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Gulfstream V Training Captain's Questions and Answers

 FlightSafety KSAV

APU STARTING

What is the minimum oil temperature at which the READY light will illuminate?

There is no longer a minimum temperature requirement. However, once the MAIN AC BUSES are powered, the Right Main AC Bus will power the APU OIL HEATER which activates at 21°C and deactivates at 43°C automatically as long as the MAIN AC BUS is powered in all phases of flight.

At what temperature will the oil deprime solenoid activate? 

-6.6°C, It will also activate during every shutdown to prepare the APU for the next start.

What is the purpose of the OIL DEPRIME SOLENOID on the APU?

It prevents oil from going to the APU bearings during cold starts to prevent the starter from dragging down due to thick oil.

What are the limitations for starting the APU with external DC power? 

Wait 15 minutes between starts

If selected, when will the APU generator come on after APU start?

99% + 2 seconds

If selected, when will the APU Bleed Air come on automatically after APU start? 

60 seconds if the APU EGT is ‹ 150°C prior to start, 99% + 2 secs if APU EGT › 150°C, and immediately in flight, if the COP switches are configured as follows:

1. Both Bleed Air Switches are OFF
2. Both Pack Switches are OFF
3. Master Crank or Start Switch is ON
4. Engine (L or R) Start Switch ON

What is the difference between the amber APU ESSENTIAL and blue APU UNAVAILABLE messages and what do they mean?

• APU ESSENTIAL = APU is running while in flight, and a fault is detected which normally would cause the APU to shut down if not in the essential mode.
• APU UNAVAILABLE = APU is in non-essential mode and may not start or may shut down on the ground.

What will cause an automatic APU Shut down in flight or on the ground? 

APU FIRE

Describe a normal APU shutdown on the Ground and up to 20,000 feet?

Once the STOP switch is pressed, the APU RPM decreased at a rate of ½% per seconds for 60 seconds, when the rpm reaches 70% the APU SHUTS DOWN. The APU door will automatically start to close at 25% RPM and The APU MASTER switch may be turned off at 5% RPM.

Describe a normal APU shutdown above 20,000 feet?

Once the STOP switch is pressed, the APU will load shed and the APU RPM WILL remain at 100% for 1 minute, and then the APU will SHUTS DOWN. The APU door will automatically start to close at 25% RPM and The APU MASTER switch may be turned off at 5% RPM.

Why is there a requirement to turn off the Right Battery for an Inflight APU Start with one or both Main Generators powered?

Because both batteries produce too much torque and may ramp the APU starter past the APU Start envelope and automatically shut down.

When does the APU MASTER blue message come on?

5 minutes after APU shutdown or 5% RPM, which ever is first.

Is the APU Electronic Control Unit still powered after the APU MASTER Switch is deselected?

Yes, for 5 minutes.