Oxygen Systems

[Ref. Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 7-37, 7-38, 7-39]

To prevent hypoxia, crew and passengers use oxygen systems, in conjunction with pressurization systems. An oxygen system consists of a mask/cannula and a regulator that supplies a flow of oxygen dependent upon cabin altitude.


Regulations about oxygen systems

In the US, regulations require flight crews should have and use supplemental oxygen:

  • after 30 mins exposure to cabin pressure altitudes between 12,500 and 14,000 feet;
  • immediately upon exposure to cabin pressure altitudes  above 14,000 feet;

In the US, regulations require aircraft occupant (passengers) should have and use supplemental oxygen:

  • immediately upon exposure to cabin pressure altitudes above 15,000 feet 

For optimum protection, pilots are encouraged to use supplemental oxygen above 10,000 feet cabin altitude during the day and above 5,000 feet at night.


Crew masks v.s Passenger mask

Crew masks are fitted to the user’s face with a minimum of leakage and usually contain a microphone. Most masks are the oronasal type – covers only the mouth and nose.

Passenger mask may be a simple, cup-shaped rubber molding sufficiently flexible for most of the passenger’s face.


Types of Oxygen Systems

  1. Diluter-Demand Oxygen Systems
    • supply oxygen only when the user inhales
  2. Pressure-Demand Oxygen Systems
    • oxygen is supplied to the mask under pressure  – provide a positive pressure application of oxygen to the mask
  3. Continuous-Flow Oxygen System
    • usually provided for passengers
    • typically has a reservoir bag that collects oxygen when the mask user is exhaling – allows a higher aspiratory flow rate during the inhalation cycle, which reduces the amount of air dilution
  4. Electrical Pulse-Demand Oxygen System
    • deliver oxygen by detecting an individual’s inhalation effort

As we can observe, all four types of oxygen systems have certain features to make sure the oxygen are delivered to users efficiently.


Operations of Oxygen Systems

Pilots should be aware of the danger of fire when using oxygen.

Also, before each flight, the pilot should thoroughly inspect and test all oxygen equipment. The mask should be donned and the system should be tested.


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