What is a key requirement for the carriage of supplementary oxygen in aircraft?

The key requirement for the carriage of supplementary oxygen in aircraft is related to the time a passenger may be exposed to altitudes where oxygen levels are insufficient for normal physiological function. According to regulations, supplementary oxygen must be provided for passengers if the flight exceeds 30 minutes above a specific altitude, typically around 15,000 feet, where the risk of hypoxia becomes significant.

This regulation emphasizes the necessity of ensuring passenger safety during prolonged exposure to high altitudes. Passengers are at higher risk of experiencing hypoxia at these altitudes, so it is crucial that oxygen supplies are available during extended durations to mitigate health risks associated with reduced atmospheric pressure and oxygen concentration. This protective measure falls in line with broader safety protocols intended to safeguard all individuals on board during critical phases of flight.

In contrast, other considerations listed in the options relate to different altitude thresholds or crew-related requirements, which may not specifically address the same duration and altitude conditions required for passenger safety.