Definition
A supplemental oxygen system that delivers oxygen to the user only when they inhale (on demand), and automatically mixes, or dilutes, that oxygen with cabin air in a ratio determined by altitude. As altitude increases, the regulator supplies a higher percentage of oxygen until, at very high altitudes, it delivers 100 percent oxygen.
Plain English
An oxygen system that gives you oxygen only when you breathe in, and automatically blends it with cabin air. The higher you fly, the more oxygen it adds to each breath. Above a certain altitude, it gives you pure oxygen.
Context Anchor
Seen in aircraft oxygen system descriptions, crew oxygen mask operation, and maintenance procedures for oxygen regulators and masks.
Derivation
Diluter comes from the Latin diluere, meaning to wash away or thin out — here it means to thin pure oxygen with cabin air. Demand refers to the system only delivering gas when the user demands it by inhaling, rather than flowing continuously.
Why Pilots Care
It conserves limited oxygen supply while protecting against hypoxia during climbs above 10,000 feet.
Intuition Check
Demand does not mean the pilot has to manually request oxygen each time. Here it means the system senses inhalation and delivers oxygen for that breath.
Example Sentence 1
The aircraft's diluter-demand oxygen system supplied a richer oxygen mixture as the crew climbed through 25,000 feet.
Example Sentence 2
During the preflight, the mechanic verified that the diluter-demand oxygen system delivered proper flow on inhalation.