APU Flashcards by Darragh Doogan

Up to what altitude is electric power available?

41,000 feet.

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Up to what altitude are both bleed and electric power available?

23,000 feet.

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What is the maximum altitude for a battery start and for an AC network start?

-Battery start: 25,000 feet
-AC network start: 41,000 feet

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How many stages does the APU turbine have?

3 stages.

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What prevents coking in the fuel nozzles during APU shutdown?

The compressor forces air out the fuel nozzles.

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What operates the inlet guide vanes of the APU?

Fuel muscle.

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How many shafts does the APU have?

One (Single shaft)

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What type of compressor does the APU power section have?

A 2-stage centrifugal compressor

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How many fuel nozzles does the APU have?

12 fuel nozzles

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How many fuel manifolds are in the APU, and what are they called?

Two: Primary and Secondary

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Which APU fuel manifold is used during start?

The Primary manifold

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When do both APU fuel manifolds supply fuel?

At high speed (High N speed)

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What causes the secondary fuel manifold to begin supplying fuel?

Fuel pressure builds up and eventually overcomes the restrictors

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What components are driven off the APU accessory gearbox?

Starter, AC generator, lubrication unit, fuel control unit

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What does the ECB (Electronic Control Box) control?

Bleed valve, surge control valve, ignition unit, inlet guide vanes, inlet flap control

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Which valve does the ECB use to prevent compressor surge?

The surge control valve

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Which component controls the APU bleed valve?

The ECB (Electronic Control Box)

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What is the function of the surge valve in the APU, and where does it dump surges?

The fuel muscle operated surge valve is constantly modulating and will dump surges into the APU exhaust.

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How many EGT sensors (rakes) are installed in the APU exhaust?

There are 4 EGT sensors (rakes) installed in the exhaust.

What component in the APU monitors for overspeed, and where is it installed?

An overspeed sensor is installed in the gearbox.

How many hook latches and pin latches hold the APU doors together?

There are 3 hook latches holding the APU doors together, with a pin latch on either end of each door.

How many hours of APU operation does the oil level allow when the “OIL LEVEL: CHECK” message appears?

The oil level allows for 60 hours of APU operation when this message appears.

Where is the manual operation for the APU inlet flap available?

The manual operation for the inlet flap is available via the aft THS compartment.

How many switches control the position of the air intake flap actuator?

There are 2 limit switches and 2 position switches controlling the air intake flap actuator.

How can you bleed the APU fuel system?

Bleeding the APU fuel system is done from the APU compartment by pressing the push button, then opening the valve and bleeding the system.

What component assists in cooling the APU compartment and oil cooler?

A fan assists in drawing air into the APU compartment for cooling and also provides cooling air for the oil cooler.

How many mounts and tie rods secure the APU, and what is installed on the tie rods?

The APU is secured by 3 mounts and 7 tie rods, which have vibration isolators installed.

Where are the APU drains located, and what do they drain?

There are 2 drains aft of the APU door, one for engine drain and one for accessory drain (fuel, oil, water, etc.).

What module stores APU data, starts, shutdowns, and hours?

The Data Memory Module (DMM) stores APU data, including starts, shutdowns, and operational hours.

What is the position of the Inlet Guide Vanes (IGV) during APU start and engine start?

The IGV is closed during APU start to unload the shaft and fully open during engine start.

What are the three non-inhibited shutdown conditions for the APU?

1- Overspeed 2- ECB internal failure 3- Emergency

Where are the low oil quantity switch and electrical chip detector located?

At the bottom of the oil tank, which is also the bottom of the gearbox.

What additional components (temp related) are installed in the APU oil tank?

A low oil temperature sensor and an oil heater.

At what speed does the green EWD memo “APU Avail” appear, and when does the green "Avail" light on the start button illuminate?

At 95% N.

From where is the APU bleed air taken?

From the single-stage load compressor.

What is the standard oil pressure at 100% N?

About 65 degrees.

What indicates that the starter motor needs to be replaced?

If the green brush wear indicator is no longer visible.

At what speed does ignition turn on and off?

On at 7% N, off at 50% N.

At what speed does the de-oiling valve close if it was open?

60% N.

At what speed does the fuel metering valve open?

7% N.

How many supply and scavenge pumps does the APU lube unit have?

3 supply pumps and 4 scavenge pumps.

What does the de-oiling solenoid valve do?

It allows air into the inlet side of the pressure pump during specific start conditions (cold temp) and APU shutdown.

What happens if the oil temperature is low on start?

Oil bypasses the oil cooler via a thermal valve.

Where does the air-oil separator vent air?

Into the exhaust.

What will cause an auto shutdown on the ground but requires crew action in-flight?

A Low oil pressure indication or high oil temp indication.

When does the oil heater automatically turn on?

When the aircraft is powered up, the APU master switch is off, and oil temperature is less than 21°C.