Podcast
Questions and Answers
What component does the GARRET 36-280 use for monitoring and control?
What component does the GARRET 36-280 use for monitoring and control?
What happens when the low oil pressure light illuminates?
What happens when the low oil pressure light illuminates?
Which APU model has a 60-second cooldown option?
Which APU model has a 60-second cooldown option?
What does the APU fire warning light indicate?
What does the APU fire warning light indicate?
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Which model uses a maintenance light to indicate non-critical failures?
Which model uses a maintenance light to indicate non-critical failures?
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What happens when the APU turbine speed exceeds its allowable rpm?
What happens when the APU turbine speed exceeds its allowable rpm?
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What type of compressor does the GARRET 85-129 feature?
What type of compressor does the GARRET 85-129 feature?
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What does the APU fire control handle do when pulled?
What does the APU fire control handle do when pulled?
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What type of impellers does the SUNDSTRAND APS 2000 use?
What type of impellers does the SUNDSTRAND APS 2000 use?
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Which of the following indicates a critical failure in the APU?
Which of the following indicates a critical failure in the APU?
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What is the purpose of the APU in an airplane?
What is the purpose of the APU in an airplane?
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How much KVA can the APU generator supply during flight operation?
How much KVA can the APU generator supply during flight operation?
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What feature automatically transfers power to an alternate generator when needed?
What feature automatically transfers power to an alternate generator when needed?
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Which component converts 115V AC to 28V DC power?
Which component converts 115V AC to 28V DC power?
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What is the first action taken when ground power is available?
What is the first action taken when ground power is available?
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What is the maximum load displayed by the generator AC ammeter?
What is the maximum load displayed by the generator AC ammeter?
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Which of the following statements is true about operating the APU bleed air?
Which of the following statements is true about operating the APU bleed air?
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What happens to the APU in the event of overspeed?
What happens to the APU in the event of overspeed?
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What is a feature of the APU designed to minimize exhaust noise heard by passengers?
What is a feature of the APU designed to minimize exhaust noise heard by passengers?
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What is the role of the Constant Speed Drive (CSD) in the electrical power system?
What is the role of the Constant Speed Drive (CSD) in the electrical power system?
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Study Notes
Electrical Power System
- Three electrical generators power the aircraft (two engine driven, one APU driven)
- APU provides self-sufficiency, supplying on-ground electrical power
- Automatic Bus Transfer System increases electrical power reliability
- Onboard power system annunciator and test modules monitor and detect malfunctions
Constant Speed Drive (CSD) and Generator
- CSD and generators are driven by each engine to produce 115 volts, 400Hz, three-phase AC power.
- Each CSD supplies 50 KVA.
- A Variable Speed Constant Frequency (VSCF) generator also produces 50 KVA
- Transformer/Rectifier units convert 115V AC to 28V DC for other systems.
- The APU generator provides 50/60 KVA (ground/flight).
APU Generator Bus Switches
- Connecting APU generator to generator buses #1 or #2.
- Disconnecting from #1 or #2 generator buses.
- APU can supply power to both generator buses during ground operations. During flight, APU can only power one generator bus.
Ground Power and Bus Transfer
- Enables use of ground power if available
- Tripping engine/APU generators from buses when using ground power.
- Automatic bus transfer system switches to the opposite generator if needed.
- Isolates DC systems when the transfer switch is shut off.
Auxiliary Power Unit (APU)
- Garrett 85-129 and 36-280 models are used.
- Sundstrand APS 2000 system controls and indicates APU operation.
- APU mounted on accessory drive pad.
- 60 KVA ground power, 50 KVA flight operation.
- Supplies bleed air for air conditioning (and engine startup), optimizing takeoff.
APU Starting
- APU starts with airplane battery or external DC power.
- Automatic shutdown happens with overspeed, high oil temperature, low oil pressure, or fire.
Exhaust Noise Reduction
- Noise reduced by acoustically treated inlet and exhaust ducts, and distance from cabin and ground service points.
APU Access and Maintenance
- APU readily accessible for inspection, maintenance, or removal through large fuselage access door.
Garrett 85-129 Components
- Two-stage centrifugal compressor with one radical inflow turbine.
- Accessories grouped at the front.
Garrett 36-280 Components
- Two centrifugal impellers and a single centrifugal turbine with a containment ring.
Fire Protection System
- APU housed in a fire protection shroud to contain fires.
- Fault causes "DET INOP" light and master warning lights activation.
Controls & Indicators
- Panel located on the forward head panel
- Includes APU switch (on/off/start positions, cooldown option)
- Maintenance light illuminates when oil tank is low.
- Provides indicators on the APU fire system
- Includes lights to warn of non-critical and critical failures.
- Oil low pressure
- Overspeed condition
- Critical part failure.
- Contains AC ammeter to display current.
- Provides exhaust gas temperature indicator
APU Fire Protection Controls
- Illuminated red light = APU fire.
- Fire warning horn when fire detected.
- APU fire control handle activates system
- Bottle discharge switch triggers fire suppression.
Pneumatics
- APU pressurizes air for engine starting
- Air source obtained from onboard APU or external ground cart.
- Uses 5th stage compressor air section for flight, and 9th stage for low-engine.
- Precooler system to control air temperature.
- APU used for air conditioning up to 17,000 ft altitude
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