We are at exactly 12,500 feet for two hours. Does the crew need oxygen?

Section 91.211(a)(1) begins above 12,500 feet MSL. At exactly 12,500, that paragraph has not started. The next foot above 12,500 is in the band.

We are at exactly 14,000 feet for 45 minutes. Which paragraph applies?

Paragraph (a)(1) runs up to and including 14,000 feet MSL. At exactly 14,000 you are still in the “more than 30 minutes” crew rule, not the “entire flight time” rule. The entire-time rule in (a)(2) is above 14,000 feet MSL.

Above 15,000 feet, do passengers have to be using the oxygen?

Paragraph (a)(3) says each occupant must be provided with supplemental oxygen. It does not say each occupant must be using it. The required minimum flight crew, above 14,000 feet MSL, must be provided with it and must use it for the entire time at those altitudes.

The airplane is unpressurized. Is cabin pressure altitude different from the altitude I read?

In an unpressurized cabin, cabin pressure altitude is the altitude the airplane is flying. The regulation still names cabin pressure altitude so a pressurized airplane is measured by the cabin, not by the flight level, for paragraph (a). Paragraph (b) adds separate rules that are written in flight altitudes and flight levels.

What does 91.211 require of a pressurized airplane at the flight levels?

Above flight level 250, 91.211(b)(1)(i) requires at least a 10-minute supply of supplemental oxygen for each occupant, in addition to any oxygen paragraph (a) requires, for a descent caused by loss of cabin pressurization. Above flight level 350, one pilot at the controls must wear and use a secured, sealed oxygen mask that supplies oxygen at all times or automatically when cabin pressure altitude exceeds 14,000 feet MSL. At or below flight level 410 that pilot need not wear the mask if two pilots are at the controls and each has a quick-donning mask that can be placed on the face with one hand from the ready position within 5 seconds. If one pilot leaves the controls above flight level 350, the pilot who remains puts on and uses a mask until the other pilot is back.

When is supplemental oxygen required?

Q: When is supplemental oxygen required?

14 CFR 91.211 uses cabin pressure altitude: crew oxygen above 12,500 feet MSL up to and including 14,000 for more than 30 minutes, crew at all times above 14,000, and oxygen for each occupant above 15,000.

14 CFR 91.211(a) uses cabin pressure altitude, not “indicated altitude” as a separate idea. For a civil aircraft of U.S. registry: above 12,500 feet MSL up to and including 14,000 feet MSL, the required minimum flight crew must be provided with and use supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration. Above 14,000 feet MSL, that crew must use it the entire time at those altitudes. Above 15,000 feet MSL, each occupant must be provided with supplemental oxygen.

Study aid, not legal advice. Regulations, the AIM, and handbook editions change. Check the current text and confirm anything that affects a flight or a checkride with your CFI.

The three altitudes in paragraph (a)

Section 91.211(a) applies when you operate a civil aircraft of U.S. registry. The thresholds are cabin pressure altitudes:

Above 12,500 feet MSL up to and including 14,000 feet MSL. The required minimum flight crew must be provided with and use supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration. A brief climb through the band is not the same as time in the band that runs past 30 minutes. The rule’s own words are the standard to quote: oxygen for the part of the flight at those altitudes that is of more than 30 minutes duration.
Above 14,000 feet MSL. The required minimum flight crew must be provided with and use supplemental oxygen during the entire flight time at those altitudes. There is no 30-minute exception once you are above 14,000.
Above 15,000 feet MSL. Each occupant must be provided with supplemental oxygen. “Provided” is the verb in the regulation. The crew-use requirement from the line above is still in force for the required minimum flight crew.

Two boundaries are easy to slide. The 30-minute band starts above 12,500, not at 12,500, and it includes 14,000. The continuous crew requirement starts above 14,000. The occupant requirement starts above 15,000.

Pressurized cabins, paragraph (b)

Paragraph (a) can apply to a pressurized airplane when the cabin altitude is high, including after a pressurization failure. Paragraph (b) adds rules written in flight altitude. Above FL250, each occupant needs at least a 10-minute supply in addition to paragraph (a), for a descent after loss of pressurization. Above FL350, the mask rule for a pilot at the controls applies, with the two-pilot quick-donning exception at or below FL410, and the rule that the remaining pilot dons a mask if the other pilot leaves the controls.

A private pilot oral on a light unpressurized airplane usually stops at paragraph (a). If the examiner asks about a pressurized cabin, answer from paragraph (b) rather than stretching the 12,500-foot rule up to the flight levels.

High cabin altitudes are also a performance and human-factors topic. Density altitude, which is a different idea, is on the density altitude page. Day 6 of the oral checklist is performance, systems, and the human-factors task that follows.

Common examiner follow-ups

We are at exactly 12,500 feet for two hours. Does the crew need oxygen?: Section 91.211(a)(1) begins above 12,500 feet MSL. At exactly 12,500, that paragraph has not started. The next foot above 12,500 is in the band.
We are at exactly 14,000 feet for 45 minutes. Which paragraph applies?: Paragraph (a)(1) runs up to and including 14,000 feet MSL. At exactly 14,000 you are still in the “more than 30 minutes” crew rule, not the “entire flight time” rule. The entire-time rule in (a)(2) is above 14,000 feet MSL.
Above 15,000 feet, do passengers have to be using the oxygen?: Paragraph (a)(3) says each occupant must be provided with supplemental oxygen. It does not say each occupant must be using it. The required minimum flight crew, above 14,000 feet MSL, must be provided with it and must use it for the entire time at those altitudes.
The airplane is unpressurized. Is cabin pressure altitude different from the altitude I read?: In an unpressurized cabin, cabin pressure altitude is the altitude the airplane is flying. The regulation still names cabin pressure altitude so a pressurized airplane is measured by the cabin, not by the flight level, for paragraph (a). Paragraph (b) adds separate rules that are written in flight altitudes and flight levels.
What does 91.211 require of a pressurized airplane at the flight levels?: Above flight level 250, 91.211(b)(1)(i) requires at least a 10-minute supply of supplemental oxygen for each occupant, in addition to any oxygen paragraph (a) requires, for a descent caused by loss of cabin pressurization. Above flight level 350, one pilot at the controls must wear and use a secured, sealed oxygen mask that supplies oxygen at all times or automatically when cabin pressure altitude exceeds 14,000 feet MSL. At or below flight level 410 that pilot need not wear the mask if two pilots are at the controls and each has a quick-donning mask that can be placed on the face with one hand from the ready position within 5 seconds. If one pilot leaves the controls above flight level 350, the pilot who remains puts on and uses a mask until the other pilot is back.

Sources

14 CFR 91.211 — Supplemental oxygen

Checked against the eCFR, the AIM, and FAA-H-8083-25C on October 29, 2026. The eCFR is updated continuously; the link opens the current section.