What altitude necessitates the use of supplemental oxygen if flight exceeds 30 minutes?

The requirement for supplemental oxygen when flying at higher altitudes is based on regulations set forth to ensure pilot and passenger safety. When flight exceeds 30 minutes at altitudes above 12,500 feet MSL (Mean Sea Level), the use of supplemental oxygen becomes mandatory. This is because, at these altitudes, the partial pressure of oxygen decreases, leading to a significant risk of hypoxia, which is a condition where the body does not receive enough oxygen.

At and above this altitude, even well-conditioned individuals can experience the onset of hypoxia, which can impair cognitive and motor functions necessary for safe flight. Regulations are in place to mitigate these risks, which include using supplemental oxygen for both pilots and passengers when flying for extended periods above this threshold. The choice reflecting this regulation is therefore correct.