At what altitude must crew members use oxygen at all times?

Crew members must use oxygen at all times when operating at or above 14,000 feet. The Federal Aviation Administration (FAA) regulations state that this requirement is in place to ensure the safety of the flight crew, as the reduced atmospheric pressure at higher altitudes can lead to hypoxia—a condition where the body does not get enough oxygen.

While it is true that supplemental oxygen becomes necessary at lower altitudes for passenger use (12,500 feet for more than 30 minutes and 14,000 feet for any duration of flight), the constant use of oxygen for crew members begins specifically at 14,000 feet. This regulation emphasizes the importance of maintaining alertness and operational efficiency for those controlling the aircraft at these elevations. Using oxygen aids in preventing impairment that might occur due to diminished oxygen availability, thus ensuring both safe operations and the health of the crew during high-altitude flights.