Supplemental oxygen usage when one pilot in cockpit is required above which altitude?

• A. Above FL250
• B. Above FL100
• C. Above FL350
• D. Below FL180

Answer: (A)

The main idea is that oxygen must be available and used to prevent hypoxia when operating at high altitude, especially if only one pilot is in the cockpit. When one pilot is required to be up front, supplemental oxygen is mandated above about 25,000 feet (Flight Level 250). At that altitude the air is so thin that cognitive and motor functions can deteriorate quickly if oxygen isn’t supplied, so the single pilot must use supplemental oxygen to stay alert and safe until the aircraft descends or another pilot can assist.

Lower altitudes like 10,000 feet or 18,000 feet don’t trigger this single-pilot oxygen requirement, and much higher thresholds (like 35,000 feet) aren’t the rule for this scenario. The key point is the single-pilot cockpit condition plus the 25,000-foot threshold.