FAR 91.211 — Supplemental Oxygen
FAR 91.211 explains when pilots and passengers need supplemental oxygen, including altitude thresholds, pressurized cabin rules, and FL350+ mask requirements.
In Plain English
FAR 91.211 sets the rules for when supplemental oxygen must be available and used in U.S.-registered civil aircraft. The thresholds are based on cabin pressure altitude (not just aircraft altitude), which matters because hypoxia can sneak up on you long before you feel it.
For unpressurized operations:
- 12,500 ft to 14,000 ft MSL: The required minimum flight crew must use oxygen for any portion of flight at these altitudes lasting more than 30 minutes.
- Above 14,000 ft MSL: The required minimum flight crew must use oxygen the entire time at those altitudes.
- Above 15,000 ft MSL: Every occupant (including passengers) must be provided with supplemental oxygen.
For pressurized aircraft:
- Above FL250: A 10-minute backup supply must be available for each occupant in case of decompression.
- Above FL350: One pilot at the controls must wear and use an oxygen mask, unless there are two pilots and both have quick-donning masks (one-hand, 5-second don) — then masks aren't required up to FL410.
- If one pilot leaves the controls above FL350, the remaining pilot must put on and use an oxygen mask until the other pilot returns.
Regulation Text
14 CFR § 91.211§ 91.211 Supplemental oxygen.
(a)No person may operate a civil aircraft of U.S. registry—
(1) At cabin pressure altitudes above 12,500 feet (MSL) up to and including 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration;
(2) At cabin pressure altitudes above 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen during the entire flight time at those altitudes; and
(3) At cabin pressure altitudes above 15,000 feet (MSL) unless each occupant of the aircraft is provided with supplemental oxygen.
(b)(1) No person may operate a civil aircraft of U.S. registry with a pressurized cabin—
(i) At flight altitudes above flight level 250 unless at least a 10-minute supply of supplemental oxygen, in addition to any oxygen required to satisfy paragraph (a) of this section, is available for each occupant of the aircraft for use in the event that a descent is necessitated by loss of cabin pressurization; and
(ii) At flight altitudes above flight level 350 unless one pilot at the controls of the airplane is wearing and using an oxygen mask that is secured and sealed and that either supplies oxygen at all times or automatically supplies oxygen whenever the cabin pressure altitude of the airplane exceeds 14,000 feet (MSL), except that the one pilot need not wear and use an oxygen mask while at or below flight level 410 if there are two pilots at the controls and each pilot has a quick-donning type of oxygen mask that can be placed on the face with one hand from the ready position within 5 seconds, supplying oxygen and properly secured and sealed.
(2) Notwithstanding paragraph (b)(1)(ii) of this section, if for any reason at any time it is necessary for one pilot to leave the controls of the aircraft when operating at flight altitudes above flight level 350, the remaining pilot at the controls shall put on and use an oxygen mask until the other pilot has returned to that crewmember's station.
Oral Exam Questions a DPE Might Ask
Q1When is supplemental oxygen required for the flight crew in an unpressurized aircraft?
Per FAR 91.211, the required minimum flight crew must use oxygen above 12,500 ft MSL up to 14,000 ft MSL for any portion exceeding 30 minutes, and continuously at any altitude above 14,000 ft MSL.
Q2At what cabin pressure altitude must oxygen be provided to passengers, and how does that differ from the crew requirement?
Under FAR 91.211(a)(3), each occupant — including passengers — must be provided with supplemental oxygen above 15,000 ft MSL, whereas the crew oxygen-use requirements begin at 12,500 ft MSL.
Q3In a pressurized aircraft above FL350, when can the pilot at the controls go without wearing an oxygen mask?
FAR 91.211(b)(1)(ii) allows the pilot to forgo wearing the mask at or below FL410 only if there are two pilots at the controls and each has a quick-donning mask that can be donned with one hand in 5 seconds.
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Related Sections in Part 91