Auxiliary Power Unit (APU) Operation Quiz
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Questions and Answers

Where is the APU located in an aircraft?

  • In the unpressurized tail cone (correct)
  • Above the passenger cabin
  • Near the main landing gear
  • In the cockpit area

What powers the APU starter?

  • Pneumatic power from engines
  • AC power
  • Hydraulic power
  • DC powered electric starting motor (correct)

Which function does the APU NOT perform?

  • Serving as the primary engine power source (correct)
  • Providing bleeds air for air conditioning packs
  • Supplying electrical power to the aircraft system
  • Operating engine starters

At what altitude is the APU limited to supply only one pack?

<p>From 15,000 to 20,000 feet (A)</p> Signup and view all the answers

What is provided by the APU during takeoff to avoid thrust reduction?

<p>Bleed air for environmental control packs (B)</p> Signup and view all the answers

What component provides automatic control of the APU?

<p>Electronic Control Box (ECB) (B)</p> Signup and view all the answers

What is the maximum aircraft altitude that the APU generator can provide electrical power?

<p>FL390 (D)</p> Signup and view all the answers

Which of these is a function of the APU during flight?

<p>Supplying bleed air for engine operation (D)</p> Signup and view all the answers

Which condition must be met for the APU starter to activate?

<p>The APU Master switch and Start pushbutton must both be ON. (D)</p> Signup and view all the answers

What is the maximum altitude for an in-flight battery start of the APU?

<p>25,000 feet (B)</p> Signup and view all the answers

Under what condition will the APU fuel flow be controlled by the ECB?

<p>During normal operation with engine generator power. (B)</p> Signup and view all the answers

What happens to the APU air intake flap when the APU is shut down?

<p>It closes automatically. (A)</p> Signup and view all the answers

Where are the main APU controls located?

<p>On the overhead panel of the flight deck. (C)</p> Signup and view all the answers

Which switch must be ON for the APU generator to operate?

<p>APU GEN switch (B)</p> Signup and view all the answers

How is the APU fire extinguisher deployed in the event of a fire?

<p>It is automatically discharged on the ground. (A)</p> Signup and view all the answers

What indicator appears on the ECAM APU page to confirm the flap is fully open?

<p>green FLAP OPEN (C)</p> Signup and view all the answers

What will occur if the APU start button is pressed before the flap is open?

<p>The start sequence will pause until the flap is open. (D)</p> Signup and view all the answers

What safety feature is provided for ground operation with the APU?

<p>The APU can operate without crew supervision. (D)</p> Signup and view all the answers

What does the APU BLEED pushbutton switch control when the APU is running?

<p>Supplies APU bleed air to the pneumatic system. (A)</p> Signup and view all the answers

What is displayed on the ECAM APU page during APU operation?

<p>APU bleed air configuration and APU generator operation. (B)</p> Signup and view all the answers

What will prompt an advisory on the ECAM APU system display page?

<p>Low oil quantity. (B)</p> Signup and view all the answers

What happens when the APU reaches approximately 95% N?

<p>The blue ON light in the APU START pushbutton extinguishes. (D)</p> Signup and view all the answers

What is the purpose of the check valve installed in the output of APU bleed air?

<p>To prevent backpressure from external sources. (D)</p> Signup and view all the answers

When should the APU bleed air typically be turned OFF before shutting down the APU?

<p>Immediately after engine start. (A)</p> Signup and view all the answers

What indication remains visible during the APU cool-down cycle?

<p>APU AVAIL memo. (D)</p> Signup and view all the answers

If the APU bleed was not in use prior to turning the APU MASTER switch to OFF, what will happen?

<p>The APU will immediately shut down. (C)</p> Signup and view all the answers

What should be observed on the ECAM APU page as soon as the APU generator is online?

<p>All generator displays will show normal parameters. (A)</p> Signup and view all the answers

What effect does pressing the APU BLEED switch to ON have on the ECAM APU page?

<p>It replaces the APU AVAIL with APU BLEED. (B)</p> Signup and view all the answers

What happens if you select the APU MASTER switch back to ON during the cool-down cycle?

<p>The cool-down cycle will be interrupted. (B)</p> Signup and view all the answers

How long does the APU typically continue to operate for proper cooling after bleed air use?

<p>60 to 120 seconds. (C)</p> Signup and view all the answers

Why is it important to monitor the ECAM page after turning off external power?

