Answers - Cabin Environmental Control

Fill in the Blanks

1. 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
16. Negative relief valves
17. Vapor cycle, air cycle
18. Engine compressor, APU
19. Refrigeration turbine unit, air cycle machine
20. Thermistors, resistance
21. Liquid, vapor
22. Receiver dryer
23. Copper, aluminum
24. Exhaust gases
25. Cleaning filters, spark plug


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.
11. true
12. false; differential control mode of a cabin pressurization system controls pressure to maintain a constant pressure between the air outside the cabin and the ambient air.
13. true
14. false; prevent cabin over pressurization.
15. true
16. true
17. false; a swirling motion will separate the water droplets.
18. true
19. false; It is an closed system
20. false; R134‐A has replaced R12
21. true
22. false. should feel cool.
23. true
24. false; use a exhaust shroud heating system.
25. false; drawn from an aircraft fuel tank.

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.

11. A receiver dryer, evaporator, compressor, condenser, and expansion valve.
12. oxygen flows from a charged cylinder through a high pressure line to a reducing valve and to mask outlets.
13. system must be purged to remove moisture
14. dry nitrogen, dry air, or oxygen
15. aviators' breathing oxygen
16. provide lubrication and prevent compressor failure
17. use oil free tools, clothing, hands, adequate eye protection
18. turbocharger, supercharger, engine driven compressor
19. small amount of LOX can be converted to an enormous amount of gaseous oxygen, thus needing little storage space.
20. cabin altitude, rate of change, and barometric correction and pressurization mode

Multiple Choices

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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