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Cat A M15 Gas Turbine Engines > 15.18 Auxiliary Power Units (Level 1, 4 Questions) > Flashcards

15.18 Auxiliary Power Units (Level 1, 4 Questions) Flashcards

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1
Q

What type of engine is the APU?
A. Reciprocating piston engine
B. Small gas turbine (free turbine) turboshaft engine
C. Ramjet engine

A

B. Small gas turbine (free turbine) turboshaft engine

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2
Q

What does the APU supply?
A. Hydraulic pressure only
B. Electrical power and bleed air
C. Cabin pressurization only

A

B. Electrical power and bleed air

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3
Q

What is the main purpose of the APU on the ground?
A. Increase engine thrust
B. Operate the aircraft without ground support equipment
C. Reduce landing speed

A

B. Operate the aircraft without ground support equipment

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4
Q

When used on the ground, the APU is the primary source of what?
A. Air for wing de-icing
B. Bleed air for engine starting
C. Fuel for auxiliary systems

A

B. Bleed air for engine starting

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5
Q

When can the APU be used in flight?
A. Only during turbulence
B. As a backup for bleed air and AC power
C. To replace cabin crew oxygen

A

B. As a backup for bleed air and AC power

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6
Q

What is an advantage of the APU’s free turbine design?
A. Lower fuel pressure
B. Compressor is unaffected by free turbine load changes
C. Higher cabin pressure

A

B. Compressor is unaffected by free turbine load changes

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7
Q

What is the normal operating speed of a free turbine in the APU?
A. Varies with altitude
B. Constant
C. Decreases during engine start

A

B. Constant

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8
Q

Why is constant turbine speed important for the AC generator?
A. It reduces temperature
B. It ensures constant frequency
C. It limits oil usage

A

B. It ensures constant frequency

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9
Q

Where is the APU typically located?
A. Cockpit
B. Nose gear bay
C. Rear fuselage in an unpressurised fireproof compartment

A

C. Rear fuselage in an unpressurised fireproof compartment

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10
Q

What is the typical max altitude for APU start in-flight?
A. 10,000 ft
B. 15,000–17,000 ft
C. 30,000 ft

A

B. 15,000–17,000 ft

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11
Q

When is the APU often started during flight?
A. Cruise
B. During landing phase
C. During takeoff

A

B. During landing phase

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12
Q

Why is the APU started during landing phase?
A. To shut off main engines
B. To unload main engines’ pneumatic burden
C. To reduce fuel usage

A

B. To unload main engines’ pneumatic burden

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13
Q

How many main sections does the APU have?
A. Two
B. Three
C. Four

A

B. Three

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14
Q

What are the three main sections of the APU?
A. Power, fuel, and electrical
B. Electrical, cooling, and generator
C. Power, bleed, and accessory gearbox

A

C. Power, bleed, and accessory gearbox

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15
Q

What is the function of the bleed section?
A. Fuel cooling
B. Drives the generator
C. Provides bleed air to the pneumatic system

A

C. Provides bleed air to the pneumatic system

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16
Q

What may some APUs use to provide pneumatic compressed air?
A. Main engine
B. Load compressor
C. Turbocharger

A

B. Load compressor

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17
Q

What are the components of the APU power section?
A. Compressor, combustion chamber, and turbine
B. Load compressor, EGT, and fan
C. Starter motor, oil cooler, and turbine

A

A. Compressor, combustion chamber, and turbine

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18
Q

What type of combustion chamber is used in modern APUs?
A. Can-type
B. Annular
C. Reverse-flow

A

B. Annular

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19
Q

What happens during an APU fire?
A. EGT increases
B. Manual cooling starts
C. Fire extinguishers activate automatically

A

C. Fire extinguishers activate automatically

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20
Q

What does the power section drive?
A. Only the load compressor
B. Compressor and gearbox
C. Wing anti-ice

A

B. Compressor and gearbox

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21
Q

What does the accessory gearbox drive?
A. Only the generator
B. All APU accessories
C. Landing gear

A

B. All APU accessories

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22
Q

At what speed does the APU supply the AC generator?
A. Variable
B. Depends on engine bleed
C. Constant

A

C. Constant

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23
Q

How many control modes does the APU control unit have?
A. Two
B. Four
C. Three

A

C. Three

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24
Q

What is controlled during the start mode?
A. Generator output
B. From start to 100% speed
C. Load compressor inlet

