At what maximum cabin pressure altitude may a civil aircraft of US registry operate without supplemental oxygen for each occupant?

The maximum cabin pressure altitude for a civil aircraft of US registry to operate without supplemental oxygen for each occupant is 15,000 feet MSL. This regulation is established by the Federal Aviation Administration (FAA) to ensure the safety and health of occupants during flight at high altitudes, where the availability of oxygen can significantly reduce due to lower air pressure.

At pressures above 15,000 feet, the concentration of oxygen in the atmosphere is insufficient for normal physiological function, leading to potential hypoxia, a condition arising from insufficient oxygen reaching tissues. Therefore, the FAA mandates that supplemental oxygen must be provided to all occupants if the cabin altitude exceeds this threshold.

The limits set at lower altitudes, such as 10,000 and 12,500 feet, are for specific situations related to pilot requirements. For instance, at 12,500 feet, pilots are required to use supplemental oxygen for flights exceeding 30 minutes, which emphasizes the need for oxygen awareness at these altitudes but does not necessitate its use for every occupant like at 15,000 feet.

Understanding these altitude limitations is crucial for pilots in order to ensure passenger safety and compliance with aviation regulations.