar speed and pneumatic control systems were unreliable I could go on and on!