Aerial Forum - Altitude Related Hypoxia

During study for the Flight Instructor Rotorcraft Helicopter (FHR) exam, one of the questions posed to the candidates is the following. (Let’s see if you not only get it right, but also understand.)

During a climb to 18,000 feet, the percentage of oxygen in the atmosphere

1. Remains the same

2. Increases

3. Decreases

The Aeronautical Information Manual, paragraph 8-1-2, states that Hypoxia is a state of oxygen deficiency in the body sufficient to impair the functions of the brain and other organs...