Oxygen Systems in Aircraft

Overview of Aircraft Oxygen Systems

Modern pressurised aircraft are equipped with two independent oxygen systems: one dedicated to the flight crew and another for passengers. The crew system always uses gaseous oxygen stored in high-pressure cylinders, while passenger systems may use either gaseous oxygen or chemical oxygen generators, depending on the aircraft type and certification requirements.

Crew Oxygen Systems

Crew oxygen systems are designed for reliability and flexibility. Gaseous oxygen is delivered through masks that offer different modes:

• Normal (Diluter Demand): Mixes oxygen with cabin air, increasing oxygen proportion as cabin altitude rises.
• 100% Oxygen: Delivers pure oxygen, typically selected at higher altitudes or during smoke/fume events.
• Emergency: Provides positive pressure oxygen for maximum protection, especially in smoke or contaminated environments.

Passenger Oxygen Systems

Passenger oxygen is supplied by either fixed gaseous systems or chemical oxygen generators:

• Gaseous Systems: Use pressurised cylinders, similar to crew systems, but are heavier and more complex.
• Chemical Oxygen Generators: Activated automatically or manually, these devices produce oxygen through a chemical reaction, supplying continuous flow for a set duration (usually around 15 minutes).

Passenger masks deploy automatically if cabin pressure drops below a safe threshold, or can be released manually by the crew. Once pulled, the mask activates the oxygen flow—either by triggering the chemical generator or opening the flow from the cylinder.

Portable Oxygen Systems

Portable bottles (walk-around sets) and smoke hoods are essential for mobility and emergency response. Walk-around bottles allow crew to move throughout the cabin while breathing oxygen, with selectable flow rates for different situations. Smoke hoods combine a portable oxygen supply with respiratory and eye protection, used mainly for firefighting or smoke-filled environments.

Safety Considerations

Oxygen systems must never come into contact with grease or oil, as these substances can cause violent reactions, including fires or explosions. All maintenance and operation must be performed with extreme care, and smoking is strictly prohibited near oxygen equipment.

Capacity and Flow Regulation

Gaseous systems offer adjustable flow and large capacity but are heavier. Chemical generators are lighter and simpler but provide a fixed, non-adjustable flow for a limited time.

First Aid Oxygen

Aircraft carry medical-grade portable oxygen for passenger emergencies. Regulations specify minimum quantities based on passenger numbers and expected duration above 8,000 feet cabin altitude.