The crew oxygen system will supply 100% oxygen at an altitude of __ regardless of the setting.

• A. 20,000 feet
• B. 25,000 feet
• C. 30,000 feet
• D. 35,000 feet

Answer: (C)

The essential idea is that the crew oxygen system has a safety feature that guarantees pure oxygen delivery when you climb high enough. There’s a regulator setting you can adjust at lower altitudes, but once the aircraft reaches a high altitude threshold, the system automatically provides 100% oxygen to the crew regardless of that setting. That threshold is 30,000 feet, so at 30,000 feet and above, the crew receive 100% O2 to protect against hypoxia even if the control knob isn’t set for it. The other options sit below or at different points and don’t represent that automatic override point, which is why 30,000 feet is the best answer.