Questions and Answers - Aircraft Cabin Environmental

Study Aid Questions

Fill in the Blanks

1. Oxygen is a _________________________, __________________________, and _________________________ gas at normal atmospheric temperatures and pressures.

2. The words ____________________________________________ should be marked clearly on any cylinder containing oxygen for aircraft use.

3. Oxygen cylinders are considered empty when the pressure inside drops below _______________ psi. This ensures that air containing ___________________________________ has not entered the cylinder.

4. When oxygen is delivered only as the user inhales, it is known as a ______________________________ system.

5. There are two types of individual oxygen demand regulators: they are:
_____________________________________________ _____________________________________________

6. The main cause of contamination in an oxygen system is _______________________________________.

7. The cabin pressurization system must be capable of maintaining a cabin pressure attitude of _______________. or lower regardless of _______________________________.

8. Metal fatigue from repeated ___________________________, and ____________________________ weakens the aircraft structure.

9. There are three typical sources of air used to pressurize reciprocating aircraft. They are:
______________________________ ______________________________ ______________________________

10. Aircraft equipped with turbine engines typically use ______________________________________ as a source for cabin pressurization.

11. Aircraft cabin pressurization systems work in two different modes of operation. They are:
_____________________________________________ ______________________________________________

12. The flight crew can select and control _____________________________, ____________________________, and ____________________________________ on the cabin pressure controller.

13. The cabin pressure controller controls the position of the ___________________________________ located normally at the rear of the aircraft.

14. Many transport category aircraft have an outflow valve that operates ___________________________ , using signals sent from a remotely located ________________________________ that act as the pressure regulator.

15. Pressurization safety relieve valves are used to prevent __________________________________ of the cabin.

16. ____________________________________ are used to ensure that air pressure outside the aircraft does not exceed cabin air pressure.

17. Aircraft with reciprocating engines often use a _________________________ cooling system, and turbine powered aircraft use a __________________________ cooling system.

18. The air cycle cooling system is supplied with air from either ___________________________ or ____________

19. The heart of the air cycle cooling system is the _______________________________________, also known as the ________________________________________

20. The duct temperature sensors used in the temperature control system are ____________________________. Their ______________________________________ changes as temperature changes.

21. The temperature at which a substance changes from a _____________________ into a ___________________ when heat is added is known as the boiling point.

22. R134a refrigerant is filtered and stored under pressure in a reservoir known as __________________________

23. Most evaporators are constructed of ___________________________ or _____________________________ tubing coiled into a compact unit.

24. A concern of exhaust shroud heat system is that __________________________ could contaminate the cabin.

25. Maintenance of combustion heaters consists of routine items such as _________________________, checking ____________________________________ wear, and ensuring inlets are not plugged.


1. Gaseous oxygen systems are used in commercial aircraft and LOX oxygen systems are primarily used in military aircraft. TRUE/FALSE

2. Most oxygen storage cylinders are painted blue, but yellow and white may be used as well. TRUE/FALSE

3. Demand‐flow systems are used most frequently by the crew on high performance and air transport category aircraft. TRUE/FALSE

4. A blown out green disk in the side of fuselage indicates that the oxygen supply is low and this should be investigated before flight. TRUE/FALSE

5. The solid chemical oxygen generators used in most airliners are activated automatically by depressurization or manually by a switch operated by the flight crew. TRUE/FALSE

6. Petroleum products such as grease and oil should never be used for oxygen system maintenance because an explosion could be the result. TRUE/FALSE

7. The cabin pressurization system must maintain the cabin pressure altitude below 10,000 ft. TRUE/FALSE

8. Metal fatigue can result from repeated pressurization cycles and can weaken the airframe structure. TRUE/FALSE

9. Superchargers are the common source of pressurization on modern reciprocating engine aircraft. TRUE/FALSE

10. Turbochargers are driven by a shaft or a drive belt. TRUE/FALSE

11. Large turbine powered aircraft use bleed air from the engine compressor section as a source of air for cabin pressurization. TRUE/FALSE

12. The isobaric control mode of a cabin pressurization system controls cabin pressure to maintain a constant pressure between the air pressure outside the cabin and the ambient air pressure. TRUE/FALSE

13. Small aircraft often use a pneumatically controlled outflow valve while transport category aircraft use electrically/electronically controlled outflow valves. TRUE/FALSE

14. Pressurization safety relieve valves are used to prevent negative cabin pressure. TRUE/FALSE

15. Many pack valves used in air conditioning systems are electrically controlled and pneumatically operated. TRUE/FALSE

16. The primary heat exchanger is cooled by an electric fan during stationary ground operations and ram air is used in flight. TRUE/FALSE

17. The water separator has a fiberglass bag (sock) that condenses and coalesces the mist into larger water droplets. Gravity will drain the water droplets from the water separator. TRUE/FALSE

18. The function of the refrigeration by‐pass valve is to regulate the temperature of the air cycle machine so it does not freeze when passing through the water separator. TRUE/FALSE

19. A vapor cycle air conditioning system is an open system in which a refrigerant is circulated through tubing and a variety of components. TRUE/FALSE

20. Most modern vapor cycle cooling systems on aircraft use R12 refrigerant which has replaced the R134a refrigerant. TRUE/FALSE

21. During a feel test components and lines in the high side (from the compressor to the expansion valve) should warm or hot to the touch. TRUE/FALSE

