Under what conditions can a pilot fly if above 14,000' MSL without supplemental oxygen?

A pilot cannot fly above 14,000 feet Mean Sea Level (MSL) without supplemental oxygen because this altitude requires oxygen to ensure adequate cognitive and physical performance due to reduced atmospheric pressure and decreased oxygen levels. Regulations state that pilots must use supplemental oxygen if they are above this altitude for extended periods, which is generally defined as more than 30 minutes.

This requirement is in place to prevent hypoxia, a condition that occurs when the body doesn’t receive enough oxygen, which can impair decision-making and reaction times. Therefore, the answer relies on the understanding of aviation regulations concerning oxygen use, indicating that it is not permitted to operate an aircraft without supplemental oxygen at these altitudes under normal circumstances.