Aircraft oxygen systems are designed to ensure the safety and comfort of pilots and passengers while flying at high altitudes. As the altitude increases, the atmospheric pressure drops, leading to low oxygen levels that can be insufficient for humans to breathe. Therefore, it is critical for aircraft to have reliable oxygen systems to maintain optimal oxygen levels throughout the flight.

There are three main types of aircraft oxygen systems: Continuous Flow, Diluter Demand, and Pressure Demand, each intended for varying altitudes and aircraft types. A continuous-flow oxygen system is commonly found in portable oxygen units or planes limited to around 25,000 feet, providing a constant flow of oxygen regardless of the user’s breathing patterns. Diluter demand systems, on the other hand, deliver oxygen efficiently only during inhalation, reducing waste and making them ideal for cabin altitudes up to 34,000 feet. Finally, pressure-demand systems create an airtight seal and deliver oxygen under pressure when needed, making them the preferred choice for crew members on larger transport aircraft operating at higher altitudes.

Aircraft Oxygen System Overview

Aircraft oxygen systems are essential for ensuring passengers and crew have access to supplemental oxygen at high altitudes, helping to prevent hypoxia and maintain overall safety. This section will provide a brief overview of the three primary types of aircraft oxygen systems: Continuous Flow, Diluter Demand, and Pressure Demand.

Continuous Flow

The Continuous Flow oxygen system is designed for simplicity and is most commonly found in non-pressurized aircraft and portable systems¹. Oxygen flows continuously from the storage tank, through a regulator, and to the user’s oxygen mask. This type of system is typically used at altitudes up to 28,000 feet².

Pros of Continuous Flow system:

Simple design
Cost-effective
Suited for lower altitudes

Cons of Continuous Flow system:

Wasteful, as oxygen flows constantly, even when not inhaled³
Not suited for high altitudes

Diluter Demand

The Diluter Demand system is designed to improve upon the shortcomings of the Continuous Flow system. This system delivers oxygen to the user on-demand (during inhalation) and stops the flow during exhalation⁴. Diluter-demand regulators are usually located at each crew position and can be adjusted to suit the user’s needs⁵.

Pros of Diluter Demand system:

More efficient use of oxygen
Adaptive to user’s inhalation pattern
Suitable for higher altitudes

Cons of Diluter Demand system:

More complex than Continuous Flow
May be more expensive

Pressure Demand

Finally, the Pressure Demand system is widely used in larger transport aircraft, particularly for the crew⁶. This system delivers oxygen under pressure, ensuring that the user receives adequate oxygen even at extremely high altitudes or in emergency situations like rapid decompression. Pressure-demand systems often work in conjunction with continuous-flow or diluter-demand systems for passengers⁷.

Pros of Pressure Demand system:

Delivers oxygen under pressure
Suitable for very high altitudes and emergency situations
Commonly used in large, pressurized aircraft

Cons of Pressure Demand system:

Most complex of the three options
Likely more expensive than other systems

Oxygen System Components

Gaseous Oxygen Systems

Gaseous oxygen systems are commonly used in various aircraft. They typically consist of oxygen stored in high-pressure cylinders, which is then distributed through various components, such as continuous flow oxygen masks and cannulas. These systems can be adjusted to provide the appropriate levels of oxygen based on altitude and atmospheric pressure, ensuring that pilots and passengers receive an adequate amount of oxygen.

Continuous flow system: These systems provide a constant supply of oxygen and are typically used in aircraft flying at altitudes up to 28,000 feet. As the name suggests, oxygen flow is continuous, and passengers may receive oxygen through masks or cannulas.
Regulations: Gaseous oxygen systems follow strict regulations to ensure safety, such as pressure testing for cylinders and proper storage requirements.

Chemical Oxygen Systems

Chemical oxygen systems generate oxygen through a chemical reaction, eliminating the need for cylinders. These systems tend to be lightweight and can be especially useful in emergency situations. Oxygen is generated on-demand and can be delivered through masks or cannulas. Some chemical oxygen generators are designed for single-use and must be replaced after the activation.

Liquid Oxygen Systems (LOX)

Liquid oxygen (LOX) systems store oxygen in a liquid state at extremely low temperatures. They are more compact than gaseous oxygen systems and can store a larger amount of oxygen.

LOX to Gas Conversion: When needed, the liquid oxygen is converted to a gas and supplied to masks or cannulas. This process involves a heat exchanger to allow for the necessary expansion and pressure adjustments.
Advantages: LOX systems provide a longer duration of oxygen supply compared to gaseous systems, making them suitable for long flights.

Portable Equipment

Portable oxygen equipment offers flexibility and portability for pilots and passengers who may require supplemental oxygen during flight. These systems can include a variety of components such as small cylinders, masks, cannulas, and regulators.

Continuous flow: Portable systems often utilize continuous-flow regulators, providing oxygen at a constant rate to users.
Convenience: Portable equipment allows oxygen to be easily accessible, especially in non-pressurized aircraft and during emergencies.

