ATPL Human Factors Test 2026 – 400 Free Practice Questions to Pass the Exam

The requirement for a continuous oxygen supply for passengers comes into play particularly at higher altitudes due to the decrease in atmospheric pressure and the corresponding drop in available oxygen. Above FL150 (15,000 feet), the oxygen levels in the atmosphere can become insufficient for normal physiological function, especially during prolonged exposure. This is why regulations mandate that aircraft provide a continuous supply of supplemental oxygen to passengers and crew above this altitude. Prolonged exposure to altitudes above FL150 without supplemental oxygen can lead to hypoxia, which is a condition characterized by insufficient oxygen reaching the body's tissues.

At altitudes above FL250, not only is additional oxygen required for passengers, but there are also specific regulations regarding the need for oxygen to be available for crew members and potential use in emergency situations. However, the critical threshold for continuous oxygen supply to passengers is established at FL150, making this the correct answer.