Cabin Atmosphere Control systems

Question 1

What is the principle control element in a cabin pressurization system?

Answer 1

The cabin outflow valve.

Question 2

What is the purpose of the negative pressure relief valve in the pressurization system?

Answer 2

The negative pressure relief valve prevents accidentally obtaining a cabin altitude which is higher than the attitude of the aircraft.

Question 3

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

Answer 3

The cabin pressure controller, located in the cockpit is used to set the cabin air pressure to a desired
altitude, normally between six and eight thousand feet.

Question 4

What are the two groups of independent cabin compressors?

Answer 4

They are positive displacement, and centrifugal compressors.

Question 5

What method is used by turbine powered aircraft for pressurization?

Answer 5

Bleed air from the turbine engine compressor.

Question 6

What limits the degree of cabin pressurization?

Answer 6

The structural design features of the fuselage, and by the capacity of the superchargers to maintain
a constant volume of airflow to the fuselage.

Question 7

Where does the warm air for cabin heating come from in most small reciprocating engine aircraft?

Answer 7

From the shroud around the engine muffler.

Question 8

What are three methods of supplying heat to the conditioned air when the heat of compression” is not sufficient for this purpose?

Answer 8

Fuel burning combustion heaters, electric heaters, and exhaust gas air-to-air heat exchangers.

Question 9

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

Answer 9

It is the air that is warmed and sent into the cabin.

Question 10

Where does the fuel used in an aircraft combustion heater come from?

Answer 10

The aircraft fuel tanks.

Question 11

What controls the temperature in an aircraft cabin that is heated with a combustion heater?

Answer 11

A thermostat.

Question 12

What are the sources for ventilation air in a combustion heater?

Answer 12

A blower/fan or ram-air.

Question 13

What are the components of an air cycle cooling system?

Answer 13

An expansion turbine (cooling system), an air-to-air heat exchanger, and various valves.

Question 14

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

Answer 14

The compressed air performs the work of turning the turbine and it undergoes a pressure and temperature drop.

Question 15

What are the components in a vapor cycle (Freon) cooling system?

Answer 15

The compressor, condenser, a receiver dryer, expansion valve, and evaporator.

Question 16

How do you determine the liquid level in a vapor cycle cooling system?

Answer 16

Operate the system for about 5 minutes to reach a stabilized condition, and then watch the flow of
Freon through the sight glass. A steady flow indicates enough charge. If the Freon is low,
bubbles will appear in the sight glass.

Question 17

what is the vapor-cycle cooling?

Answer 17

Specialized refrigerant oil. (a closed system in which a refrigerant is circulated through tubing and a variety of components to remove heat from the aircraft).

Question 18

how does a continuous flow oxygen system operate?

Answer 18

Oxygen flows from a high-pressure cylinder through a high pressure line to a reducing valve and to mask outlets.

Question 19

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

Answer 19

The system must be purged to remove moisture.

Question 20

What safety considerations must be observed when filling oxygen cylinders?

Answer 20

Oxygen cylinders should be filled in an oil free environment. The mechanic who fills the cylinders
should not have any petroleum products on their clothes, hands, or in their hair.

Question 21

What is the main chemical agent inside of an oxygen generator?

Answer 21

Sodium chlorate is the main chemical agent used in aviation oxygen generators. The chemical is
ignited by a spark-emitting cap, and when it burns, O2 is generated. These systems are lighter and
less complex than oxygen storage based systems. The main drawback of oxygen generators is that
once the burning of the sodium chlorate begins, it cannot be stopped until the chemical is consumed.

Question 22

How are high and low pressure oxygen cylinders identified?

Answer 22

High pressure (1800-1850 psi) oxygen cylinders are green in color and have the words “Aviator’s
Breathing Oxygen” stenciled lengthwise in white, one inch letters. Low pressure (400-425 psi)
cylinders are painted light yellow.

Question 23

What are the three ways supplemental oxygen can be carried in an aircraft?

Answer 23

As liquid oxygen, a high pressure gas, or a chemical candle.

Question 24

What is an acceptable lubricant for installing oxygen system fittings?

Answer 24

Teflon, or water based lubricants.

Question 25

Why is oil added to a vapor-cycle freon system?

Answer 25

To seal and lubricate the compressor.

Question 26

What is a roots blower?

Answer 26

An engine-driven compressor.

Question 27

How does water separator remove moisture from the air?

Answer 27

The moist air passes through vanes that swirl the air, and the droplets are collected and drained.

Question 28

What safety precautions should be observed when servicing oxygen system?

Answer 28

Clean, grease free tools, clothing, hands, no smoking or open flames within 50 feet, do not use adhesive tape of any kind.

Question 29

What is used to purge oxygen lines of moisture?

Answer 29

Dry nitrogen, dry air, or oxygen.

Question 30

What type of oxygen must be used in aircraft?

Answer 30

Aviators breathing oxygen.