A

B. From start to 100% speed

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25
What does normal speed mode maintain? A. Rotor thrust B. APU at 100% speed C. Generator temperature
B. APU at 100% speed
26
What does shutdown mode do? A. Increases cooling fan speed B. Shuts engine generators C. Monitors and controls shutdown
C. Monitors and controls shutdown
27
What begins the APU start sequence? A. Fuel pump on B. Selecting master switch C. Starting the engines
B. Selecting master switch
28
What happens first in the APU start sequence? A. Cooling fan runs B. Combustion begins C. System test and inlet door opens
C. System test and inlet door opens
29
What happens if start takes too long? A. Start continues anyway B. APU control stops the sequence C. Generator starts
B. APU control stops the sequence
30
Why is long low-speed operation avoided? A. Causes oil loss B. Increases thrust C. Causes high thermal stress
C. Causes high thermal stress
31
What signals are used to maintain constant speed? A. Bleed and fuel pressure B. EGT and RPM C. APU speed and torque motor
C. APU speed and torque motor
32
What happens when bleed air demand increases? A. Exhaust gas temperature rises B. APU slows down permanently C. Less fuel is added
A. Exhaust gas temperature rises (More fuel is added)
33
When can APU be shut down? A. Immediately after use B. Only during flight C. After operating without load
C. After operating without load
34
How long is the APU cool-down period? A. 5–10 mins B. 0–120 seconds C. 3 minutes fixed
B. 0–120 seconds
35
What stops fuel flow during shutdown? A. Bleed valve closes B. APU controller closes combustion fuel supply C. Cooling fan turns on
B. APU controller closes combustion fuel supply
36
Where is APU fuel taken from? A. Nose tanks B. Centre tanks C. External tank
B. Centre tanks
37
Where do APU fuel lines run? A. Over the wing B. Nose to cockpit C. Along the aft cargo compartment wall
C. Along the aft cargo compartment wall
38
What ensures fuel pressure? A. Fuel evaporator B. At least one pressure switch C. Cabin bleed switch
B. At least one pressure switch
39
Why is positive pressure important in fuel line? A. Prevent fire B. Prevent surging C. Prevent cavitation
C. Prevent cavitation
40
What are the two sub-systems in the APU air system? A. Power and exhaust B. Bleed and cooling air C. Fuel and oil
B. Bleed and cooling air
41
What does the cooling system do? A. Power the AC generator B. Supply oil cooler and APU compartment ventilation C. Cool bleed ducts
B. Supply oil cooler and APU compartment ventilation
42
What are the tasks of the bleed system? A. Fuel mixing B. Bleed supply, surge protection, load compressor control C. Emergency generator cooling
B. Bleed supply, surge protection, load compressor control
43
What must happen to open the APU bleed valve? A. Cabin lights on B. APU switch ON and start complete C. Load compressor shut down
B. APU switch ON and start complete
44
What closes the APU bleed valve on shutdown? A. EGT increase B. Pilot override C. Shutdown signal de-energizes solenoid
C. Shutdown signal de-energizes solenoid
45
What component cannot be turned off in the load compressor system? A. Surge valve B. Load compressor C. Cooling fan
B. Load compressor
46
What controls air into the load compressor? A. Exhaust dampers B. IGVs (Inlet Guide Vanes) C. Boost fan
B. IGVs (Inlet Guide Vanes)
47
What happens to IGVs when APU bleed is ON? A. Fully open at once B. Move to partially open C. Close to reduce noise
B. Move to partially open
48
When are IGVs fully opened? A. To start air conditioning B. At high altitude C. During engine start and max cabin cooling
C. During engine start and max cabin cooling
49
How can surging be prevented in APUs without a load compressor? A. Close all valves B. Use anti-surge valve C. Change bleed valve timing
B. Use anti-surge valve
50
What happens if airflow behind load compressor drops? A. Bleed valve closes B. Surge control valve opens C. Generator disconnects
B. Surge control valve opens
51
What system is better for surge protection? A. Manual reset B. Anti-surge C. Surge protection system
C. Surge protection system
52
What triggers automatic APU shutdown? A. Generator load B. Engine fire C. APU control unit
C. APU control unit
53
What happens in automatic shutdown? A. Fuel slowly reduces B. Shutdown after delay C. No cool-down period
C. No cool-down period
54
Where are emergency shutdown switches located? A. Crew bunks B. Nose gear, wheel well, and refueling station C. Flight deck ceiling
B. Nose gear, wheel well, and refueling station
55
What activates APU fire extinguishing on the ground? A. Cabin crew B. Ground hydraulic pressure C. Automatic system
C. Automatic system
56
What system activates shutdown during fire? A. Surge protection system B. Fire switch C. APU fuel pump
B. Fire switch
57
What are signs of APU shutdown activation? A. Torque drop B. Shutdown without cool-down C. Inlet door stuck
B. Shutdown without cool-down
58
What provides EGT and speed data to APU controller? A. IGVs B. ECB (Electronic Control Box) C. Cabin sensors
B. ECB (Electronic Control Box)
59
When does the APU control unit perform system tests? A. After shutdown B. Before acceleration C. During start sequence
C. During start sequence
60
What causes higher EGT during APU operation? A. Less bleed air B. Higher fuel pump pressure C. More bleed air demand
C. More bleed air demand
61
What do the inlet guide vanes (IGVs) do in the APU load compressor system? A) Regulate oil pressure B) Control airflow into the load compressor C) Open and close the exhaust duct
B) Control airflow into the load compressor
62
When the APU bleed switch is set to ON, how do the inlet guide vanes react initially? A) Fully open B) Fully close C) Move to a partially open position
C) Move to a partially open position
63
What causes the inlet guide vanes to move to the fully open position? A) Cabin temperature decrease B) Main engine start and cabin cooling needs C) Emergency fire shut-down
B) Main engine start and cabin cooling needs
64
What does the surge control valve do if airflow behind the load compressor decreases or stops? A) Closes fuel supply B) Opens to release pressure C) Activates the cooling fan
B) Opens to release pressure
65
What is the better method of preventing APU compressor surge? A) Anti-surge valve B) Manual bleed valve C) Surge protection system
C) Surge protection system
66
Where does the anti-surge valve discharge air? A) Cargo compartment B) Exhaust duct C) Fuel tank
B) Exhaust duct
67
Why is the APU often started during the landing phase? A) To provide backup cabin heating B) To unload the engines’ pneumatic burden and save compressor air for go-arounds C) To power the landing gear motors
B) To unload the engines’ pneumatic burden and save compressor air for go-arounds

Cat A M15 Gas Turbine Engines (18 decks)

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