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:
____________ and ____________.
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:
____________, ____________ and ____________.
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:
____________ and ____________.
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.
True or False
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)
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?
Multiple Choice Questions
1. Which section of a turbine engine provides high pressure bleed air to an air cycle machine for pressurization and air-conditioning?a. C-D inlet compressor duct.
b. Inlet compressor.
c. Turbine compressor.
2. 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.
3. In a freon vapor cycle cooling system, where is cooling air obtained for the condenser?
a. Pressurized cabin air.
b. Turbine engine compressor.
c. Ambient air.
4. What is ventilating air used for on a combustion heater?
a. Provides air required to support the flame.
b. Carries heat to the places where needed.
c. Provides combustion air for ground blower.
5. Turbine engine air used for air conditioning and pressurization is generally called
a. ram air.
b. compressed air.
c. bleed air.
6. In the combustion heater, combustion air system, what prevents too much air from entering the heaters as air pressure increases?
a. Only a differential pressure regulator can be used.
b. Either a combustion air relief valve or a differential pressure regulator.
c. Only a combustion air relief valve can be used.
7. The cabin pressure of an aircraft in flight is maintained at the selected altitude by
a. controlling the air inflow rate.
b. controlling the rate at which air leaves the cabin.
c. inflating door seals and recirculating conditioned cabin air.
8. What controls the operation of the cabin pressure regulator?
a. Cabin altitude.
b. Bleed air pressure.
c. Compression air pressure.
9. The basic air cycle cooling system consists of
a. heaters, coolers, and compressors.
b. a source of compressed air, heat exchangers, and a turbine.
c. ram air source, compressors, and engine bleeds.
10. The purpose of the dump valve in a pressurized aircraft is to relieve
a. a negative pressure differential.
b. pressure in excess of the maximum differential.
c. all positive pressure from the cabin.
11. 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?
a. Compressor.
b. Condenser.
c. Evaporator.
12. How can it be determined that a vapor cycle cooling system is charged with the proper amount of freon?
a. The compressor loads up and RPM decreases.
b. Air bubbles appear in the sight glass.
c. Air bubbles in the sight glass disappear.
13. When charging a vapor cycle cooling system after evacuation, the low pressure gauge fails to come out of a vacuum. What is indicated?
a. The expansion valve failed to close.
b. Blockage in the system.
c. The compressor is not engaging.
14. 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.
15. Frost or ice buildup on a vapor cycle cooling system evaporator would most likely be caused by
a. moisture in the evaporator.
b. the mixing valve sticking closed.
c. inadequate airflow through the evaporator.
16.. What test is used to determine the serviceability of an oxygen cylinder?
a. Pressure test with water.
b. Pressure test with nitrogen.
c. Pressure test with manometer.
17. How often should standard weight high pressure oxygen cylinders be hydrostatically tested?
a. Every 4 years.
b. Every 3 years.
c. Every 5 years.
18. To be eligible for recharging, a DOT 3HT oxygen cylinder must have been hydrostatically tested every three years and be retired from service after
a. 15 years or 10 000 filling cycles.
b. 24 years or 4380 filling cycles.
c. 10 years or 5000 filling cycles.
19. What type of oxygen system uses the rebreather bag-type mask?
a. Demand.
b. Diluter demand.
c. Continuous flow.
20. The altitude controller maintains cabin altitude by modulation of the
a. outflow valve.
b. safety valve.
c. safety and outflow valves.
21. Hot compressor bleed air operates the conditioned air system on some turbine aircraft, how is cold air supplied?
a. By the ram cycle cooling unit.
b. By the flow control unit.
c. By the air cycle machine turbine.
22. For use in pressurized aircraft, which is generally the least complicated and requires the least maintenance?
a. High-pressure oxygen systems.
b. Low-pressure oxygen systems.
c. Chemical oxygen generator systems.
23. The main cause of contamination in gaseous oxygen systems is
a. moisture.
b. dust and other airborne particulates.
c. other atmospheric gases.
