Reference Books

• Pilot's Handbook of Aeronautical Knowledge(FAA-H-8083-25B). (2016). Oklahoma City, OK: United States Department of Transportation, Federal Aviation Administration, Airman Testing Standards Branch.
• Commercial/Instrument Flying Handbook faa-h-8083-15B. (2012). Oklahoma City, OK: United States Department of Transportation, Federal Aviation Administration, Airman Testing Standards Branch.
• Commercial Pilot Syllabus (10001785-003). (2015). Englewood, CO: Jeppesen

Reference Multimedia

• Kakesako, G. K. (2017, February 1). Hero pilot of United Flight 811 dies at age 81. Retrieved from https://www.staradvertiser.com/2010/10/06/breaking-news/hero-pilot-of-united-flight-811-dies-at-age-81/.
• (2017). ATPL Training / Airframes & Systems #41 Pneumatics - Pressurization Retrieved from https://www.youtube.com/watch?v=i9vnn_ZhNbA.

Oxygen systems

Types of oxygen systems

Portable Oxygen System

Fixed Oxygen System

Each system is divided into three different components

(Carry Oxygen)

1) Oxygen Storage

2) Oxygen Regulator

3) Mask or Nasal Cannulas

(Regulates Oxygen)

(Delivers Oxygen)

Oxygen components on the Flight deck

Oxygen Regulator

• A regulator provides different amounts of oxygen flow to match increasing need as altitude increases.

• These regulators can be manual or automatic in design. Consist of three different categories.

Continuous-Flow

Diluter-Demand

Pressure-Demand

Pressure Mask

• Pressure demand masks force oxygen into the lungs as you breathe. 

• High pressure combined with 100% oxygen keeps the oxygen's partial pressure high enough for the lungs to absorb a safe level of O2.

Inspection of Masks and Hoses

Pressure

Regulator

Indicator

Connections

Emergency

Check for enough oxygen pressure and quantity to complete the flight

Make sure the outlet assembly and plug-in coupling are compatible. 

Flow indicators may be located on the regulator or within the oxygen delivery tube. Check for green colored.

Ready to use for those emergencies that call for oxygen. Brief passengers on location and proper use.

Ensure that all connections are secured.

Follow the PRICE Check:  

Continuous-Flow

Continuous-Flow

• A continuous-flow allows continuous delivery of oxygen to the user even when exhaling.

• Relatively low cost and simplicity, they are installed on reciprocating-engine airplanes, but they are also installed for passenger use in some turboprops and jets.

Mask/Nasal Cannulas

Cannula

Phase Sequential Mask

Diluter-Demand Mask

• Continuous-flow oxygen masks are simple devices made to direct flow to the nose and mouth of the wearer. 

• There are three different types of Mask or Nasal Cannulas. 

Rebreather Mask

Cannula

• The cannula is the most simple oxygen mask. It fits around the nose.

• The cannula pumps a constant stream of oxygen in as the person breaths as usual. FARs limit their use to 18.000 feet.

Rebreather Mask

• A bag inflates to store exhale Air to mix with 100% Oxygen.

• This conserves oxygen by permitting lower flow rates in continuous flow systems. It can be used up to 25.000 feet. 

Phase Sequential Mask

• Phase sequential mask allows the user to go to higher altitudes up to 40,000 feet.

• This mask uses a series of one-way ports that allow a mixture of 100% oxygen and cabin air into the mask.

• Exhalation is vented to the atmosphere; as a result, the bag does not inflate.

Diluter-Demand

• The type of mask used is a quick- donning mask design, the mask can be put on rapidly and seals around the face. 

• The mask only supplies oxygen as the pilot breathes. It automatically mixes oxygen and air only as you inhale, a diluter demand will last longer than a continuous flow.

• Diluter demand masks can be used up to 40.000 feet. 

Connecting and Using Oxygen Equipment

Before a high-altitude flight, instruct passengers on how to connect and use oxygen masks or cannulas. Let them take a few sample breaths to ensure they are comfortable with the system. Smoking is strictly prohibited when oxygen is in use, as it can accelerate combustion and create a serious fire hazard. Proper preparation on the ground prevents distractions and enhances safety in flight.

Diluter-Demand

Diluter-Demand

The diluter-demand type regulator holds back the flow of oxygen until the user inhales.

During the hold and exhalation periods of breathing, the oxygen supply is stopped.

With its control toggle switch set to normal, the amount of dilution depends on the cabin altitude. At approximately FL340 feet, the diluter-demand regulator meters 100 percent oxygen.   

A demand valve connected to the diaphragm opens, letting oxygen flow through the metering valve.

