A pilot may not fly within how many hours after donating blood?

• A. 12 hours
• B. 24 hours
• C. 48 hours
• D. 72 hours

Answer: (B)

When you donate blood, your circulating blood volume and oxygen-carrying capacity drop temporarily. In flight, the cabin is pressurized to a level that still presents less oxygen than at sea level, so the body must work with slightly reduced oxygen delivery. Giving the body a day to stabilize allows plasma volume to rebalance and the immediate effects of donation—like dizziness, fatigue, or lightheadedness—to lessen. This 24-hour window provides a safety margin so you’re less likely to experience symptoms during flight.

Shorter periods might not let your body recover fully from the donation, while a longer wait is more conservative than necessary for most people. So waiting about 24 hours aligns with typical aviation medicine guidance to reduce post-donation risk when flying.