Environmental Systems

Question 1

What are the two main gasses that make up our atmosphere?

Answer 1

Nitrogen and oxygen.

Question 2

Why are the cabins of most turbine-powered aircraft pressurized?

Answer 2

These aircraft fly at such high altitudes that supplemental oxygen would be needed for the occupants if the cabins were not pressurized.

Question 3

Where does the pressurizing air come from on most turbine-powered aircraft?

Answer 3

From air bled from one of the engine compressors.

Question 4

Where does the pressurizing air come from on most of the smaller reciprocating-engine-powered aircraft?

Answer 4

From the engine turbocharger.

Question 5

What determines the amount of pressurization that an aircraft can use?

Answer 5

The structural strength of the aircraft cabin.

Question 6

How is cabin pressure controlled in a pressurized aircraft?

Answer 6

More pressure than is needed is pumped into the aircraft cabin, and the pressure controller modulates the outflow valve to maintain the correct pressure in the cabin.

Question 7

What is meant by the isobaric mode of cabin pressurization?

Answer 7

The isobaric mode of cabin pressurization is the mode that keeps the cabin altitude constant as the aircraft changes its flight altitude.

Question 8

What is meant by the constant differential mode of cabin pressurization?

Answer 8

After the pressure in the aircraft cabin reaches the maximum value that is allowed by structural considerations, the constant differential mode of operation is the mode that holds the pressure inside the cabin a constant amount above the outside air pressure.

Question 9

What is the function of the cabin outflow valve on a pressurized aircraft?

Answer 9

The cabin outflow valve, which is controlled by the pressure controller, maintains the correct amount of pressure inside the cabin.

Question 10

What is the function of the cabin pressure safety valve on a pressurized aircraft?

Answer 10

It prevents cabin pressure from exceeding the maximum allowable differential pressure.

Question 11

Why must pressurized aircraft have a negative pressure relief valve?

Answer 11

The structure of an aircraft cabin is not designed to tolerate the inside pressure being lower than the outside pressure.

Question 12

What keeps the cabin of a pressurized aircraft from being pressurized when the aircraft is on the ground?

Answer 12

A squat switch on the landing gear holds the safety valve open when the aircraft is on the ground.

Question 13

What are two types of air conditioning systems that may be installed on an aircraft?

Answer 13

Air cycle systems and vapor cycle systems.

Question 14

Where does the warm air come from that is used to heat the cabin of a large jet transport aircraft?

Answer 14

Warm engine compressor bleed air is used.

Question 15

Where does the warm air come from that is used to heat the cabin of most small single engine reciprocating-engine-powered aircraft?

Answer 15

From a shroud around the engine muffler.

Question 16

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

Answer 16

From the aircraft fuel tanks.

Question 17

What happens to a combustion heater if the flow of ventilating air is restricted?

Answer 17

If the ventilating air is restricted and the temperature reaches a preset value, the limit switch will cause the fuel to be shut off to the heater.

Question 18

How is the heat removed from an aircraft cabin with a vapor-cycle air conditioning system?

Answer 18

The cabin heat is absorbed by the refrigerant in the evaporator, and it is carried outside the aircraft where it is given up to the outside air in the condenser.

Question 19

What produces the cool air in a vapor-cycle air conditioning system?

Answer 19

Warm cabin air is blown across the evaporator where its heat is transferred into the refrigerant. The air that leaves the evaporator is cool.

Question 20

Why must air cycle air conditioning systems incorporate a water separator?

Answer 20

The rapid cooling of the air in the expansion turbine causes moisture to condense in the form of fog. This moisture is trapped in the moisture separator before the air is released into the cabin.

Question 21

What is used as the refrigerant in a vapor-cycle air conditioning system?

Answer 21

A Freon liquid refrigerant known as Refrigerant 12, or the more environmentally friendly R-134a.

Question 22

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

Answer 22

As a high-pressure gas, in its liquid form, and as a solid in the form of a chemical candle.

Question 23

What kind of gaseous oxygen must be used to service an aircraft oxygen system?

Answer 23

Only aviators’ breathing oxygen. Hospital oxygen and welding oxygen contain too much moisture to be used.

Question 24

What is used to check an oxygen system for leaks?

Answer 24

A special leak detector liquid that is a form of non-oily soap.

Question 25

What is a continuous-flow oxygen system?

Answer 25

An oxygen system that continuously flows a metered amount of oxygen into the mask.

Question 26

What is a pressure-demand oxygen system?

Answer 26

An oxygen system that flows oxygen to the mask only when the wearer of the mask inhales. Above a specified altitude, the regulator meters oxygen under pressure into the mask when the wearer inhales.

Question 27

What identification must be stamped on an oxygen bottle that is carried in an aircraft?

Answer 27

The identification DOT 3AA or DOT 3HT, the date of manufacture, and the date of all of the hydrostatic tests.