What are the supplemental oxygen requirements for unpressurized aircraft?

The requirement for supplemental oxygen in unpressurized aircraft is particularly tied to specific altitudes due to physiological reasons related to oxygen availability and the risk of hypoxia. For flights above 12,500 feet, supplemental oxygen is required for pilots and crew members if they are operating for more than 30 minutes, and at 14,000 feet and higher, all crew members must have access to supplemental oxygen at all times. Furthermore, at 15,000 feet and above, passengers also need to be provided supplemental oxygen. This progressive approach ensures that as altitude increases, the risk of oxygen deprivation also raises the need for supplemental oxygen to sustain safe and effective operation of the aircraft, making option B the accurate choice regarding the requirements for unpressurized aircraft.