AF Cabin Atmosphere Control Systems

Which section of a turbine engine provides high pressure bleed air to an air cycle machine for pressurization and air conditioning?

Low or high pressure compressor.
Compressor inlet.
C-D inlet compressor duct.

At which component in an air-cycle cooling system does air undergo a pressure and temperature drop?

Expansion turbine.
Primary heat exchanger.
Refrigeration bypass valve.

In a Freon vapor-cycle cooling system, where is cooling air obtained for the condenser?

Turbine engine compressor.
Ambient air.
Pressurized cabin air.

What is ventilating air used for on a combustion heater?

Provides combustion air for ground blower.
Carries heat to the places where needed.
Provides air required to support the flame.

Turbine engine air used for air conditioning and pressurization is generally called

compressed air.
ram air.
bleed air.

In the combustion heater, combustion air system, what prevents too much air from entering the heaters as air pressure increases?

Either a combustion air relief valve or a differential pressure regulator.
Only a differential pressure regulator can be used.
Only a combustion air relief valve can be used.

How is the cabin pressure of an aircraft maintained in flight?

By controlling the rate of the air flowing into the cabin.
By inflating the door seals and recirculating the conditioned cabin air.
By controlling the rate of the air flowing out of the cabin.

What controls the operation of the cabin pressure regulator?

Cabin altitude.
Bleed air pressure.
Compression air pressure.

The purpose of the dump valve in a pressurized aircraft is to relieve

all positive pressure from the cabin.
a negative pressure differential.
pressure in excess of the maximum differential.

What component might possibly be damaged if liquid refrigerant is introduced into the low side of a vapor-cycle cooling system when the pressure is too high or the outside air temperature is too low?

Compressor.
Condenser.
Evaporator.

How can it be determined that a vapor-cycle cooling system is charged with the proper amount of Freon?

Air bubbles in the sight glass disappear.
The compressor loads up and RPM decreases.
Air bubbles appear in the sight glass.

When charging a vapor-cycle cooling system after evacuation, the low-pressure gauge fails to come out of a vacuum. What is indicated?

Blockage in the system.
The expansion valve failed to close.
The compressor is not engaging.

The basic air-cycle cooling system consists of

a source of compressed air, heat exchangers, and a turbine.
heaters, coolers, and compressors.
ram air source,, compressors, and engine bleeds.

What component in a vapor-cycle cooling system would most likely be at fault if a system would not take a Freon charge?

Expansion valve.
Condenser.
Receiver-dryer.

Frost or ice buildup on a vapor-cycle cooling system evaporator would most likely be caused by

the mixing valve sticking closed.
moisture in the evaporator.
inadequate airflow through the evaporator.

What test is used to determine the serviceability of an oxygen cylinder?

Pressure test with manometer.
Pressure test with nitrogen.
Pressure test with water.

How often should standard weight high-pressure oxygen cylinders be hydrostatically tested?

Every 5 years.
Every 4 years.
Every 3 years.

To be eligible for recharging, a DOT 3HT oxygen cylinder must have been hydrostatically tested every three years and be retired from service after

24 years or 4,380 filling cycles.
15 years or 10,000 filling cycles.
10 years or 5,000 filling cycles.

Which oxygen system employs a regulator that operates only when the user inhales?

Continuous-flow system.
Emergency-flow system.
Demand-flow system.

The component that determines the pressure level in the cabin is the cabin air pressure

shut-off valve.
safety valve.
outflow valve.

Hot compressor bleed air operates the conditioned air system on some turbine aircraft, cold air supplied by the

hot air mixing valve.
vapor cycle air conditioning.
air cycle air conditioning.

For use in pressurized aircraft, which is generally the least complicated and requires the least maintenance?

Chemical oxygen generator systems.
High-pressure oxygen systems.
Low-pressure oxygen systems.

What is the main cause of contamination in a gaseous oxygen system?

Moisture.
Dust.
Nitrogen.

Where does the last stage of cooling in an air-cycle air conditioning system occur?

Refrigeration unit compressor.
Secondary heat exchanger.
Expansion turbine.

The point at which Freon flowing through a vapor-cycle cooling system gives up heat and changes from a gas to a liquid is the

condenser.
evaporator.
expansion valve.

The point at which Freon flowing through a vapor-cycle cooling system absorbs heat and changes from a liquid to a gas is the

condenser.
evaporator.
expansion valve.

