Above what altitude MSL is supplemental oxygen required for the pilot of an unpressurized aircraft?

The requirement for supplemental oxygen in unpressurized aircraft is based on the physiological effects of oxygen deprivation at higher altitudes. Specifically, pilots are required to use supplemental oxygen when operating above 14,000 feet Mean Sea Level (MSL) for extended periods.

This altitude is significant because at 14,000 feet, the partial pressure of oxygen in the atmosphere decreases, which can lead to hypoxia – a condition where the body is deprived of adequate oxygen. The regulations are designed to ensure that pilots can maintain cognitive functions and physical performance.

While oxygen use is recommended starting at 10,000 feet for flight operations lasting over 30 minutes and becomes necessary at 12,000 feet if flying above that altitude for an hour or more, the specific and mandatory requirement kicks in at 14,000 feet. Thus, the requirement at this altitude serves as a critical safety measure for pilots in unpressurized aircraft.