Auxiliary

• Oxygen is essential for cabin function 

• At high altitudes, the air is thin, making it harder to breathe

• Aircraft systems simulate lower altitudes inside the cabin  

Importance of oxygen system to sustain life

• can occur due to structural failure or system malfunction 

• Rapid decompression can cause immediate  

• Symptoms include dizziness, confusion, and unconsciousness. 

Cabin Decompression and Hypoxia

• is taken from the engine to pressurize the cabin 

Aircraft Bleed Air System 

• system is more advanced than passenger systems

• Includes full-face mask with communication devices

• Ensures crew manage the aircraft during emergencies 

Crew oxygen system 

Types of aircraft oxygen systems:

• Portable Gaseous Oxygen System

• On-Board Oxygen Generating System 

• Liquid Oxygen System 

• Pure Gaseous Oxygen

• Gaseous Oxygen Systems

• Oxygen Storage Cylinder

• Oxygen Systems and Regulators 

Use Compressed oxygen stored in cylinders

Gaseous Oxygen Systems

Integrated Into the aircraft, ready for use in emergencies

Built in Oxygen Systems

Provides 100% oxygen for the crew.

Pure Gaseous Oxygen

Stores the oxygen used in both crew and passenger systems  

Oxygen storage cylinders

Controls the flow and pressure of oxygen to ensure safety and effectiveness 

Oxygen Systems and Regulators:

Ensures enough oxygen is available for passengers and crew to prevent symptoms like confusion, loss of consciousness and severe cases.

Hypoxia Prevention

High altitudes reduce drag, making flights faster and more fuel-efficient.

Efficient Flight at High Altitudes

Pressurization mitigates risks of decompression and rapid changes in altitude

Safety Considerations

Air is drawn from the engines (bleed air) or Auxiliary Power Unit (APU)

Air Intake

These Valves control the amount of air entering and leaving the cabin

Pressurization Valves

Pack systems control air temperature by mixing hot and cold air

Temperature Regulation

Controls air release to maintain pressure balance

Outflow Valve

The Cabin Pressure is controlled by air conditioning packs. 

Temperature Regulation and Comfort

Used for heating the cabin

Hot Bleed Air

Mixed to cool the cabin

Cold Ram Air

Bleed air from the engines or auxiliary power unit (APU)

Air Source

ACA or VCC systems for temperature control.

Cooling Units

Used in both ACA and VCC systems

Heat Exchangers

Distributes conditioned air to the cabin

Cabin Outlets

• uses bleed air from the engine

• Core components: Compressors, turbine, and heat exchangers

• Ideal for high-performance, large aircraft

Air cycle air cycling (ACA)

Basic Components of Aircraft Air Conditioning:

• Zone And Pack Controllers

• Ram Air

• Mixing and Distribution 

• Engine Bleed

• Pack (Pneumatic Air Conditioning Kit)

• APU Bleed (Auxiliary Power Unit)

• Regulate temperature in different sections of the cabin

• to ensure proper air conditioning is maintained. 

Zone and Pack Controllers

• Provides cooling for the heat exchangers in PACKS

• Draws outside air through air scoops, especially during flight, when the aircraft is moving at high speed.

Ram Air:

• High pressure, high temperature air taken from the aircraft engines

• Used for air conditioning, pressurization and anti-icing

Engine Bleed

• Core of the air conditioning system

• Cools, filters, and adjusts the air pressure.

PACK (Pneumatic Air Conditioning Kit):

• provides bleed air when the engines are off

• Used for cabin air conditioning and starting the engines

APU Bleed (AUXILIARY POWER UNIT)

• Combines fresh, cooled bleed air with recirculated cabin air.

• Distributes air evenly throughout the cabin via ducts and diffusers 

Mixing and Distribution

• similar to refrigeration systems.

• Ideal for smaller aircraft 

• Components: Compressed, Evaporator, Condenser

Vapor Cycle Cooling (VCC)

R12(Dichlorodifluoromethane)

R134a - A safer refrigerant with a boiling point of -15

Refrigerant

Acts as a reservoir for excess refrigerant 

Receiver Dryer

Regulates the flow of the refrigerant into the evaporator, ensures optimal cooling by controlling the refrigerant state change 

Expansion Valve

• Heat Absorption: High-Pressure, High temperature 

• Cooling: Refrigerant changes to low pressure vapor

• Airflow: Cabin air is blown over the evaporator 

Evaporator

• Circulates Refrigerant: Receives low pressure vapor and compresses it 

• Pressure increase: Raises the temperature and pressure of the refrigerant 

Compressor

• Heat Exchange: Removes heat from high-pressure, high-temperature refrigerant.

• State change: Converts refrigerant from vapor to liquid

Condenser

• Access Points: For servicing and maintenance 

• Types: high-side and low-side

Service Valves

Used in larger aircraft, relies on engine bleed air, efficient at high altitudes

Used in smaller aircraft, operates independently of bleed air, refrigerant-based

ACA and VCC

• The pressurization system controls the cabin environment at high altitudes by regulating air pressure

• Key Components: Outflow valve, pressure sensors, safety relief valve

Aircraft Pressurization System

• Ensures proper functioning and check for wear

Inspect Outflow Valves

• Test the sensors for accurate pressure readings

Check Pressure Sensors

Ensures it opens at the correct pressure to prevent over pressurization

Test Safety Relief Valve

• Check for leaks and replace damage components      

Inspection Ductwork and Seals

• The backup system is used when the primary pressurization fails

Alternate Air Source

• Check for blockages or damage

Inspect Alternate Inlets

• Ensure proper functioning under load

Test Backup Pressure Controls:

• Verify seamless switching between primary and alternate air sources.

Check the switching mechanism