22. During a feel test low side lines and the evaporator should be warm. TRUE/FALSE

23. The charging capacity of a vapor cycle air conditioning system is measured by weight. TRUE/FALSE

24. Most single‐engine light aircraft use a bleed air system to heat the cabin. TRUE/FALSE

25. The fuel for the combustion heater is drawn from a dedicated small fuel tank inside the cabin. TRUE/FALSE

Knowledge Application Questions

1. What component in the pressurization system is the principal control of a pressurization system?

2. What source of air supply is used by most turbine‐powered aircraft for pressurization?

3. What pressurization control unit will change the position of an outflow valve?

4. On reciprocating engine aircraft, what are some methods of supplying heat to the cabin?

5. What is the function of ventilating air in a combustion heater?

6. What are the typical components used in an air‐cycle cooling system?

7. What causes a temperature drop in an air‐cycle cooling system?

8. Describe how a water separator in an air cycle cooling system removes moisture from the air?

9. Describe the theory of operation of a vapor‐cycle cooling system illustrated in textbook figure 16‐74?

10. Describe the theory of operation of an air cycle cooling system illustrated in textbook figure 16‐63.

11. What are the main components in a vapor‐cycle cooling system?

12. How does a continuous‐flow oxygen system operate?

13. What must be accomplished if an oxygen system has been open to atmosphere for 2 hours or more?

14. What is used to purge oxygen lines of moisture?

15. What type of oxygen must be used in aircraft?

16 Why is oil added to a vapor‐cycle Freon system?

17. What safety precautions should be observed when servicing oxygen systems?

18. What sources of air are used by pressurized aircraft with a reciprocating engine?

19. What is the main advantage of using LOX systems?

20. What kind of adjustments can be made on a pressure controller?

Multiple Choices Questions

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

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

2. The basic air cycle cooling system consists of:

a. a source of compressed air, heat exchangers, and an air cycle machine
b. heaters, coolers, and compressors
c. ram air source, compressors, and engine bleeds

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

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

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

a. Turbine engine compressor
b. Ambient air
c. Pressurized cabin air

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

a. Expansion valve
b. Condenser
c. Receiver dryer

6. What controls the operation of the cabin pressure regulator?

a. Cabin altitude
b. Bleed air pressure
c. Compression air pressure

7. The cabin pressure of an aircraft in flight is maintained at the selected altitude by

a. controlling the air inflow rate
b. inflating door seals and recirculating conditioned cabin air
c. controlling the rate at which air leaves the cabin

8. What is ventilating air used for on a combustion heater?

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

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

a. Expansion turbine
b. Primary heat exchanger
c. Refrigeration bypass valve

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

a. Every 5 years
b. Every 4 years
c. Every 3 years

11. Turbine engine air used for air conditioning and pressurization is generally called:

a. compressed air
b. ram air
c. bleed air

12. 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?

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

13. In the diluter demand oxygen regulator, when does the demand valve operate?

a. When the diluter control is set at normal
b. When the user demands 100 percent oxygen
c. When the user breathes

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

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

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

a. Check valve
b. Pressure relief valve
c. Manifold control valve

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

a. Low pressure liquid
b. High pressure liquid
c. High pressure vapor

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

a. Low pressure liquid
b. Low pressure vapor
c. High pressure vapor

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

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

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

a. Pressure relief valves
b. Filler shutoff valves
c. Pressure reducer valves

20. High pressure cylinders containing oxygen for aviation use can be identified by their:

a. green color and the words 'BREATHING OXYGEN' stenciled in 1‐inch white letters
b. yellow color and the words 'AVIATOR'S BREATHING OXYGEN' stenciled in 1‐inch white letters
c. green color and the words 'AVIATOR'S BREATHING OXYGEN' stenciled in 1‐inch white letters

21. What part of a pressurization system prevents cabin altitude from becoming higher than airplane altitude?

a. Cabin rate of descent control
b. Negative pressure relief valve
c. Positive pressure relief valve

22. The cabin pressure control setting has a direct influence upon the:

a. outflow valve opening
b. pneumatic system pressure
c. inflow valve opening

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

a. outflow valve to close slower
b. outflow valve to close faster
c. cabin compressor speed to decrease

24. The main cause of contamination in gaseous oxygen systems is:

a. moisture
b. dust and other airborne particulates
c. other atmospheric gases

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

a. Silicone dielectric compound
b. Glycerin
c. Teflon tape

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

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

27. What unit in a vapor cycle cooling system serves as a reservoir for the refrigerant?
a. Receiver dryer
b. Evaporator
c. Condenser

28. Which best describes cabin differential pressure?
a. Difference between cabin flight altitude pressure and Mean Sea Level pressure
b. Difference between the ambient and internal air pressure
c. Difference between cabin pressure controller setting and actual cabin pressure

29. Regarding the statements below:

(1) Usually bleed air from a gas‐turbine engine compressor can be safely used for cabin pressurization.

(2) Independent cabin condition air machines (air cycle machine) can be powered by bleed air from an aircraft turbine engine compressor.

a. only No. 1 is true
b. only No. 2 is true
c. both No. 1 and No. 2 are true

30. The cabin pressurization modes of operation are:

a. isobaric, differential, and maximum differential
b. differential, unpressurized, and isobaric
c. ambient, unpressurized, and isobaric

Physiology of Flight
Aircraft Oxygen Systems
Oxygen Systems and Components
Oxygen System Servicing
Prevention of Oxygen Fires or Explosions
Aircraft Heaters
Aircraft Pressurization Systems
Pressurization Issues
Sources of Pressurized Air
Control of Cabin Pressure
Pressurized Aircraft
Air Conditioning Systems
Vapor Cycle Air Conditioning System Servicing
Vapor Cycle Air Conditioning System Components
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