Pilot Counsel

Supplemental oxygen

June 1, 2001

As general aviation pilots, we are charged with knowing the regulatory requirements for supplemental oxygen aboard the aircraft that we fly. (Airliners and some other commercial aircraft have stricter requirements.) The requirements are spelled out in FAR 91.211. This regulation could be complicated, depending on the particular aircraft. It is certainly a lot easier, and more practical, to learn and remember the requirements that apply to the particular aircraft we fly. After all, why make knowing the requirements unnecessarily harder (unless we are preparing for an FAA test)?

So, for purposes of reviewing this regulation we can categorize the aircraft as either an unpressurized aircraft that does not carry supplemental oxygen, an unpressurized aircraft that has supplemental oxygen, or a pressurized aircraft. Then you can concentrate on the part of the regulation that applies to your flying.

Unpressurized aircraft — no oxygen

For anyone operating an unpressurized aircraft that does not carry supplemental oxygen, which constitutes the majority of the general aviation fleet, the rule is relatively simple. The key altitude is 12,500 feet mean sea level (msl). There is no regulatory requirement for supplemental oxygen at or below that key altitude (though there could be good physiological reasons why a pilot would want to use oxygen below that altitude).

The regulation contains some leeway, just in case we need a little time above that key altitude to get over some weather, for example, or to maintain VFR cloud clearance. It provides that an aircraft may be operated above 12,500 feet msl for up to 30 minutes, free of any supplemental-oxygen requirement. However, that is a very limited exception, and any more than 30 minutes' flight above that key altitude triggers the requirement for supplemental oxygen, as we will explain.

Unpressurized aircraft — oxygen

Above the key altitude of 12,500 feet msl in an unpressurized aircraft with supplemental oxygen — installed or portable — we can, of course, utilize the oxygen to meet the requirements. The requirements above this altitude vary depending on whether a person is a required flight crewmember or merely another occupant. And they vary depending on additional key altitudes, i.e., "above 14,000 feet msl" and "above 15,000 feet msl."

A person who is a "required minimum flight crew" member — in other words, the pilot in command of a typical light general aviation aircraft — must have available and use supplemental oxygen for any part of the flight above 12,500 feet msl that is longer than 30 minutes' duration. Above 14,000 feet msl, we lose the 30-minute grace period. There, the "required minimum flight crew" must have available and use supplemental oxygen during the entire flight time above the key altitude of 14,000 feet msl.

What about occupants of the aircraft who are not required flight crewmembers? Passengers? At or below 15,000 feet msl, the pilot in command need not ensure that occupants, other than the required flight crew, have supplemental oxygen available to them. That changes above 15,000 feet msl. There, each occupant of the aircraft must be provided with supplemental oxygen. Notice that the pilot in command is responsible for ensuring that supplemental oxygen is available to the other occupants, but he is not responsible for ensuring that the other occupants use the oxygen.

Pressurized cabin aircraft

As more pressurized aircraft are introduced into the general aviation fleet, this part of the regulation gains importance. It is the more complicated part of the regulation.

Pressurized aircraft have special requirements related specifically to pressurized cabin aircraft, and, in addition, have the above requirements that relate both to pressurized and unpressurized aircraft. The key altitudes related to the special requirements for pressurized aircraft only are "above flight level 250" and "above flight level 350."

But before we get to the special requirements for pressurized aircraft only, in a pressurized aircraft the requirements that apply to unpressurized aircraft still apply, depending on the pressure altitude of the cabin. If the aircraft is able to maintain cabin altitudes at or below the appropriate key altitudes mentioned above, there is no additional requirement for the availability or use of supplemental oxygen by the flight crew or other occupants. However, if the cabin pressure is above an altitude of 12,500 feet msl in a pressurized cabin aircraft, the minimum flight crew must have available and use supplemental oxygen (with the same exception for any portion of the flight of 30 minutes or less, at or below 14,000 feet msl).

Now to the special requirements specifically for pressurized aircraft that are operated above the key altitudes of FL250 and FL350.

At altitudes above FL250 there must be at least a 10-minute supply of supplemental oxygen available for each occupant of the aircraft, including flight crewmembers. This reserve is required in the event of a descent because of a loss of cabin pressurization. This minimum supply is in addition to the oxygen that may be necessary to meet the above requirements common to both pressurized and unpressurized aircraft.

Aircraft operating at altitudes above FL350 are usually certificated to require more than one pilot. However, we are seeing more aircraft certificated for single-pilot operation. At altitudes above FL350, one pilot (maybe the only required pilot) at the controls is required to wear and use an oxygen mask at all times above that altitude. The mask must be secured and sealed.

If there are two pilots at the controls and each has a quick-donning type of oxygen mask available, neither pilot need wear the oxygen mask. This exception does not apply when one pilot leaves the controls of the aircraft for any reason. Then, when operating at altitudes above FL350, the remaining pilot at the controls must put on and use an oxygen mask until the other pilot has returned to that crewmember's station.

That's FAR 91.211. You can get the flavor of the regulatory scheme by reading all of it. You should know thoroughly the parts that apply to your flying.