Pressurization & High altitude operations

Question 1

What are the advantages of flying higher?

Answer 1

-Less traffic
-Avoid terrain and weather
-Higher TAS

Question 2

What are the disadvantages of flying higher?

Answer 2

-Air is thinner, so engines need to be specialized to work well
-Colder, risk of freezing
-No oxygen, risk of hypoxia

Question 3

What does Dybarism mean?

Answer 3

Refers to a physiological disorder brought about by changes in pressure

Question 4

What are the 3 major ways to prevent hypoxia from starting?

Answer 4

-Supplemental oxygen
-Pressurize cabin
-Pressurize oxygen

In passenger aircraft, we usually add oxygen or pressurize the environment

Question 5

Typically, how much oxygen is in a portable oxygen tank?

Answer 5

Enough to support 4 people at 18,000 ft for 90 minutes (generally)

Question 6

What is solid-state oxygen?

Answer 6

Solid chemicals that interact with each other to form oxygen

Question 7

What type of regulators and oxygen masks are there?

Answer 7

-Continuous flow
-Demand system
-Pressure Demand

Question 8

What is a continuous flow regulator/mask?

Answer 8

They provide a flow of 100% oxygen, measured in litres per minute. The amount of oxygen released must be metered out based on altitude

Question 9

What is the difference between a manual and an automatic continuous flow system?

Answer 9

A manual system requires the pilot to adjust the flow rate as they flow, while an automatic system adjusts the flow rate using an aneroid barometer

Question 10

Why do continuous flow masks not have an airtight seal?

Answer 10

So there’s room for expelled air from the lungs to escape. And, we have a rebreather bag to trap the air we breathe out to be reused

Question 11

How much of what we breathe OUT is oxygen?

Answer 11

16.4%

Question 12

How high up can you use a continuous flow mask?

Answer 12

Somewhere between FL180 and FL250 is your limit

Question 13

Why do continuous flow masks not work very well after FL250?

Answer 13

Because there isn’t enough pressure to get the air into your lungs

Question 14

What mask style does a demand air system use?

Answer 14

An air-tight face mask with a sensor that senses when the user inhales, prompting it to supply air

Question 15

How much oxygen do demand air systems provide?

Answer 15

Up to 100% oxygen. It is mixed with ambient air controlled by a lever called an automizer lever(which is sometimes replaced with an aneroid barometer)

Question 16

How high up does a demand air system work?

Answer 16

Up to FL350

Question 17

What is the difference between a demand system and a pressure demand system?

Answer 17

The difference is that a pressure demand system will pressurize the oxygen into your lungs. Ensuring the oxygen has a higher pressure than the air inside your lungs, allowing it to travel across your membrane

Question 18

How should you check oxygen systems during pre-flight?

Answer 18

-Fit
-Ensure the tanks are full
-Oily hands, chapstick, lipstick, skin cream, etc, will mess with your system
-Ensure no leaks
-Make sure it’s the right type of oxygen
-Ensure no sources of combustion
-No overfilled tanks
-No expired tanks

Question 19

Why do we pressurize cabins?

Answer 19

For comfort and crew effectiveness

Question 20

What are the advantages of a pressurized cabin?

Answer 20

-Don’t need to carry supplemental oxygen
-Cabin environment can be more easily controlled
-Ease of movement within the cabin
-Ease of communication

Question 21

What do we need to pressurize a cabin?

Answer 21

-A structure strong enough to withstand the outward forces that the pressure will create
-A source of compressed air
-A temperature regulator for incoming air
-An outflow air regulator

Question 22

What do small piston aircraft use to pressurize the cabin?

Answer 22

They use turbo air

Question 23

What does the flow control unit do?

Answer 23

It diverts some of the air from the compressors to the cabin before it is mixed with the fuel, but it prioritizes the engine over the cabin

Question 24

What do large turbine jets use to pressurize the cabin?

Answer 24

They use bleed air from the compressor section of the turbine

Question 25

What does the bleed air have to do before entering the cabin?

Answer 25

It needs to cool off. Usually, by mixing with the surrounding air(external air mizer, used by bigger planes), or we run the tube over outside air(intercooler, used by smaller planes)

Question 26

How much air do we flow into the cabin?

Answer 26

The maximum amount we can get in, then we select how much air can escape to control the cabin altitude

Question 27

What usually determines the altitude operating limit of a large aircraft?

Answer 27

The maximum cabin differential. The pressure difference between outside air and air inside the cabin increases with height. Eventually, this difference creates too much force on the airframe. Thus, we get our operating limit

Question 28

What are dump valves, and when do we use them?

Answer 28

They open up to depressurize the airplane in case it is pressurized when it shouldn't be. Like when we taxi, we do not want a pressurized cabin

Question 29

What are safety valves, and when do we use them?

Answer 29

They depressurize the aircraft when the pressure gets dangerously high

Question 30

Why are aircrafts not pressurized during taxi?

Answer 30

Because the squach switch is almost always connected to the dump valve, while the wheels are on the ground, we can not close it and pressurize the cabin