Pilot requirements: Use of oxygen

This regulation sets oxygen requirements for pilots operating under Part 135.

Unpressurized aircraft: Pilots must use oxygen continuously above 12,000 feet MSL, and between 10,000-12,000 feet MSL if flying at those altitudes for more than 30 minutes.

Pressurized aircraft: If cabin pressure altitude exceeds 10,000 feet, follow the unpressurized rules. At altitudes above 25,000 feet MSL, unless pilots have quick-donning masks, at least one pilot must wear a secured oxygen mask (that supplies oxygen continuously or automatically above 12,000 feet cabin altitude), while other pilots must have masks immediately accessible. Above 35,000 feet MSL, one pilot must always wear a secured mask. If one pilot leaves the controls above 25,000 feet, the remaining pilot must don their oxygen mask until the other returns.

These requirements protect pilots from hypoxia, ensuring they remain alert and capable of controlling the aircraft at high altitudes.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*