Aircraft Auxiliary Power Unit (APU) Systems

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What is the primary source of fuel for an APU?

Ground power source

Portable power source

Electric power source

Aircraft fuel tanks (correct)

How does an APU respond to changes in electrical or pneumatic load demands?

It shuts down to prevent overheating

It runs at a constant speed regardless of the load (correct)

It decreases its speed to conserve fuel

It increases its speed to meet the demand

What is the purpose of the fuel bypass in an APU system?

To bypass excess fuel to prevent over-fuelling (correct)

To cool the APU

To prevent fuel pump overheating

To supply fuel to the main engines

What type of control system are modern APUs typically equipped with?

Electronic Signup and view all the answers

What provides power to the APU for start-up?

The APU itself Signup and view all the answers

What is the primary function of an APU?

To provide electric power and cooling Signup and view all the answers

What is a key feature of an APU's design?

Constant speed Signup and view all the answers

What is a safety feature of an APU?

Fire protection system Signup and view all the answers

During an actual fire warning, when does the APU automatically shut down in later model Boeing and Airbus aircraft?

When the aircraft is on the ground Signup and view all the answers

What is the purpose of running an APU fire test before starting the APU?

To check the integrity of the APU fire-detecting circuitry and extinguisher Signup and view all the answers

Why is it important to monitor the APU with trained personnel and firefighting equipment when running it with the cowlings open?

Because it compromises the fire-sensing and extinguishing capabilities Signup and view all the answers

What is the purpose of an APU ground run?

To verify the normal operation and condition of the APU Signup and view all the answers

What is the primary function of the ECB in relation to the engine?

To monitor and control the engine's starting sequence Signup and view all the answers

What is the APU compartment constructed to do?

To minimize the possibility of fire Signup and view all the answers

What is the purpose of the ECB's BITE capability?

To shorten diagnostic operations during troubleshooting and maintenance Signup and view all the answers

In later model Boeing and Airbus aircraft, who is responsible for shutting down the APU during an actual fire warning when the aircraft is in the air?

The pilot Signup and view all the answers

What happens when the APU master switch is selected to ON?

Power is supplied to the APU control box and the APU air intake door opens Signup and view all the answers

What is the purpose of the fire-detection circuitry and dedicated fire extinguisher in the APU compartment?

To detect and extinguish fires Signup and view all the answers

What is the function of the electronic speed-sensing unit?

To monitor and control the engine's starting sequence Signup and view all the answers

Why is it necessary to monitor the APU with trained personnel and firefighting equipment during ground tests?

Because it compromises the fire-sensing and extinguishing capabilities Signup and view all the answers

What happens when the start button is pressed?

The start control relay is energized and remains energized Signup and view all the answers

What is stored in the ECB for later interrogation?

Fault information and LRU failures Signup and view all the answers

What is the purpose of the cockpit fault display?

To provide diagnostic information from the central maintenance computer interface Signup and view all the answers

What is the role of the ECB in relation to the LRUs?

To monitor the LRUs for faults Signup and view all the answers

What is recorded on the data plate?

Engine condition during part power trimming Signup and view all the answers

What is the purpose of the data plate speed check?

To ensure the engine is running within specified tolerances Signup and view all the answers

What is the benefit of trend monitoring?

Reducing aircraft downtime Signup and view all the answers

What are the two paths of conventional trend monitoring?

Mechanical and performance parameters Signup and view all the answers

What is engine trend monitoring based on?

Consistency with corrected performance figures Signup and view all the answers

What is the purpose of correcting the observed N2 tachometer indication?

To account for temperature variation from 59 °F Signup and view all the answers

What is the result of a variation outside manufacturer specified tolerances?

The FCU needs adjustment or the engine is worn Signup and view all the answers

What is the result of advances in microprocessor-aided monitoring?

More information available to the aircrew and maintenance crew Signup and view all the answers

What is a potential consequence of reinstalling accessories incorrectly after an engine overhaul?

Engine malfunction or irreparable damage Signup and view all the answers

Why should you refer to the accessory records before de-preservation?

To determine how long the engine and accessories have been in storage Signup and view all the answers

What should you check for during a visual inspection of a replacement accessory?

Signs of corrosion and freedom of operation Signup and view all the answers

Why is it essential to lubricate the accessory drive shaft?

To ensure smooth operation and prevent damage Signup and view all the answers

What should you remove before installing a replacement accessory?

Plastic plugs and movement restraints Signup and view all the answers

Why are new O-rings or gaskets necessary during accessory installation?

To ensure a secure seal between the mounting pad and accessory Signup and view all the answers

What should you do before de-preserving any accessories enclosed with the engine?

Refer to the accessory records Signup and view all the answers

What is the purpose of cleaning the mounting pad and flange during accessory installation?

To ensure a secure seal Signup and view all the answers