Definition
The section of Title 14 of the Code of Federal Regulations (14 CFR Part 91) that sets the rules for supplemental oxygen use by flight crew and passengers in unpressurized aircraft. It specifies the cabin pressure altitudes at which oxygen must be available and used, including required crew use above 12,500 feet MSL after 30 minutes, required crew use at all times above 14,000 feet MSL, and the requirement that oxygen be provided to each occupant above 15,000 feet MSL.
Plain English
It is the FAA rule that says when pilots and passengers must use oxygen at high altitudes. The higher you fly without a pressurized cabin, the more strict the oxygen requirements become.
Context Anchor
Seen in ground training, high-altitude operations, and preflight planning when deciding whether an oxygen system is required for a planned flight.
Why Pilots Care
Knowing this section prevents inadvertent hypoxia and keeps the flight legal.
Grounding Statement
As the aircraft climbs, the air effectively available to breathe becomes thinner, so the regulation sets altitude points where oxygen must be used or available.
Intuition Check
Do not read “section 91.211” as a checklist step or training section. Here it means a specific FAA legal rule: Part 91, section 211, covering supplemental oxygen.
Example Sentence 1
Before the cross-country flight at 13,500 feet MSL, the pilot reviewed section 91.211 to confirm how long the crew could legally fly at that altitude without oxygen.
Example Sentence 2
During the preflight briefing the pilot confirmed the oxygen requirements stated in section 91.211.