<p>To observe APU generator readiness. (D)</p> Signup and view all the answers

What occurs on the ECAM APU page when the APU bleed air switch is OFF?

<p>The APU BLEED memo changes back to APU AVAIL. (D)</p> Signup and view all the answers

Flashcards

Where is the APU located?

The Auxiliary Power Unit (APU) is located in the tail section of the aircraft, providing both electrical and pneumatic power. It enables the aircraft to operate independently of ground support equipment.

What does the APU provide?

The APU is a self-contained unit that supplies both electrical and pneumatic power to the aircraft, enabling it to operate without external support.

How does the APU generate power?

The APU uses a single-spool gas turbine engine to power an accessory gearbox, which drives a generator and connects to the APU starter. This system provides electrical power to the aircraft and supplies bleed air for various purposes.

What are the APU ground functions?

On the ground, the APU supplies electrical power to the aircraft's systems and bleed air to operate the air conditioning packs and engine starters.

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What is the role of the APU during takeoff?

During takeoff, the APU can supply bleed air to the air conditioning packs, preventing a reduction in engine thrust. This enhances takeoff performance.

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What are the APU's in-flight functions?

In flight, the APU can provide bleed air to the air conditioning packs and engine starters, with limitations at higher altitudes.

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What is the role of the APU during in-flight emergencies?

The APU can provide electrical power to one side of the aircraft's electrical system when an engine generator is inoperative, ensuring essential power in such circumstances.

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What is the maximum altitude for APU electrical power?

The APU generator can provide electrical power up to the maximum certificated aircraft altitude, ensuring reliable electrical power for most flight operations.

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APU Flap Requirement

The APU will not start unless the air intake flap is fully open.

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APU Battery Start Altitude Limit

The APU can be started using battery power, but only up to a maximum altitude of 25,000 feet.

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APU Oil System

The APU has a dedicated oil system. If the oil level is low, an alert will appear on the ECAM.

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APU Fuel System

The APU draws fuel from the aircraft's fuel system through a valve on the left side.

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APU Exhaust

The APU exhaust is directed directly out of the back of the aircraft.

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APU Fire Detection & Suppression System

The APU features an automatic safety system that detects and shuts down in case of fire. It also has a fire extinguisher that automatically discharges on the ground.

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APU Controls

The APU's controls are located on the overhead panel in the flight deck, including the Master Switch, Start Pushbutton, and Bleed Switch.

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APU Starting Sequence

The APU Master Switch must be activated and the Flap must be open before the APU will start.

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APU Generator

The APU's generator can provide power to the aircraft, but it only comes online when the external power and engine generators are off.

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APU Air Intake Flap

The APU's intake air flap is controlled by the Electrical Control Box (ECB). It opens to allow air into the APU compressor during operation.

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APU Indications

The APU's operation is indicated on the ECAM APU page.

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APU Bleed Switch

The APU BLEED switch on the Air Conditioning panel controls the supply of APU bleed air to the pneumatic system. It is typically off when the engines are running.

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APU Power Sources

Normal electrical power for APU start can be provided by engine driven generators, an external power source, or the aircraft's battery.

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APU Fire Switch

The APU FIRE switch can shut down the APU and release fire suppression agent in case of an APU fire.

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What is the APU?

The APU (Auxiliary Power Unit) is an independent power source that provides electrical power and bleed air to the aircraft when the main engines are off.

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How is the APU started?

The APU is started using a sequence of steps: first the starter engages, then the ignition is turned on, followed by the fuel.

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Why doesn't the APU generator automatically come online?

The APU generator will not automatically come online. It needs the higher priority external power source to be turned off first.

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What does the ECAM APU page show when the APU generator is operational?

When the APU generator is powering the aircraft, the ECAM (Electronic Central Automated Monitoring) APU page displays status information, including generator output and bleed air operation.

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What does the APU bleed air do?

The APU bleed air provides air to the aircraft systems, including climate control and pressurization.

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How does the APU bleed valve prevent back pressure?

The APU bleed air valve closes when the APU bleed air is turned off, preventing back pressure from other air sources.

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What is the APU cool-down cycle?

The APU is equipped with an automatic cool-down cycle that operates for 60 to 120 seconds after the APU bleed air is turned off to allow for proper cooling.

