If you are not using supplemental oxygen what are the restrictions for between 10,000 - 12,500' MSL?

The correct response is based on regulations regarding the use of supplemental oxygen at altitudes between 10,000 and 12,500 feet Mean Sea Level (MSL). At these altitudes, if the pilot is not using supplemental oxygen, there are specific time limits imposed to ensure safety.

Flying for more than one hour under Instrument Meteorological Conditions (IMC) or at night without supplemental oxygen poses significant risks because the likelihood of hypoxia increases, which can impair cognitive and physical functions. Therefore, the rule specifies that pilots must not exceed one hour of operation in these conditions at altitudes between 10,000 and 12,500 feet MSL if they are not using supplemental oxygen.

This regulation is designed to protect the pilot and ensure safe flight operations, particularly since the risk of hypoxia becomes more pronounced as altitude increases, especially when transitioning into IMC or flying at night when visibility and situational awareness may already be compromised.