Oxygen Delivery Methods

In this section, we will discuss the various methods used for the delivery of oxygen in aircraft, focusing on Oxygen Masks and Cannulas, Adjustable Flow Indicators, and Plug-in Supply Sockets. We will also touch upon the different types of oxygen systems: Continuous Flow, Diluter Demand, and Pressure Demand.

Oxygen Masks and Cannulas

Oxygen Masks: These are commonly used in aircraft oxygen systems to ensure high oxygen saturation levels. Masks are typically used at higher altitudes or in emergency situations when a greater concentration of oxygen is needed. Masks are available in different designs, catering to continuous-flow oxygen systems, diluter demand systems, and pressure-demand oxygen systems.
Cannulas: These are lightweight alternatives to masks and are often used in light aircraft. Consisting of plastic tubes with small prongs that fit into your nostrils, cannulas provide a continuous flow of oxygen during flight. However, they are not suitable for use above 18,000 feet as they cannot deliver high concentrations of oxygen required at higher altitudes.

Adjustable Flow Indicators

Adjustable flow indicators are essential for monitoring and controlling the amount of oxygen being delivered to the user. They allow pilots to adjust the oxygen flow rate according to their needs, ensuring optimal oxygen saturation at all times. In a continuous-flow oxygen system, the indicators control the flow rate to all users, while in diluter demand and pressure-demand systems, individual regulators at each crew position allow for personalized adjustments.

Plug-in Supply Sockets

Plug-in supply sockets play a crucial role in making oxygen systems more accessible and efficient. They allow for the easy connection of oxygen masks or cannulas to the aircraft’s oxygen storage, making it simple to switch between users or types of oxygen delivery devices. These sockets are especially useful in military aircraft, where quick access to emergency oxygen is vital for crew safety.

Regulators and Monitoring

Oxygen systems in aircraft need reliable regulators and monitoring devices to ensure pilot and passenger safety. In this section, we will discuss diluter-demand regulators and various monitoring techniques, such as pulse oximeters and partial pressure monitoring.

Diluter-Demand Regulator

The diluter-demand regulator is a significant component in aircraft oxygen systems. It works by holding back the flow of oxygen until the user inhales through a demand-type oxygen mask. The regulator then dilutes the oxygen flow with ambient air, providing a suitable and effective mix for the user. This design compensates for the shortfalls of continuous-flow systems, which waste oxygen by providing a constant stream regardless of the user’s inhalation cycle (source). Diluter-demand regulators are typically found at each crew position in a pressurized aircraft, allowing for individual control (source).

Pulse Oximeter

A pulse oximeter is an essential monitoring tool in aircraft oxygen systems, as it non-invasively measures the percentage of hemoglobin in the bloodstream saturated with oxygen. Pilots can use this portable device to check their blood oxygen saturation levels (SpO2) periodically during a flight, ensuring safe and proper oxygen usage. Pulse oximeters have become increasingly popular due to their ease of use, portability, and affordability.

Partial Pressure Monitoring

Partial pressure monitoring is another effective method for observing oxygen levels in aircraft systems. This technique measures the partial pressure of oxygen in the breathing gas mixture, providing essential information for monitoring and adjusting the oxygen flow. Accurate partial pressure monitoring enables pilots and crew members to maintain optimal oxygen levels throughout the flight.

When it comes to oxygen system servicing, it’s crucial to follow the manufacturer’s guidelines and keep components such as 3HT bottles and filters in good working condition. Regular maintenance of these parts helps to ensure the efficient and safe operation of the aircraft’s oxygen systems.

Oxygen Storage and Cylinders

Aircraft oxygen systems ensure that pilots and passengers have the necessary breathable air at high altitudes. These systems use various types of oxygen storage methods and cylinders depending on the aircraft and specific needs. In this section, we will discuss high-pressure steel cylinders, composite cylinders, and transport category aircraft cylinders.

High-Pressure Steel Cylinders

High-pressure steel oxygen cylinders are commonly used in aircraft oxygen systems. They store oxygen at a high partial pressure, which can be reduced and regulated through a flow meter to achieve a constant or demand flow suitable for users. These cylinders are generally durable and have to undergo periodic hydrostatic tests to ensure their safety and performance.

High-pressure steel cylinders can be used in different systems such as:

Continuous Flow: Oxygen is provided to users at a constant rate from the cylinder, often utilized in non-pressurized aircraft and portable oxygen systems.
Diluter Demand: Oxygen flow is provided on-demand during inhalation, offering better efficiency than continuous flow systems.
Pressure Demand: Similar to diluter demand, but pressure is automatically adjusted depending on the altitude, thus providing the necessary oxygen pressure.

Composite Cylinders

Composite cylinders are an alternative to high-pressure steel oxygen cylinders. They are made from a combination of materials, often including carbon fiber and other lightweight components. These cylinders offer several advantages, such as being lighter than steel cylinders and having higher resistance to corrosion. They can also handle higher pressures and are becoming increasingly popular in aviation applications for portable oxygen systems.

