Final answer:
According to FAA regulations, supplemental oxygen is required for crew after 30 minutes above 12,500 feet and continuously above 14,000 feet; passengers require it above 15,000 feet. Symptoms of hypoxia can occur quickly at these altitudes.
Step-by-step explanation:
The question regarding how long you can fly above 12,000 ft without supplemental oxygen is related to aviation physiology and the effects of altitude on the body. The Federal Aviation Administration (FAA) regulations state that for flights above 12,500 feet up to and including 14,000 feet MSL, supplemental oxygen must be used by the required minimum flight crew for that portion of the flight at those altitudes that is of more than 30 minutes duration; and for flights above 14,000 feet MSL, the crew must use oxygen at all times. For passengers, the regulations require that there must be an oxygen supply sufficient for each occupant of the aircraft to use when the cabin pressure altitudes are above 15,000 feet MSL. Typically, symptoms of hypoxia can occur under 30 minutes without supplemental oxygen at altitudes above 12,000 feet, which is why regulations mandate oxygen usage to prevent potential health risks.