If only one pilot is on the flight deck above 25,000 feet, that pilot must use oxygen.

• A. The sole pilot on deck above 25k must use oxygen
• B. Both pilots must use oxygen
• C. Oxygen is optional
• D. No oxygen required

Answer: (A)

High altitude means thinner air and less oxygen reaching the bloodstream, which can cause hypoxia quickly. The safety rule for flight crews is that, once the flight deck is above 25,000 feet, the pilot on duty must be using supplemental oxygen. When there’s only one pilot on the flight deck at that altitude, that pilot must wear or use oxygen to maintain mental clarity and physical performance, since there isn’t another crewmember to notice and respond to any signs of hypoxia. So the correct answer reflects this single-pilot requirement above 25,000 feet.