G550 - APU
When starting the APU with external DC, a minute cooling period must be observed between start attempts.
The APU starter duty cycle is three attempted starts. If the APU does not start on the third attempt, there is a 1-hour wait before another attempt may be initiated. This allows the starter to cool down.
The APU uses a digital Electronic Control Unit. The APU ECU is located in the baggage compartment electronic equipment rack (EER).
The APU oil system reservoir is located on the left side of the APU and is an integral part of the accessory gearbox. The reservoir stores up to 5.18 quarts of oil for system use and must be replenished when the level reaches ____.
The reservoir can be serviced using the gravity fill port, or it can be pressure-filled from the remote oil replenishment system in the tail compartment.
The APU will automatically shut down in the essential mode if a low oil pressure situation develops.
The APU is guaranteed to start below:
There is a ____ cooling period between each start attempt when using external DC power.
The APU is in the essential mode any time it is airborne.
When running in flight, the APU electronic control unit (ECU) will open the surge valve to control surge potential at approximately:
The G500/550 APU provides an alternative source of electrical power on the ground and in flight up to ____.
The APU also automatically shuts down when the ECU observes an EGT exceedance. Three different EGT shutdown schedules are used by the ECU.
Two only. One schedule is used during acceleration up to 95%, and a second schedule is used when the APU is above 95% rpm.
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Selecting the APU STOP switch to OFF commands the ECU to initiate an APU cool-down period. The APU sheds loads at this time and enters one of two cool-down modes, depending on whether the aircraft is ____.
After the cool-down period, the ECU performs an APU shutdown. Once the shutdown is commanded and rpm has reached 5%, the ECU latches power for another five minutes. This provides power for post-run functions, such as EGT and speed indications.
Bleed-air augmentation valve (BAAV) will open to allow hot air from the bleed air manifold into the APU for starting above:
To increase high-altitude start capabilities, the oil system contains a sump heater which heats APU oil. It is located in the lowest point of the gearbox sump and uses aircraft power for the heating element. The heater is thermostatically controlled to come on at ____and turn off at ____.
The oil sump heater gets its power from the aircraft, independently from the APU electrical system.