If one pilot leaves a pilot duty station of an aircraft when operating at altitudes above 25,000 feet MSL, the remaining pilot shall do what?

• A. Notify dispatch and continue manually
• B. Put on and use an approved oxygen mask until the other pilot returns
• C. Descend to a lower altitude immediately
• D. Return to the gate and wait for instructions

Answer: (B)

When flying above 25,000 feet MSL, the air is thin enough that oxygen levels can affect a pilot’s judgment and reaction time. If one pilot leaves the flight station, the remaining pilot must immediately put on and use an approved oxygen mask and continue using it until the other pilot returns. This keeps oxygen levels sufficient to maintain alertness and decision-making, ensuring safe operation of the aircraft while one crew member is absent. The other options don’t address the immediate safety concern of potential hypoxia; while descents or waiting for instructions may be required later, the priority action right away is to ensure proper oxygenation.