What are the requirements for supplemental oxygen under FAR regulations?

The correct answer highlights an important safety regulation regarding supplemental oxygen requirements for pilots and passengers. According to the Federal Aviation Regulations, when operating above 12,500 feet Mean Sea Level (MSL), supplemental oxygen must be provided to pilots and crew members if they will be at that altitude for more than 30 minutes. This regulation is in place to mitigate the effects of hypoxia, which can occur due to reduced oxygen pressure at higher altitudes.

Understanding this requirement emphasizes the importance of ensuring that all personnel on board are adequately equipped to handle the physiological challenges that can arise during flight in decreased atmospheric pressure environments. The 30-minute duration is specifically noted as a critical threshold, as even short exposure can lead to performance degradation and impaired decision-making.

Other options present conditions that either do not align with the regulations or represent less comprehensive requirements. For instance, while supplemental oxygen is required above 10,000 feet, it is not mandatory for all flights at that altitude, just above 12,500 feet for extended periods. Hence, option C encapsulates the precise regulation necessary to ensure safety in higher altitude operations.