At what maximum cabin altitude must passengers be provided with supplemental oxygen in an unpressurized aircraft under IFR?

In an unpressurized aircraft operating under Instrument Flight Rules (IFR), supplemental oxygen must be provided to passengers when the cabin altitude reaches 15,000 feet. This regulation is grounded in ensuring passenger safety, as oxygen levels can significantly drop in the atmosphere at high altitudes, leading to potential hypoxia—a condition that occurs when the body is deprived of adequate oxygen.

The Federal Aviation Administration (FAA) stipulates that at cabin altitudes above 15,000 feet, passengers should have supplemental oxygen readily available. While crew members have established requirements for supplemental oxygen at lower altitudes—beginning at 12,500 feet for different circumstances—most regulations focus on the cabin environment as experienced by passengers who might not be as familiar with or accustomed to altitude flying.

Providing oxygen ensures that passengers can maintain adequate health and cognitive function while flying at altitude, especially when unpressurized environments are concerned. Hence, the correct altitude for mandating supplemental oxygen for passengers in an unpressurized aircraft is indeed 15,000 feet.