In aircraft with gaseous oxygen systems, how does oxygen flow change as cabin altitude descends?

In aircraft with gaseous oxygen systems, how does oxygen flow change as cabin altitude descends?

• A. Oxygen flow increases as cabin altitude descends
• B. Oxygen flow decreases as cabin altitude descends and eventually stops at lower safe altitudes, with masks supplying cabin air
• C. Oxygen flow remains constant regardless of altitude
• D. Oxygen flow is not affected by altitude

Answer: (B)

Oxygen flow in gaseous systems is tied to altitude. When the aircraft is at high cabin altitude, the regulator opens more to supply sufficient oxygen because the surrounding air is thin. As you descend and the cabin altitude lowers, the need for supplemental oxygen decreases, so the regulator reduces flow and eventually stops delivering pure oxygen. At those lower safe elevations, the masks can simply pass cabin air instead of oxygen. That’s why the best choice states that flow decreases with descent and stops at lower altitudes, with masks supplying cabin air.

Oxygen flow in gaseous systems is tied to altitude. When the aircraft is at high cabin altitude, the regulator opens more to supply sufficient oxygen because the surrounding air is thin. As you descend and the cabin altitude lowers, the need for supplemental oxygen decreases, so the regulator reduces flow and eventually stops delivering pure oxygen. At those lower safe elevations, the masks can simply pass cabin air instead of oxygen. That’s why the best choice states that flow decreases with descent and stops at lower altitudes, with masks supplying cabin air.