Oxygen System



The oxygen system in any airline aircraft is actually comprised of three separate systems - the passenger, the flight crew, and the portable oxygen systems.


The passenger system is supplied by individual chemical generators located at each Passenger Service Unit (PSU). For example, in the Boeing 737 aircraft these PSUs' contain four continuous flow masks that are connected to each generator. A generator with two masks is located above each flight attendant seat and in each lavatory. The passenger system is activated two ways. It is activated automatically when the cabin altitude goes above 14,000 feet (usual cabin altitude can be 6000 to 8000 feet). It can also be activated by the pilots in the cockpit when they flip a switch. In either case, masks will drop down from the PSU. The oxygen generators are activated when any mask in the Unit is pulled down. Pulling one mask down causes all of the masks to come down and 100% oxygen flows to all of the masks. A green flow indicator within your oxygen hose is visible whenever oxygen is flowing to the mask. Your oxygen will last approximately 12 minutes and can't be shut off.

Oxygen Mask Safety Instructions with female demonstrations
Oxygen Mask Safety Instructions


The flight crew system is supplied by a separate cylinder usually located in the forward cargo compartment. There is a thermal discharge relief valve that is connected to this cylinder to prevent an overheat condition. If this valve releases pressure due to possible overheat, a disc will blow out and vent the excess pressure. On the Boeing 737, this disc is green in color and is located on the outside of the forward, right fuselage. This is one of the items the pilots will check on their "walk-around". It uses quick-donning masks at each pilots' position. There is also one at the observer's station (jumpseat). When pulled out of their respective boxes at each pilot position, the masks can be fitted and formed around your face by air that enters a harness comprised of small diameter and flexible tubes. A microphone is installed so that the pilots can talk to each other and on the radio while wearing the oxygen mask.

Pilot’s Oxygen Masks are quick-donning masks at each pilots' position Crew Oxygen Masks located in the forward cargo compartment
Pilot’s Oxygen Mask Crew Oxygen Masks


The portable system is comprised of the passenger portable system and the flight crew portable system. The passenger system has several (depending on the size of your aircraft) bottles and connected masks located throughout the cabin, mainly used for first aid. The flight crew system usually has a full face mask and bottle in the cockpit.


All oxygen systems can be checked to make sure they are working properly and have the sufficient amount of pressure and quantity. This is one of the items your crew will verify on their preflight checks.


Oxygen System back to Preflight

Oxygen System back to My Airline Flight