Chapter 3 - Aircraft Environmental and Oxygen Systems

Question 1

What are some potential causes of hypoxia in aviation?

Answer 1

Ascent to altitude

Failure of equipment to supply at adequate concentration or pressure

Decompression of cabin at altitude

Presence of toxic fumes

Question 2

What causes hyperventilation?

Answer 2

Partial pressure of CO2 in the blood is too low ventilation of lungs exceeds rate of production.

Caused by:
Anxiety, apprehension or fear
Rise in body temp
Whole body vibration at 4-8Hz
Hypoxia

Question 3

What are some symptoms of hyperventilation?

Answer 3

Tingling in hands, feet and lips

Vague feeling of unreality

Light-headedness/dizziness

Faintness

Spasms of muscles in hands/feet

Impaired performance

Unconciousness

Question 4

What causes barotrauma and what are the symptoms?

Answer 4

Imbalance of pressure on the eardrum when the contraction and expansion of gas in the middle ear cavities and sinuses fail to balance pressure through the nose.

Symptoms:
Pain in ears, teeth and/or sinuses
Deafness
Ruptured eardrum

Question 5

What altitude are civilian/transport aircraft pressurised to?

Answer 5

6000-8000ft (8000ft most likely answer in exam)

Question 6

What altitude are combat aircraft pressurised to?

Answer 6

25,000ft

Question 7

What is ‘Cabin Differential Pressure’?

Answer 7

The pressure difference acting on the structure of the aircraft.

Max is based on the fuselage design strength and limits the aircraft’s operational ceiling.

Question 8

Where is the air to pressurise the cockpit/cabin usually obtained from?

Answer 8

A late compressor stage

The high pressure and high temp air is regulated and conditioned before being fed into the cabin.

Question 9

What controls cabin pressure and its rate of change?

Answer 9

The control module

Achieved by regulating the release of air to the atmosphere through a discharge valve(s) in the aircraft skin.

NOTE - Learn diagrams from the course manual + be able to label

Question 10

What two safety devices are incorporated into an aircraft pressurisation system?

Answer 10

Safety relief valve

Inward relief valve

Question 11

When does a safety release valve operate/what is its purpose?

Answer 11

If cabin differential pressure approaches the max permitted, it is sensed by the safety relief valve, which is INDEPENDENT of the normal control system.

Valve automatically opens to dump air OUTWARDS, reducing the interior cabin pressure.

Question 12

When does an inward release valve operate/what is its purpose?

Answer 12

If outside air pressure becomes too much greater than cabin pressure (e.g. in a very rapid descent), allows air in to balance the pressure differential.

Question 13

What is the role of the aircraft ventilation system?

Answer 13

Maintain a flow of air around/through the cabin/cockpit to keep the temperature and humidity comfortable + prevent the build up of carbon dioxide, water vapour, dust, fumes and odours.

Passenger a/c airflow = approx. 1.5kg/min
Combat aircraft airflow = approx. 5kg/min

Question 14

What is the ‘Comfort Zone’?

Answer 14

The range of ambient temperatures and humidity in which a crew can operate comfortably without rapidly becoming fatigued.

Question 15

How is air from the late compressor stage cooled before being used for cabin pressurisation and ventilation?

Answer 15

Routed through primary and secondary heat exchangers and a cold air unit, as necessary.

Finally, passes through a mixture chamber, where it is combined with hot moist-by-pass air and recycled cabin air.

Heat exchangers - Cooled by indirect contact with cool ram air

Cold air unit - Cooled by the principles of expansion and energy conversion (temp must reduce)

NOTE - LEARN + be able to label the diagram in course manual

Question 16

What else is pressurised and conditioned air used for on aircraft?

Answer 16

Pressurise + cool avionics modules

Seal canopies

Supply pressure for aircrew anti-g clothing

Question 17

What is required of the O2 supplied by an onboard oxygen system?

Answer 17

High standard:

99.5% O2
Lower water and carbon monoxide content

Question 18

What is MSOCs?

Answer 18

Molecular Sieve Oxygen Concentrators

Used for on-board oxygen generation (OBOGS)

Question 19

What are the three types of O2 system commonly used?

Answer 19

Gaseous O2 system

Liquid O2 system

Molecular Sieve O2 Concentrator (MSOC)

Question 20

What are the advantages and disadvantages of using a gaseous O2 system?

Answer 20

Oxygen held in cylinders

Advantages:

• Simple
• Oxygen not lost by venting when not in use and can be used immediately after filling

Disadvantages:

• Cylinders are bulky and heavy, unsuitable for primary O2 supply
• Could be explosive if tanks were punctured

Question 21

What are the advantages and disadvantages of using a liquid O2 system?

Answer 21

Advantages:

• LOX has an expansion rate almost 7 times greater than gaseous O2, so can hold a lot more in a smaller tank
• Takes up less weight and space

Disadvantages:

• Evaporation and venting losses, means it needs to be recharged at frequent intervals
• LOX takes a long time to stabilise once in the converter and may be upset if the container is agitated, e.g. aerobatics
• LOX prone to contamination by toxic materials

Question 22

What are the advantages and disadvantages of using an MSOC O2 system?

Answer 22

Advantages:
- Efficient removal of contaminants

Disadvantages:

• Separate gas supply still required for crew ejection
• Not all MSOCs are able to provide enough O2 to prevent hypoxia following rapid cabin decompression

Question 23

How does a MSOC work?

Answer 23

Synthetically produced porous metal.

Removes nitrogen from air passed through it under pressure.

Question 24

What is pressure swing absorption?

Answer 24

When an MSOC is saturated with nitrogen, the nitrogen is removed by depressurising the bed to ambient pressure, followed by back-purging with a portion of the product gas.

Question 25

What are the two principle forms of EO (Emergency Oxygen) assembly?

Answer 25

Continuous flow

On demand

Question 26

What is ‘continuous flow’ EO?

Answer 26

Fitted to ejection seats.

O2 stored as a gas in a cylinder mounted to the seat.

Approx. 10 mins of oxygen

Question 27

What is ‘on demand’ EO?

Answer 27

Fitted to ejection seats + parachute packs.

Stored as a gas in cylinders.

O2 through a regulator to the user, which controls the flow. Duration depends upon the rate the user uses it up.