Transport Category Aircraft Cylinders

Transport category aircraft, which typically include commercial airlines, require more extensive oxygen storage solutions. These aircraft often have built-in oxygen systems consisting of multiple cylinders and distribution systems throughout the passenger compartment. They are designed to provide oxygen to both the pilots and passengers in case of an emergency or loss of cabin pressure.

In transport category systems, the oxygen is often stored as gaseous oxygen and regulated as needed through nasal cannula or other means of delivery. These systems require proper maintenance and regular checks to ensure that the cylinders are in good condition and perform efficiently in high-altitude conditions.

Safety and Maintenance

When it comes to aircraft oxygen systems, safety and maintenance are crucial for ensuring the well-being of passengers and crew members. This section will cover a few important aspects related to safety and maintenance in the context of Continuous Flow, Diluter Demand, and Pressure Demand oxygen systems.

Decompression and Smoke Issues

Decompression incidents and smoke or fumes in the cabin are two common scenarios that may require the use of oxygen systems. In these situations, the proper functioning of the oxygen system is essential for the safety of everyone on board. To minimize the risk of complications during these critical moments, regular inspection and maintenance of the oxygen equipment is necessary.

Adjustable flow indicators can help pilots and crew members determine the appropriate oxygen flow during situations like rapid decompression or smoke-related incidents. It is important to ensure that these indicators are working correctly and are set to the correct flow rates based on the flight altitude.

Crew Member Requirements

Crew members must be familiar with the appropriate use of aviation oxygen systems to ensure the safety of passengers and themselves. This includes understanding the limitations of each system type at different flight altitudes.

For instance, Continuous Flow systems are typically used at heights of 28,000 feet and below, while Diluter Demand and Pressure Demand systems become more relevant at higher altitudes. Ensuring that crew members are aware of which system to use and how to use it accurately is essential for their safety and that of the passengers.

Hydrostatic Testing

Oxygen system cylinders are subject to periodic hydrostatic testing to ensure their structural integrity and safety. The Department of Transportation (DOT) has certain regulations in place to perform these tests, such as the DOT-E-8162 and DOT-SP-8162 certifications.

There are two main types of cylinders to consider in hydrostatic testing:

3AA: Compressed gas cylinders made of steel, which undergo testing at least once every five years.
DOT-E-8162: Composite overwrapped cylinders, tested every three years.

Both types of cylinders should be serviced at authorized and certified facilities to ensure the testing is completed in accordance with the applicable regulations.

Regulations

Aircraft oxygen systems are subject to various regulations to ensure they operate reliably and efficiently. Adhering to these regulations helps maintain the safety of passengers and crew during flights. Some common regulations related to aircraft oxygen systems include maintenance schedules, required equipment, and standards for cylinder testing.

It’s essential for aircraft operators to stay informed and up-to-date on these regulations as they can change periodically. This will ensure the proper functioning and safety of the oxygen system during flights.

By prioritizing safety and maintenance, aircraft operators can provide a safe environment for passengers and crew members while using various types of aviation oxygen systems. Regular inspections, adherence to regulations, and proper crew member training are all essential aspects of maintaining a safe and efficient oxygen system.

Advanced Features and Technology

Demand Flow Oxygen Systems

Demand flow oxygen systems are designed to provide oxygen to users only when needed, such as during inhalation. These systems can help conserve oxygen and improve overall efficiency. One example of a demand flow system is the Diluter Demand system, which combines both inhaled oxygen with cabin air to provide the appropriate partial pressure of oxygen for the user. This system works with the help of a calibrated orifice, aneroid, and pressure relief valve, which together manage the flow of oxygen.

Quick-Don Masks and Goggles

Quick-don masks and goggles are essential components of aircraft oxygen systems, ensuring that flight crews can quickly and easily access oxygen supplies in emergency situations. These masks typically have plug-in supply sockets and rebreather apparatus features, allowing for rapid deployment and connection to the aircraft’s oxygen supply. Goggles help protect crew members’ eyes from potential hazards and ensure clear visibility during an emergency.

Fingertip Pulse Oximeters

Fingertip pulse oximeters offer a simple and non-invasive way to monitor oxygen saturation levels for both flight crews and passengers. These compact devices easily clip onto a fingertip, providing real-time readings of the user’s blood oxygen levels. By using pulse oximeters, flight crews can proactively identify any potential hypoxia issues and take appropriate action to address them.

Communications

In an aircraft environment, clear and effective communication is crucial for maintaining safety and addressing situations that may arise. Incorporating reliable communication systems into aircraft oxygen equipment can be beneficial for both flight crews and passengers. This can include systems such as intercoms or the Passenger Service Unit, which allows for efficient communication between passengers and crew members, ensuring that help can be summoned when needed.

Types of Aircraft Oxygen Systems: Exploring Continuous Flow, Diluter Demand, and Pressure Demand