At what altitude must unpressurized pilots use oxygen continuously?

The requirement for unpressurized pilots to use oxygen continuously is essential for maintaining safety and awareness at higher altitudes where oxygen levels decrease. The regulations specify that pilots must use supplemental oxygen continuously when flying above 12,000 feet. Additionally, for altitudes between 10,000 feet and 12,000 feet, if the flight time at that altitude exceeds 30 minutes, continuous oxygen use is also mandated.

This means that the correct choice encompasses both scenarios: the requirement for continuous oxygen usage starting at 12,000 feet and the stipulation regarding longer flights at altitudes between 10,000 feet and 12,000 feet. By recognizing these two guidelines, pilots can ensure they are adhering to safety standards regarding oxygen use and preventing hypoxia, which could impair cognitive functions and flying capabilities.