Oxygen System — Aircraft systems that provide supplemental oxygen to crew and passengers at high altitude.

Oxygen Systems in aircraft provide supplemental breathing oxygen when cabin altitude exceeds safe levels, either during normal high-altitude operations or during cabin depressurization emergencies.

• Flight crew oxygen: Gaseous oxygen in high-pressure cylinders, delivered via diluter-demand or pressure-demand masks — available for entire flight duration
• Passenger chemical generators: Sodium chlorate 'candles' that generate oxygen when activated — provide 12–22 minutes of oxygen (enough for emergency descent)
• Portable oxygen bottles: For cabin crew use, first aid, and walk-around
• Activation: Passenger masks deploy automatically when cabin altitude exceeds 14,000 ft
• Crew must don oxygen masks within seconds at cabin altitudes above 10,000 ft
• Above FL410, one crew member must wear an oxygen mask at all times