AUXILLARY POWER UNIT Flashcards
Is the solar APU a Variable or Constant rpm gas turbine? Where is it located?
It is a constant RPM engine, located in the tail.
What warning is there of rear bay over-temperature? What is the result?
Gen OHT and RBYOHT advisory lights on the APU panel. The APU will automatically shutdown.
With reference to the APU what does the ESU do?
Electronic Sequencer Unit, provides start sequencing, malfunction indications, fault monitoring
Where does starting power for the APU come from?
Right main bus, (28VDC) battery or external power.
Where is APU fuel obtained from?
Left fuel tank collector bay
What happens if the APU catches fire?
Fire warning light on APU panel, check fire DET warning and APU caution light. ESU shuts down APU, BTL light illuminates and fuel valve close light comes on. 15 seconds later the fire extinguisher fires (fire light and bottle light go out). If this does not occur can discharge manually.
What does APU bleed air supply?
De-ice (always on), aircon if bleed air on.
What light indications would you expect to see during APU start?
Start switchlight goes out as it reaches 70%, run light comes on, turn GEN on, check load (gen2), 20 seconds, Bleed air switch back on.
How do we arm the APU start circuits?
Press the APU PWR switchlight.
If the APU fuel pump fails prior to APU start are we able to start the APU?
The APU will inhibit starting.
How is APU electrical power fed into the aircraft bus system?
Right main feeder bus.
What happens if an APU generator fault is detected?
Gen will switch off with a WRN light.
Can APU and external DC power the aircraft system in parallel?
No, if DC power is supplied the Generators cannot be connected, however the battery master must be on to supply the overvoltage relay.
What faults will shut down the APU?
Overspeed, fire, overheat, high EGT, high oil temp, low oil pressure, underspeed..
What ways can we shut down the APU?
Bleed air off, Gen off, select PWR off.
What ventilation is provided for the APU?
Automatic blower in the ventilation duct which draws air out of the rear bay.
What sensors feed the APU?
RPM, EGT, oil temp, oil pressure
How many fuel pumps are provided for the APU?
FCU pump and an electric boost pump in the fuel supply line.
When is the APU fuel shutoff opened?
When APU power selected.
What happens of low fuel pressure is detected during start?
APU shuts down.
Where does APU bleed air flow to?
De-ice system then to the bleed air shutoff (APU bleed switch) then to the Pack
How many sensor loops are in the fire protection system?
one
Which parts of the APU are monitored and when (fire protection)?
Hot section and exhaust, whenever the right essential bus has power
How do we know the APU auto fire protection hasn’t worked?
APU BTL light remains illuminated
Are there any precautions to be taken when testing the APU fire circuit?
If the test button is held for more than 30 seconds it may cause activation of the extinguisher.
How does the APU blower work?
it sucks air out of the rear bay through the APU oil cooler and vents it overboard, when not in operation the inlet closes. the whole system is prevented from operating after a fire.