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Why should the APU bleed air be turned off after engine start?

The APU bleed air should be turned off as soon as possible after the main engines are started to prevent engine exhaust gases from being ingested into the air conditioning system.

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What does turning the APU MASTER switch to OFF do?

The APU MASTER switch to OFF initiates the APU shutdown process, which may be delayed for 60 to 120 seconds for the cool-down cycle.

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How can you interrupt the APU shutdown during the cool-down cycle?

The APU shutdown can be interrupted during the cool-down cycle by selecting the APU MASTER switch back to ON as long as the APU AVAIL memo is in view.

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What happens when the APU MASTER switch is turned OFF without using bleed air?

If the APU bleed air was not in use before turning the APU MASTER switch to OFF, the APU will shut down immediately.

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What is a battery start for the APU?

An APU start can also be performed without external power. This is called a battery start.

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How is the APU started with a battery start?

During a battery start, the APU MASTER switch is turned ON, and the aircraft's battery power is used to start the APU.

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What are the indications like during a battery start?

The indications during a battery start are simpler compared to a normal start, as the ECAM is not operational.

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Study Notes

Auxiliary Power Unit (APU) Operation

  • Location: The APU is situated in the unpressurized tail cone, providing self-contained electric and pneumatic power.
  • Self-Sufficiency: It is designed to operate independently without external ground support equipment.
  • Power Generation: A single-spool gas turbine engine, driving an accessory gearbox for electrical and pneumatic outputs.
  • Electrical Provision: Powers the aircraft electrical system, supporting operations like engine starting.
  • Pneumatic Supply (Bleed Air): Provides air for air conditioning packs and engine starters, both on the ground and in flight.

APU Operation During Ground Operations

  • Electrical Power Source: Can utilize an engine-driven generator or an external power source.
  • Start Sequence (Normal Power):
    • Select the APU MASTER switch.
    • Observe the ECAM APU page display.
    • Watch for the air inlet flap to open (FLAP OPEN).
    • Press the APU START pushbutton.
    • Monitor RPM, EGT, and the AVAIL light.
    • Turn OFF external power to empower the APU generator.
    • Select the APU BLEED switch if needed.

APU Operation During Flight Operations

  • Maximum Electrical Power: The APU generator can deliver power until approximately FL390.
  • Bleed Air Usage in Flight:
    • Maximum operation for 2 packs up to 15,000 feet, limited to 1 pack between 15,000 and 20,000ft. Actual altitudes dependent on ISA temps. Specific details in the flight manual.
  • Electrical Power during Flight: Can provide power to one side of the aircraft's electrical system if an engine generator is inoperative.
  • Start Sequence (Battery Power): Similar sequence as in ground start, but only the battery powers the APU. Only ECAM page is not available. Also, no exterior power options available.
    • APU MASTER switch on.
    • Observe the START light.
    • Watch APU for RPM at 95%.
    • Monitor for APU AVAIL light.

APU Shutdown

  • Automatic Cool-Down Cycle: APU will continue running for a period of 60-120 seconds if the bleed air was on before shutdown for complete cooling.
  • Bleed Air Consideration: APU bleed is normally turned off before shutting down the APU.
  • Manual Selection for Shutdown: Turn the APU MASTER switch OFF. If there is no bleed air, the APU shuts down immediately and the display indicates flap closed.

APU Controls

  • Flight Deck Panel: Includes APU MASTER, START, BLEED, GEN, and FIRE controls/indicators.
  • External Nose Gear: APU Shut-Off button and FIRE warning light.

APU Indicators and Displays

  • ECAM APU Page: Automatically displayed after start, showing EGT, Compressor RPM, bleed air configuration, generator operation status, and flap position.
  • Warnings and Abnormal Situations: Oil quantity low. Alerts are displayed on the ECAM APU page.
  • E/WD Display: Provides additional information (AVAIL, BLEED).

APU Safety on the Ground

  • Automatic Operation: Ground Operation is mostly unsupervised once started.
  • Fire Protection: Equipped with fire detection, warnings, and automatic shutdown, and automatic fire extinguisher discharge (on the ground).

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Description

Test your knowledge on the operation of the Auxiliary Power Unit (APU) in aircraft. This quiz covers the APU's functions, location, self-sufficiency, and procedures during ground operations. Perfect for aviation students and professionals looking to deepen their understanding of APU systems.

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