When the unit stops, the confusion shouldn't start

Don't prematurely pull the APU
Not all -100 units need to be pulled at 1,500 hours for hot section (HSI). Learn as much about your model engine as possible, and find out when it needs to be pulled for HSI. If you've got one of the higher mod standard turbine nozzles and one of the three higher mod standard turbine wheels, you don't schedule the APU at 1,500 hours anymore; you can schedule it at 2,100 hours.

To determine this, you have to look at turbine nozzle and turbine wheel part numbers, which should be recorded in the log book. Compare them to the manufacturer's service bulletins and maintenance manuals.

On all corporate -150 models, regardless of the Service bulletins, they went from 3,000 to 4,500 hours.

What should you expect for service life
Based on our experiences working with these engines, the amount of life service you can expect to get out of each engine varies among engine models and the type of operating you do. Corporates typically operate 100 to 300 hours a year, while Regionals can operate 225 hours a month. You should expect to get approximately the following life out of the following models of APUs (the Turbine Nozzle is the determining factor since it's exposed to the highest temperatures):
- 100E: 1200-1500 hours; used on the Challenger.
- 100G: 1400-1800 hours; used on the Gulfstream.
- 100A: 10 years (FOD can be a problem due to where the inlet is located — the inlet for the APU is behind right wheel well); used on the Falcon 50.
- 150F: 22 years (FOD can be a problem due to where the inlet is located — the inlet for the APU is behind right wheel well); used on the Falcon 900.

Get the service bulletins complied with
As a final thought on this engine: AlliedSignal has hundreds of bulletins out there. What we did is look at the different bulletins that will really extend the life of the engine and are worth it. We came up with the following three that we recommend as being critical:

• 6081, Improved Bearings.
There are six bearings that really should be replaced. For all six bearings it is less than a thousand dollars.

• 6114, Improved Clutch Shaft.
This is critical because if the shaft fails, it will destroy your gearbox.

• 6121, Improved Idler Gear.
There is a bearing that's failing, and this also can take out your gearbox.