Definition
A federal regulation in Title 14 of the Code of Federal Regulations that sets the supplemental oxygen requirements for flight crew and passengers in unpressurized aircraft. It requires the required minimum flight crew to use supplemental oxygen for any portion of a flight at cabin pressure altitudes above 12,500 feet MSL up to and including 14,000 feet MSL that lasts more than 30 minutes, requires continuous use by the required minimum flight crew above 14,000 feet MSL, and requires that supplemental oxygen be provided to each occupant above 15,000 feet MSL.
Plain English
The rule that tells pilots when they must start using oxygen as they fly higher. Above about 12,500 feet for long enough, the crew must use it; above 14,000 feet they must use it the whole time; and above 15,000 feet everyone on board must be given oxygen.
Context Anchor
Seen in ground training when discussing high-altitude flight, pressurized aircraft, oxygen planning, and the risk of not getting enough oxygen in flight.
Derivation
14 CFR means Title 14 of the Code of Federal Regulations -- the section of U.S. federal law dealing with aeronautics and space. Part 91 covers general operating and flight rules for civil aircraft, and section 91.211 is the specific paragraph within that part dealing with supplemental oxygen. The numbering tells you exactly where to find it: Title 14, Part 91, Section 211.
Why Pilots Care
Compliance prevents hypoxia and meets FAA legal requirements for flights that reach higher altitudes.
Grounding Statement
At higher altitudes, the body can become short of oxygen before the pilot feels clearly unsafe, so this rule sets firm oxygen requirements instead of leaving it to guesswork.
Intuition Check
Do not treat 14 CFR part 91, section 91.211 as advice or a training suggestion. It is a specific federal regulation that pilots must follow when its conditions apply.
Example Sentence 1
Planning a cross-country at 13,500 feet MSL, the pilot reviewed 14 CFR part 91, section 91.211 and confirmed the trip leg would stay under 30 minutes at that altitude.
Example Sentence 2
During preflight planning the pilot confirmed that the aircraft oxygen system met the standards in 14 CFR part 91, section 91.211.