24. Where does the last stage of cooling in an air cycle air conditioning system occur?
a. Secondary heat exchanger.
b. Refrigeration unit compressor.
c. Expansion turbine.
25. 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
a. expansion valve.
b. evaporator.
c. condenser.
26. The point at which freon flowing through a vapor cycle cooling system absorbs heat and changes from a liquid to a gas is the
a. condenser.
b. expansion valve.
c. evaporator.
27. How is the cabin pressure of a pressurized aircraft usually controlled?
a. By an automatic outflow valve that dumps all the pressure in excess of the amount for which it is set.
b. By a pressure sensitive valve that controls the output pressure of the pressurization pump.
c. By a pressure sensitive switch that causes the pressurization pump to turn on or off as required.
28. 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?
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.
29. On some cabin pressurization systems, pressurization on the ground is restricted by the
a. main landing gear operated switch.
b. negative pressure-relief valve.
c. cabin pressure regulator.
30. The cabin pressure control setting has a direct influence upon the
a. outflow valve opening.
b. pneumatic system pressure.
c. inflow valve opening.
31. The function of the evaporator in a freon cooling system is to
a. lower the temperature of the cabin air.
b. transfer heat from the freon gas to ambient air.
c. liquefy freon in the line between the compressor and the condenser.
32. What is the purpose of a mixing valve in a compressor bleed air air-conditioning system?
a. Distribute conditioned air evenly to all parts of the cabin.
b. Combine ram air with conditioned air.
c. Control the supply of hot, cool, and cold air.
33. What component of a pressurization system prevents the cabin altitude from becoming higher than airplane altitude?
a. Negative pressure relief valve.
b. Cabin rate of descent control.
c. Positive pressure relief valve.
34. If the liquid level gauge in a vapor cycle cooling system indicates a low freon charge, the system should
a. be operated and a pressure check performed.
b. not be operated until freon and oil have been added.
c. be operated for a period of time to reach a stable condition and then the freon level rechecked.
35. If the cabin rate of climb is too great, the control should be adjusted to cause the
a. cabin compressor speed to decrease.
b. outflow valve to close slower.
c. outflow valve to close faster.
36. The position of the thermostatic expansion valve in a vapor cycle cooling system is determined by temperature and pressure of the
a. freon entering the evaporator.
b. freon in the outlet of the evaporator.
c. air in the outlet of the condenser.
37. The function of the condenser in a freon cooling system is to
a. transfer heat from the freon gas to ambient air.
b. change liquid freon into a gas before it enters the compressor.
c. transfer heat from the cabin air to the liquid freon.
38. The function of an expansion valve in a freon cooling system is to act as a metering device and to
a. reduce the pressure of the gaseous freon.
b. increase the pressure of the liquid freon.
c. reduce the pressure of the liquid freon.
39. Which prevents a sudden loss of pressurization in the event that there is a loss of the pressurization source?
a. Firewall shutoff valve.
b. Cabin pressure outflow valve.
c. Delivery air duct check valve.
40. When servicing an air conditioning system that has lost all of its freon, it is necessary to
a. check oil and add as necessary, evacuate the system, relieve vacuum, and add freon.
b. check oil and add as necessary, evacuate the system, and add freon
c. check oil and add as necessary, and add freon.
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Answers
Fill in the Blanks1. Colorless, odorless, tasteless
2. Aviator Breathing Oxygen
3. 50, water vapor
4. Demand‐flow
5. Diluter‐demand, pressure‐demand
6. Moisture
7. 8,000 ft, cruising altitude
8. Pressurization, depressurization
9. Supercharger, turbocharger, engine driven compressor
10. Bleed air
11. Isobaric, differential
12. Cabin altitude, rate of change, barometric pressure
13. Outflow valve
14. Electrically, cabin pressure controller
15, Over pressurization
True or False
1. true
2. false; they are painted green.
3. true
4. false; indicates that the pressure relief valve has opened and this should be investigated.
