At what cabin pressure altitude is supplemental oxygen required for flight time exceeding 30 minutes?

Supplemental oxygen is required for flight above 12,500 feet Mean Sea Level (MSL) when the duration of flight exceeds 30 minutes. This regulation is rooted in physiological considerations related to hypoxia, which is a deficiency in the amount of oxygen reaching the body's tissues.

At altitudes starting from 12,500 feet, the partial pressure of oxygen diminishes significantly, leading to potential impairments in cognitive and physical performance if oxygen is not supplemented. This requirement serves to ensure that pilots can maintain adequate physiological functioning during extended exposure to reduced atmospheric pressure.

Furthermore, while oxygen is required above 10,000 feet for flight durations longer than 30 minutes – which is more for crew health than passenger safety – the specific threshold of 12,500 feet is where regulations specifically mandate supplemental oxygen for pilots during prolonged flights. In contrast, altitude levels above 14,000 feet and 18,000 feet have defined oxygen requirements but involve different scenarios or durations than what is stipulated in the question.