What is the maximum altitude at which supplemental oxygen is mandatory for unpressurized aircraft?

Supplemental oxygen becomes mandatory in unpressurized aircraft once the aircraft is flying at altitudes of 14,000 feet and above. At this altitude, pilots and passengers are at increased risk for hypoxia due to the decrease in atmospheric pressure, which reduces the amount of available oxygen.

The limit is established to ensure safety and minimize the onset of physiological effects that can impair flying ability. Oxygen must be used by airline crew members during flight above 10,000 feet when operating for more than 30 minutes, and the requirement is stricter at 14,000 feet, where continuous use of supplemental oxygen becomes necessary.

This regulation aims to protect pilots and passengers from the adverse effects of reduced oxygen levels, emphasizing the importance of maintaining adequate oxygen supply during flight at high altitudes.