The metering valve adjusts the mixture of cabin air and pure oxygen via a connecting link to an aneroid that responds to cabin altitude.

Pressure-Demand

Pressure-Demand

Pressure-demand oxygen systems operate similarly to diluter demand systems, except that oxygen is delivered through under higher pressure.

Forcing oxygen into the lungs under pressure ensures saturation of the blood

Pressure-demand regulators are used on aircraft that regularly fly at 40,000 feet and above.

Pulse-Demand

Pulse-Demand

Efficient Oxygen Delivery: Pulse-demand systems provide oxygen only when inhaling, reducing oxygen use by up to 85% compared to continuous-flow systems.

Adaptive Oxygen Supply: A barometric sensor adjusts oxygen delivery based on cabin altitude, ensuring proper dosage at higher altitudes.

Safety Considerations: Misuse or improper integration with built-in systems can lead to fatal accidents; always follow manufacturer instructions strictly.

Oxygen Storage

Oxygen Storage

Gaseous-state

Liquid-state

Solid-state

Stored and transported in high-pressure cylinders. Rated for 1800–1850 psi of pressure and capable of maintaining pressure up to 2,400 psi.

LOX systems are used in the military. This storage uses pipes to convert the liquid into usable gas.

Supplementary oxygen system used as a backup on pressurized aircraft in case of pressurization failure. The system uses solid chemical oxygen generators that are most common on airliners. Require less space and weigh less than gaseous oxygen systems

Oxygen Servicing

Oxygen cylinder is charged to a pressure of 1,800 to 1,850 p.s.i. Maximum pressure of approximately 2,200 p.s.i.

A pressure relief valve prevents exceeding the maximum pressure. Makes sure the oxygen system is filled with a 99% aviator’s breathing oxygen.

The Airport/Facility Directory contains information on airports that can provide oxygen system servicing.

Cabin Pressurization

A cabin pressurization system ensures adequate passenger comfort and safety.

It must be capable of maintaining a cabin pressure altitude of approximately 8,000 feet or lower regardless of the cruising altitude of the aircraft.

Ensure that passengers and crew have enough oxygen present at sufficient pressure to facilitate full blood saturation.

Decompression sickness and sinus or ear blockages are among some of the physiological conditions that can cause severe pain or discomfort to you or your passengers.

Pressurization Principles

Air is pumped into the cabin at a constant rate sufficient to raise the pressure slightly above that which is needed.

Control is maintained by adjusting the rate at which the air is allowed to flow out of the aircraft.

Aircraft altitude

Ambient temperature

Ambient pressure

Cabin Pressure Altitude

Cabin Differential Pressure

The following terms will aid in understanding the operating
principles of pressurization and air conditioning systems:

1. Aircraft altitude: The actual height above sea level at
which the aircraft is flying.​

2. Ambient temperature: The temperature in the area immediately surrounding the aircraft.

3. Ambient pressure: The pressure in the area immediately surrounding the aircraft.

4. Cabin Pressure altitude: Cabin pressure in terms of the equivalent altitude above sea level.

5. Differential pressure: The difference in pressure between the pressure acting on one side of a wall and the pressure acting on the other side of the Wall. In aircraft air-conditioning and pressurizing systems, it is the difference between cabin pressure and atmospheric pressure.

Cabin Pressure Differential is 6.1 psi.

Pressurization Components

The components of the cabin pressure system are: 

Compressor 

Outflow valves (Cabin pressure regulator)

A Safety valve

Flight deck controls

1. Ambient Air is Introduced into a compressor.

2. A heat exchanger cools the air.

3. Then the cool air is sent to the cabin (via outlets).

4. Cabin pressure is then regulated with the Outflow Valves.

5. Safety/Dump valve prevents cabin pressure from exceeding a predetermined differential pressure above ambient pressure.  

The flight deck control is the device used to control the
cabin air pressure. It also actuates the dump valve.

The Cabin/Differential pressure indicator indicates the difference between inside and outside pressure.

Indicates the pressure cabin rate of climb or descent. 

Opening the valve, increases the outflow, reducing the cabin pressure and causing the cabin to climb.

During flights at high altitude, this cabin pressure is normally set to 8,000 feet.

Pressurization Emergencies

Loss of cabin Pressure 

Three categories:

1. Slow Decompression: the most hazardous since it is hard to detect. The primary danger is hypoxia. Quick, proper utilization of oxygen equipment is necessary to avoid unconsciousness.

2. Rapid Decompression: A change in cabin pressure in which the lungs decompress faster than the cabin.

3. Explosive Decompression: A change in cabin pressure faster than the lungs can decompress, possibly resulting in lung damage.

Explosive Decompression:

United Flight 811