How is the cabin pressure of a pressurized aircraft usually controlled?

By a pressure-sensitive switch that causes the pressurization pump to turn on or off as required.
By an autoatic outflow valve that dumps all the pressure in excess of the amount for which it is set.
By a pressure-sensitive valve that controls the output pressure of the pressurization pump.

Which is considered a good practice concerning the inspection of heating and exhaust systems of aircraft utilizing a jacket around the engine exhaust as a heat source?

Supplement physical inspections with periodic operational carbon monoxide detection tests.
All exhaust system components should be removed periodically, and their condition determined by the magnetic-particle inspection method.
All exhaust system components should be removed and replaced at each 100-hour inspection period.

On some cabin pressurization systems, pressurization on the ground is restricted by the

main landing gear operated switch.
cabin pressure regulator.
negative pressure-relief valve.

The cabin pressure control setting has a direct influence upon the

outflow valve opening.
pneumatic system pressure.
inflow valve opening.

The function of the evaporator in a Freon cooling system is to

liquefy Freon in the line between the compressor and the condenser.
lower the temperature of the cabin air.
transfer heat from the Freon gas to ambient air.

What is the purpose of a mixing valve in a compressor bleed air conditioning system?

Control the supply of hot, cool, and cold air.
Distribute conditioned air evenly to all parts of the cabin.
Combine ram air with conditioned air.

What component of a pressurization system prevents the cabin altitude from becoming higher than airplane altitude.

Cabin rate-of-descent control.
Negative pressure relief valve.
Positive pressure relief valve.

If the liquid level gauge in a vapor-cycle cooling system indicates a low Freon charge, the system should

be operated and a pressure check performed.
be operated for a period of time to reach a stable condition and then the Freon level rechecked.
not be operated until Freon and oil have been added.

If the cabin rate of climb is too great, the control should be adjusted to cause the

outflow valve to close slower.
outflow valve to close faster.
cabin compressor speed to decrease.

The position of the thermostatic expansion valve in a vapor-cycle system is determined by temperature and pressure of the

Freon entering the evaporator.
air in the outlet of the condenser.
Freon in the outlet of the evaporator.

The function of the condenser n a Freon cooling system is to

transfer heat from the Freon gas to ambient air.
change liquid Freon into a gas before it enters the compressor.
transfer heat from the cabin air to the liquid Freon.

The function of an expansion valve in a Freon cooling system is to act as a metering device and to

reduce the pressure of the gaseous Freon.
incrase the pressure of the liquid Freon.
reduce the pressure of the liquid Freon.

Which prevents a sudden loss of pressurization in the event that there is a loss of the pressurization source?

Firewall shutoff valve.
Cabin pressure outflow valve.
Delivery air duct check valve.

When servicing an air conditioning system that has lost all of its Freon, it is necessary to

check oil and add as necessary, evacuate the system, relieve vacuum, and add Freon.
check oil and add as necessary, evacuate the system, and add Freon.
check oil and add as necessary, and add Freon.

The primary function of the cabin pressurization system outflow valve is to

provide protection against overpressurization.
maintain the desired cabin pressure.
maintain the same cabin air pressure at all altitudes.

One purpose of a jet pump in a pressurization and air conditioning system is to

produce a high pressure for operation of the outflow valve.
provide for augmentation of airflow to some areas of the aircraft.
assist in the circulation of Freon.

After cleaning or replacing the filtering element in a combustion heater fuel system, the system should be pressurized and

all connections checked for leaks.
the fuel filter bypass valve reset to the filter position.
a sample of fuel taken downstream from the filter to ensure proper operation of the new filtering element.

The operation of an aircraft combustion heater is usually controlled by a thermostat circuit which

alternately turns the fuel on and off, a process known as cycling.
meters the amount of fuel continuously entering the heater and therefore regulates the heater’s BTU output.
regulates the voltage applied to the heater’s ignition transformer.

The air-cycle cooling system produces cold air by

extracting heat energy across a compressor.
passing air through cooling coils that contain a refrigerant.
extracting heat energy across an expansion turbine.

Refer to Figure 13. Determine what unit is located immediately downstream of the expansion valve in a Freon refrigeration system.

Condenser.
Compressor.
Evaporator coils.

What does a steady stream of bubbles indicate when servicing a vapor cycle air conditioning system?

The system is over charged.
The system is properly charged.
The system is under charged.

