Definition
Additional oxygen delivered to a pilot or passengers through a mask or cannula at higher altitudes, where the reduced atmospheric pressure no longer allows the body to absorb enough oxygen from the surrounding air to maintain normal function.
Plain English
Extra oxygen breathed in from a tank or system in the aircraft, used at high altitudes because the air up there is too thin for your body to get enough oxygen on its own.
Context Anchor
Seen in night flying, high-altitude operations, and discussions of factors that affect vision and pilot performance.
Derivation
Supplemental' comes from the Latin supplementum, meaning 'something added to fill a gap.' Here, the oxygen fills the gap left by thin air at altitude.
Why Pilots Care
Even mild lack of oxygen quickly dulls night vision and slows reaction time before other symptoms are noticed.
Grounding Statement
At night and at altitude, a pilot can begin losing visual sharpness before feeling short of breath.
Intuition Check
Supplemental oxygen does not mean oxygen used only during an emergency. Here it means added oxygen used to prevent reduced vision, alertness, or judgment when normal breathing air is not enough.
Example Sentence 1
Planning a long night cross-country at 10,000 feet, the pilot decided to use supplemental oxygen to keep night vision sharp.
Example Sentence 2
On a night cross-country the crew used supplemental oxygen to maintain clear peripheral vision above eight thousand feet.