Private Pilot Private Practice Exam

The requirement for the use of supplemental oxygen during flight at cabin pressure altitudes between 12,500 feet MSL and 14,000 feet MSL mandates that oxygen must be used if the flight time exceeds 30 minutes at those altitudes. This is based on physiological considerations, as the risk of hypoxia increases significantly when operating above 12,500 feet.

At altitudes in this range, the partial pressure of oxygen decreases, and prolonged exposure can impair cognitive function and physical performance. Therefore, the regulation is designed to ensure safety by requiring supplemental oxygen usage for any flight exceeding 30 minutes within this altitude band. This approach allows for some degree of flexibility for flights in which the crew remains below the threshold time, ensuring that not every moment at these altitudes requires oxygen if the time is brief.

The other choices imply more restrictive or different conditions for oxygen use that do not align with established regulations regarding cabin altitude operations. Thus, the correct understanding of oxygen requirements is reflected accurately in the choice specifying that supplemental oxygen is necessary only after a flight time of 30 minutes at these altitudes.