An aircraft pressurization cycle is normally considered to be

one complete series of events or operations that recur regularly.
one take off and one landing.
when the fuselage reaches its maximum pressure differential one time.

Which best describes cabin differential pressure?

Difference between cabin flight altitude pressure and mean sea level pressure.
Difference between the ambient and internal air pressure.
Difference between cabin pressure controller setting and actual cabin pressure.

Composite oxygen bottles that conform to DOT-E-8162 have a service life of

5 years or 5,000 filling cycles whichever occurs first.
10 years or 5,000 filling cycles which ever occurs first.
15 years or 10,000 filling cycles whichever occurs first.

The cabin pressurization modes of operation are

isobaric, differential, and maximum differential.
differential, unpressurized, and isobaric.
ambient, unpressurized, and isobaric.

A pressurization controller uses

bleed air pressure, outside air temperature, and cabin rate of climb.
barometric pressure, cabin altitude, and cabin rate of change.
cabin rate of climb, bleed air volume, and cabin pressure.

What unit in a vapor-cycle cooling system serves as a reservoir for the refrigerant?

Receiver-dryer.
Evaporator.
Condenser.

What is the condition of the refrigerant as it enters the condenser of a vapor-cycle cooling system?

High-pressure liquid.
Low-pressure liquid.
High-pressure vapor.

What is the condition of the refrigerant as it enters the evaporator of a vapor-cycle cooling system?

High-pressure liquid.
Low-pressure liquid.
High-pressure vapor.

The evacuation of a vapor-cycle cooling system removes any water that may be present by

drawing out the liquid.
raising the boiling point of the water and drawing out the vapor.
lowering the boiling point of the water and drawing out the vapor.

What is the condition of the refrigerant as it leaves the evaporator of a vapor-cycle cooling system?

Low-pressure liquid.
Low-pressure vapor.
High-pressure vapor.

What is the condition of the refrigerant as it leaves the condenser of a vapor-cycle cooling system?

Low-pressure liquid.
High-pressure iquid.
High-pressure vapor.

In what position should the bottle be placed when adding liquid Freon to a vapor-cycle cooling system?

Vertical with the outlet at the top.
Horizontal with the outlet to the side.
Vertical with the outlet at the bottom.

When purging a Freon air conditioning system, it is important to release the charge at a slow rate. What is the reason for the slow-rate discharge?

Prevent the large amount of Freon from contaminating the surrounding atmosphere.
Prevent excessive loss of refrigerant oil.
Prevent condensation from forming and contaminating the system.

When a vapor-cycle cooling system is not in operation, what is an indication that the system is leaking Freon?

Oil seepage.
Bubbles in the sight glass.
An ozone-like odor in the immediate area.

In an operating vapor-cycle cooling system, if the two lines connected to the expansion valve are essentially the same temperature, what does this indicate?

The system is functioning normally.
The expansion valve is not metering Freon properly.
The compressor is pumping too much refrigerant.

The purpose of a subcooler in a vapor-cycle cooling system is to

augment the cooling capacity during period of peak demand.
aid in quick cooling a hot aircraft interior.
cool the Freon to prevent premature vaporization.

A small amount of water in a vapor-cycle cooling system can freeze

In the receiver-dryer and stop the entire system operation.
in the expansion valve and stop the entire system operation.
but the system is designed to continue operation.

When Refrigerant-12 is passed over an open flame, it

changes to methane gas.
is broken down into its basic chemical elements.
changes to phosgene gas.

What type of oil is suitable for use in a vapor-cycle cooling system?

Low viscosity engine oil with the inability to absorb water.
Special high grade refrigeration oil.
Highly refined synthetic oil, free from impurities with special water absorbing additives.

When an aircraft’s oxygen system has developed a leak, the lines and fittings should be

removed and replaced.
inspected using a special oxygen system dye penetrant.
bubble tested with a special soap solution manufactured specifically for this purpose.

If oxygen bottle pressure is allowed to drop below a specified minimum, it may cause

the pressure reducer to fail.
the automatic altitude control valve to open.
moisture to collect in the bottle.

What controls the amount of oxygen delivered to a mask in a continuous-flow oxygen system?

Calibrated orifice.
Pressure reducing valve.
Pilot’s regulator.

When does the diluter-demand regulator operate?

When the user selects alternate oxygen.
When the user selects 100 percent oxygen.
When the user inhales.

