AIRCON + PRESSURISATION CONTD

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Questions and Answers

What is the correct differential pressure for the cabin compared to the discharge valve?

Negative differential pressure

Lower differential pressure than the discharge valve

Equal differential pressure to the discharge valve

Higher differential pressure than the discharge valve (correct)

What is the main purpose of the cabin pressurization system?

To maintain a constant cabin altitude

To adjust the temperature and pressure in the cabin (correct)

To add oxygen to the cabin

To remove moisture from the cabin

What is the principle of cabin pressurization?

The cabin altitude is maintained at a constant level regardless of aircraft altitude

The cabin climbs to a lower altitude than the aircraft as it climbs (correct)

The cabin altitude maintains a constant differential to the aircraft altitude

The cabin altitude eventually climbs to the same altitude as the aircraft

What is the function of the mass airflow control valve?

To maintain a reasonable mass flow of air into the cabin regardless of aircraft altitude Signup and view all the answers

How does the cabin pressure controller maintain a pre-set cabin altitude?

By regulating the position of the outflow valve Signup and view all the answers

What happens if the cabin height is set lower than the airfield height with the squat switches overridden?

The outflow valve will remain closed Signup and view all the answers

Which of the following sometimes inhibits an air conditioning pack?

Throttle switches Signup and view all the answers

What should be used when carrying out a ground pressure test?

The aircraft engines to test the whole system Signup and view all the answers

What is the minimum required humidity for the ventilation air in the aircraft cabin?

30 percent Signup and view all the answers

In a Bootstrap Air Conditioning supply system, the source of compressed air is from where?

Gas turbine compressor bleed air Signup and view all the answers

What is the cabin differential pressure?

the difference between cabin pressure and atmospheric pressure Signup and view all the answers

What regulates the outflow of air from the cabin?

the outflow valves Signup and view all the answers

When air is pressurized, what happens to the oxygen content?

it increases Signup and view all the answers

What is the difference that cabin pressure differential refers to?

cabin pressure and ambient pressure Signup and view all the answers

In a 'bootstrap' cooling system, what is the first step in the air supply process?

compressed then passed through a heat exchanger and across an expansion turbine Signup and view all the answers

If an altitude of 8000 feet is selected on the cabin pressure controller, what will happen?

8000 feet cabin conditions will be maintained at aircraft altitudes above 8000 feet Signup and view all the answers

If cabin pressure is increasing, what will the cabin rate of change indicator show?

a rate of descent Signup and view all the answers

What prevents a negative differential pressure?

an inward relief valve Signup and view all the answers

During a normal climb from aerodrome level with the pressurization system 'ON', what happens?

the atmospheric pressure decreases more quickly than the cabin pressure Signup and view all the answers

At what cabin differential is the inward relief valve usually set to operate?

-0.5 PSI Signup and view all the answers

In a pressurized aircraft, why are inward relief valves interconnected?

To allow controlled pressure during descent Signup and view all the answers

Why is a cabin pressure air leak from the front of the fuselage considered most undesirable?

Because of the drag created Signup and view all the answers

What is the purpose of loading the inward relief valve spring in a closed position?

To prevent air leaks Signup and view all the answers

What type of air system is used in a turbo fan cold air system for cooling?

Ram air from ambient conditions Signup and view all the answers

When a 'muff' or air ducting is built around the engine exhaust system and air is directed around inside the muffler, this acts as an:

Exhaust heater Signup and view all the answers

Where does the heat exchanger cooling air in a turbo fan cold air system come from?

From ambient conditions through ram air Signup and view all the answers

What is the cabin pressure equivalent to while in flight?

The cabin pressure is equivalent to an altitude of less than 10,000 ft Signup and view all the answers

What does the pressure controller activate?

The cabin discharge valve Signup and view all the answers

Why is the flight altitude set on the pressurization control panel higher than the actual flight altitude when cruising near the operational ceiling?

To prevent pressure controller hunting Signup and view all the answers

How is the cabin rate of climb shown?

On a specific indicator Signup and view all the answers

What is the purpose of a water separator in a pressurization system?

To extract surplus water from the charge air Signup and view all the answers

Where does the supply air flow to after passing through the primary heat exchanger in a turbo-fan cold air system?

The fan Signup and view all the answers

How is the heat exchanger in a turbo-fan system cooled?

By ambient ram air Signup and view all the answers

What factors determine the effective temperature of a cabin?

Temperature and humidity Signup and view all the answers

What is the purpose of an inward relief valve in a pressurization system?

To ensure the pressure hull is not subjected to a high negative differential pressure Signup and view all the answers

How does the amount of compressed air delivered to the cabin vary with altitude in most pressurization systems?

It is reasonably constant irrespective of altitude Signup and view all the answers

What type of markings are used for air conditioning pipelines?

Dots Signup and view all the answers

How does the cabin pressure controller maintain cabin altitude?

By controlling the outflow valve position Signup and view all the answers

When is a cabin humidifier typically operated?

At high altitudes Signup and view all the answers

How is heat added to the air in an air conditioning system?

By restricting the compressor outlet Signup and view all the answers

What is the purpose of the ditching control?

To close all valves and inlets Signup and view all the answers

What is the function of the mass flow controller?

