Supplemental oxygen requirements for pressurized cabin airplanes: Reciprocating engine powered airplanes

This regulation sets oxygen requirements for Part 121 airlines operating reciprocating engine airplanes with pressurized cabins, in case the pressurization system fails.

For crewmembers: Above 10,000 feet, airlines must provide oxygen for the entire flight at those altitudes. Flight deck crew need at least a two-hour supply—enough for an emergency descent from maximum altitude to 10,000 feet in ten minutes, plus 110 minutes at 10,000 feet.

For passengers: Above 8,000 feet, requirements depend on the airplane's ability to descend quickly and the altitudes flown:

• If the airplane can descend to 14,000 feet within four minutes and stays below FL250, only 10% of passengers need 30 minutes of oxygen
• If it cannot descend that quickly, or operates above FL250, more extensive oxygen supplies are required following the standards in §121.327

The regulation assumes the failure happens at the worst possible time and that the airplane will descend safely while respecting terrain and operating limits.

*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.*