At cabin pressure altitudes within 12,500 to 14,000 feet MSL, supplemental oxygen is required for which portion of a flight time?

• A. For that portion of flight time in excess of 30 minutes
• B. For the entire flight regardless of duration
• C. Only during takeoff and landing
• D. Only if automated oxygen is malfunctioning

Answer: (A)

Oxygen is used to counteract hypoxia as altitude increases. When the cabin pressure altitude sits between 12,500 and 14,000 feet, you don’t have to have supplemental oxygen for the whole flight, but you do need it for the portion of the flight time that you are above that altitude beyond the first 30 minutes. In other words, the first 30 minutes at those altitudes can be flown without oxygen, and after that point, oxygen must be available and used for the remaining time you remain above 12,500 feet.