To ensure a constant mass of air is delivered to the cabin Signup and view all the answers

What controls the rate of change of cabin pressure in an aircraft?

The pressure controller, as selected by the pilot Signup and view all the answers

If an aircraft has a maximum differential pressure of 8.5 PSI at cruising altitude, and the ambient pressure is 2.9 PSI, what would be the pressure inside the cabin?

11.4 PSI Signup and view all the answers

Before filling a vapor cycle cooling system, what should be done?

Apply suction to remove air and moisture Signup and view all the answers

What determines the cabin differential pressure in an aircraft?

Both the height at which the aircraft is flying and the selected cabin height Signup and view all the answers

What is the minimum rate of flow of air from the punkha louvers (vents) in an aircraft cabin?

25 ft/min Signup and view all the answers

What is the primary reason for air conditioning and pressurizing an aircraft cabin?

To maintain human efficiency and comfort during flights at high altitudes Signup and view all the answers

If the pilot selects a cabin height of 8000 ft while taxiing and activates the pressurization system, what will happen to the cabin pressure?

Remain at ground level pressure Signup and view all the answers

What is the purpose of a silencer in a pressurization system?

To reduce the noise from the blowers and/or compressors in the system Signup and view all the answers

When should the rate of change of pressure be particularly low to avoid discomfort?

During descent Signup and view all the answers

In a vapor cycle cooling system, how is heat removed from the charge air?

By changing a liquid into a vapor Signup and view all the answers

Study Notes

Cabin Pressure and Air Conditioning Systems

Inward relief valve is spring-loaded to the closed position.
A cabin pressure air leak from the front of the fuselage is most undesirable because of the drag created.
An exhaust heater is a type of heater that uses a muff or air ducting built around the engine exhaust system and directs air around the muffler.

Pressurization Systems

Inward relief valves are interconnected in pressurized aircraft to allow controlled pressure during descent.
Safety valves relieve at a specific pressure to prevent over-pressurization.
The rate of change of cabin pressure is selected by the pilot and controlled by the pressure controller.
Cabin differential pressure is the difference between cabin pressure and atmospheric pressure.
If the ambient pressure is 2.9 PSI, the pressure inside the cabin at cruising altitude would be 11.4 PSI.

Air Conditioning Systems

Before filling a vapor cycle cooling system, apply suction to remove air and moisture.
Cabin differential is determined by the height at which the aircraft is flying and the selected cabin height.
The rate of flow of air from the punkha louvers should not be less than 25 ft/min.
An aircraft cabin is air-conditioned and pressurized to maintain human efficiency and comfort during flights at high altitudes.

Air Conditioning and Pressurization Controllers

A cabin pressure controller maintains a particular cabin altitude by controlling the outflow valve position.
A silencer is installed in a pressurization system to reduce the noise from the blowers and/or compressors.
To avoid discomfort, the rate of change of pressure should be low, particularly during descent.

Vapor Cycle Cooling Systems

In a vapor cycle cooling system, heat is removed from the charge air by changing a liquid into a vapor.
An inward relief valve will operate when cabin pressure is lower than ambient pressure.
If an aircraft is operating at 40,000 ft, the pressurization ensures that the equivalent height of the aircraft above sea level is maintained.

Additional Facts

Cabin humidifiers are operated at high altitudes.
Ditching control is used for closing all valves and inlets.
The purpose of a mass flow controller is to ensure that a constant mass of air is delivered to the cabin at all times.
Failure of the normal maximum differential pressure control is catered for by cabin safety relief valves.
A turbo fan CAU used for air cycle cooling will decrease pressure and temperature of the charge air.
The cabin differential pressure is the difference between cabin pressure and atmospheric pressure.
The outflow of air from the cabin is regulated by the outflow valves.
When air is pressurized, the oxygen content increases.
Cabin pressure differential is the difference between cabin pressure and ambient pressure.
In a 'bootstrap' cooling system, the supply of air is first compressed, then passed through a heat exchanger and across an expansion turbine.### Cabin Pressurization
The cabin pressure is equivalent to an altitude of less than 10,000 ft.
The pressure controller activates the cabin discharge valve.

Pressure Controller

The pressure controller prevents pressure controller hunting by setting the flight altitude 500 ft higher than the actual flight altitude.

Cabin Rate of Climb

The cabin rate of climb is shown on a specific indicator.

Water Separator

A water separator is installed in a pressurization system to extract surplus water from the charge air.

Turbo-Fan Cold Air System

After passing through the primary heat exchanger, the supply air flows to the fan.
The heat exchanger in a turbo-fan system is cooled by ambient ram air.

Cabin Temperature

The effective temperature of a cabin is determined by temperature and humidity.

Inward Relief Valve

An inward relief valve is installed in a pressurization system to prevent a high negative differential pressure in the pressure hull of an aircraft.

Pressurization System

The amount of compressed air delivered to the cabin is reasonably constant, regardless of altitude.

Vapour Cycle System

When dissipating heat in a vapour cycle system, vapour converts to a liquid.

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Description

Test your knowledge on aircraft maintenance with questions 68 and 69. Identify the correct positions and scenarios related to relief valves and cabin pressure air leaks. No explanations provided for the answers.