At what altitude must each occupant have oxygen on board an aircraft?

The correct altitude where each occupant on an aircraft must have oxygen on board is 15,000 feet. This rule is established by aviation regulations to ensure the safety of passengers and crew at higher altitudes where the atmosphere contains less oxygen. At 15,000 feet and above, the risk of hypoxia—an inadequate supply of oxygen to the body—increases significantly, requiring supplemental oxygen for passengers as a precautionary measure.

Oxygen requirements can differ at various altitudes for different purposes, and other options indicate altitudes where regulations may suggest or mandate partial use of supplemental oxygen but do not specifically require it for every occupant. Understanding these altitude thresholds is crucial for ensuring that safety protocols are properly followed in aviation operations.