Pilot Counsel:

Supplemental oxygen reviewed

February 1, 2011

Legal questions from the FAR Refresher at AOPA Aviation Summit provide insight into what members would like covered here. Several questions suggested a review of FAR 91.211, which sets out the regulatory requirements for supplemental oxygen in private, noncommercial operations. Perhaps it goes without saying that this regulation recognizes that the time of useful consciousness of an individual drops insidiously as altitude increases. These are vital minimum requirements. (See “ Safety Pilot Landmark Accidents: Into Thin Air,”.) The requirements are more understandable if we deal separately with an unpressurized aircraft that does not carry supplemental oxygen; an unpressurized aircraft that has supplemental oxygen; and a pressurized aircraft.

Unpressurized aircraft, no oxygen

For anyone operating an unpressurized aircraft that does not carry supplemental oxygen, the rule is relatively simple. The key altitude is 12,500 feet msl. There is no regulatory requirement for supplemental oxygen at or below that key altitude (although there could well be good physiological reasons why a pilot would want to use oxygen below that altitude).

If we could use a little time above that key altitude—for example, to get over some weather or to maintain VFR cloud clearance—the regulation provides that an aircraft may be operated above 12,500 feet msl (up to 14,000 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 spent above that key altitude triggers the requirement for supplemental oxygen.

Unpressurized aircraft, oxygen

Above the key altitude of 12,500 feet msl in an unpressurized aircraft with supplemental oxygen (installed or portable), the requirements vary depending on whether a person is a required flight crewmember or merely another occupant. And, they vary depending on two other key altitudes: “above 14,000 feet msl” and “above 15,000 feet msl.”

A person who is a “required minimum flight crew” member (the pilot in command of a typical light GA 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 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 passengers? At or below 15,000 feet msl, the pilot in command need not assure 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 must assure that supplemental oxygen is available to the other occupants, but the pilot in command is not required by regulation to assure that the other occupants use the oxygen.

Pressurized-cabin aircraft

Pressurized aircraft have both special requirements related specifically to pressurized-cabin aircraft, and, in addition, have the requirements that relate to both pressurized and unpressurized aircraft. The key altitudes related to the special requirements for pressurized aircraft only are “above FL250” and “above FL350.”

In a pressurized aircraft, the above 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 -use of supplemental oxygen by the flight crew or other occupants. However, in a pressurized-cabin aircraft, if the cabin pressure is above an altitude of 12,500 feet msl, the minimum flight crew must have available and use supplemental oxygen (with the same exception for a maximum of 30 minutes, 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 flight altitudes above FL250 there must be a 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 flight altitudes above FL350 are usually certificated to require more than one pilot. However, more aircraft are being certificated for single-pilot operation. At flight altitudes above FL350, one pilot (maybe the only required pilot) at the controls is required to wear and use an oxygen mask. 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.

That’s FAR 91.211 in a nutshell.

John S. Yodice is the owner of a Cessna 310 based at Frederick, Maryland ( FDK).

John S. Yodice

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