How long can flight crew be without supplemental oxygen on flights at 12,500 to 14,000 feet?

When operating between 12,500 and 14,000 feet, flight crew members are allowed to function without supplemental oxygen for a limited period of time, specifically up to 30 minutes. This regulation is in place due to the physiological effects of altitude on the human body; at these elevations, the partial pressure of oxygen decreases, potentially leading to hypoxia (a deficiency in the amount of oxygen reaching the tissues).

The Federal Aviation Administration (FAA) standards recognize that flight crew can safely perform their duties without supplemental oxygen for this short duration, as long as they are trained to notice and manage early symptoms of hypoxia. Beyond 30 minutes at these altitudes, supplemental oxygen becomes necessary to ensure that the crew maintains optimal performance and safety.