The primary difference between aviation breathing oxygen and other types of commercially available compressed oxygen is that

the other types are usually somewhat less than 99.5% pure oxygen.
aviation breathing oxygen has had all the water vapor removed.
aviation breathing oxygen has a higher percentage of water vapor to help prevent drying of a person’s breathing passages and possible dehydration.

What is used in some oxygen systems to change high cylinder pressure to low system pressure?

Pressure reducer valve.
Calibrated fixed orifice.
Diluter demand regulator.

In a high-pressure oxygen system, if the pressure reducer fails, what prevents high-pressure oxygen from entering the system downstream?

Check valve.
Pressure relief valve.
Manifold control valve.

High-pressure cylinders containing oxygen for aviation use can be identified by their

green color and the words BREATHING OXYGEN stenciled in 1-inch white letters.
yellow color and the words AVIATOR’S BREATHING OXYGEN stenciled in 1-inch white letters.
green color and the words AVIATOR’S BREATHING OXYGEN stenciled in 1-inch white letters.

Refer to Figure 14. One hour after an oxygen system was charged for a leakage check, the oxygen pressure gauge read 460 psi at 63 degrees F; 6 hours later the temperature was 51 degrees F. (A 5 psi change is the maximum allowable in a 6-hour period.) What pressure gauge reading would be acceptable to remain within the allowable limits?

445 to 450 psi.
446 to 450 psi.
455 to 460 psi.

An aircraft oxygen bottle may be considered airworthy if it has been hydrostatically tested and identified

with the test date, DOT number, and serial number stamped on the cylinder near the neck.
with the DOT number, serial number, and manufacturer stamped on the cylinder near the neck.
with the DOT number and manufacturer stamped on the cylinder near the neck.

In a gaseous oxygen system, which of the following are vented to blow out plugs in the fuselage skin?

Pressure relief valves.
Filler shutoff valves.
Pressure reducer valves.

What is the purpose of pressurizing the aircraft cabin?

To permit the aircraft to operate in thunderstorms.
To allow aircraft systems to operate properly.
To make human flight possible in the hostile environment of the upper atmosphere.

Oxygen systems in unpressurized aircraft are generally of the

continuous-flow and pressure-demand types.
pressure-demand type only.
portable-bottle type only.

The purpose of the airflow metering aneroid assembly found in oxygen diluter demand regulators is to

regulate airflow in relation to oxygen flow when operating in emergency or diluter demand positions.
regulate airflow in relation to cabin altitude when in diluter demand position.
automatically put the regulator in emergency position if the demand valve diaphragm ruptures.

If a high-pressure oxygen cylinder is to be installed in an airplane, it must meet the specifications of the

aircraft manufacturer or the cylinder manufacturer.
Department of Transportation.
National Transportation Safety Board or the Standards of Compressed Gas Cylinders.

Before a high-pressure oxygen cylinder is serviced, it must be the correct type and have been

hydrostatically tested within the proper time interval.
approved by the National Transportation Safety Board.
Inspected by a certificated airframe mechanic.

A contaminated oxygen system is normally purged with

oxygen.
compressed air.
nitrogen.

How should you determine the amount of oxygen in a portable, high-pressure cylinder?

Weigh the cylinder and its contents.
Read the pressure gauge mounted on the cylinder.
Measure the pressure at the mask.

What may be used as a lubricant on oxygen system tapered pipe thread connections?

Silicone dielectric compound.
Glycerine.
Teflon tape.

On transport category aircraft what might be an indication of an over pressure event of the aircraft oxygen system?

The green thermal expansion disk missing.
The green thermal expansion disk in the cockpit missing.
The green thermal expansion disk on the oxygen regulator missing.

Which of the following are characteristic of a chemical or solid-state oxygen system?

A volume storage capacity about three times that of compressed oxygen and system generators that are inert below 400 degrees F, even under severe impact.
An adjustable oxygen release rate and a volume storage capacity about three times that of compressed oxygen.
System generators are inert below 400 degrees F, even under severe impact, and a distribution and regulating system similar to gaseous oxygen systems.

Oxygen used in aircraft systems

is at least 99.5% pure and is practically water free.
is at least 99.5% pure and is the same as hospital-quality oxygen.
contains a higher level of water vapor than hospital-quality oxygen.

AF Cabin Atmosphere Control Systems

Jon K

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