5. true
6. true
7. false; below 8,000
8. true
9. false; turbochargers are the most common.
10. false; turbochargers are driven by exhaust gases.
Knowledge Application
1. outflow valve
2. Bleed air from the turbine‐engine compressor
3. The cabin pressure controller.
4. Gasoline combustion heater, electric heater, and exhaust shroud heat exchanger.
5. carry the heat where it is needed
6. expansion turbine, air‐to‐air heat exchangers, water separator, and various temperature control valves.
7. The compressed air turns a turbine, and it undergoes a pressure and temperature drop.
8. moist air passes through a fiberglass bag that condenses the moisture in droplets, vanes swirl the air and droplets are collected and drained.
9. The compressor pressurizes low pressure vapor into high pressure vapor. The condenser cools the high pressure vapor with outside air and turns it into a high pressure liquid. At the expansion valve the high pressure liquid changes into a low pressure liquid. In evaporator the low pressure liquid absorb s cabin heat and change into a low pressure vapor and returns to the receiver dryer where the process is repeated again.
10. When the pack valve opens hot high pressure bleed air flows to air mix valve. Depending on temperature a certain amount of this bleed air travels to the mixing chamber and the rest flows to the primary heat exchanger to be cooled. The bleed air will travel through a second mixing valve and enters the compressor of the air cycle machine. The pressure and temperature of the bleed air increases. The bleed air will flow through the secondary heat exchanger where its temperature is lowered by ambient air. After the secondary heat exchanger the air enters the aircycle machine. Here the air temperature lowers because energy in the air drives the turbine which in turn drives the compressor. The shape of the turbine blades expand the air which lowers in pressure and temperature. The air that leaves the air cycle machine flows through the water separator where moisture is removed. When the sensor at the water separator senses 35 degrees the anti‐ice control valve opens to allow warmer air to mix with the air leaving the air cycle machine. The air that leaves the water separator will flow to the mixing chamber where it is mixed with hot bleed air. Temperature control is realized by positioning the two mixing valves so that the desired temperature is achieved.
Multiple Choice
1. c
With gas turbine engines, the cabin can be pressurized by bleeding air from the engine compressor. Usually the air bled from an engine compressor is sufficiently free from contamination and can be used safely for cabin pressurization.
2. a
An air cycle cooling system consists of an expansion turbine (cooling turbine) , an air-to-air heat exchanger, and various valves which control airflow through the system. High pressure air from the cabin compressor is routed through the turbine section. As the air passes through the turbine, it rotates the turbine and the impeller. When the compressed air performs the work of turning the turbine, it undergoes a pressure and temperature drop.
3. c
When the Freon® gas leaves the compressor in a vapor cycle air conditioning system, it flows to the condenser. At the condenser, the gas passes through a heat exchanger where outside (ambient) air removes heat from the Freon®. When the heat is removed from the Freon® gas, the gas changes to a liquid and a great amount of heat is given up.
4. b
Regardless of size, every combustion heater needs four things for operation: (1) Fuel to burn; (2) Ignition to ignite the fuel; (3) Combustion air to provide the oxygen required to support the flame; and (4) Ventilating air to carry the heat to the places where it is needed.
5. c
When gas turbine engines are involved in the cabin pressurization process, the air is usually bled from the engine's compressor. This air is generally referred to as bleed air.
6. b
To prevent too much air from entering the heaters as air pressure increases, either a combustion air relief valve or a differential pressure regulator is provided.
7. b
Cabin pressurization is obtained by flowing more air than is needed into the cabin, and controlling the exhaust of excess air.
8. a
What the cabin pressure regulator does, and how it controls the outflow valve, is determined by cabin air pressure.
9. b
An air cycle cooling system consists of an expansion turbine (cooling turbine) , an air-to-air heat exchanger, various valves to control airflow, and a source of high pressure air.
10. c
A dump valve in a pressurization system might be operated by a switch in the cockpit. The purpose of the dump valve is to release the cabin air pressure to atmosphere.
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