Which term describes an oxygen system that maintains constant oxygen partial pressure by mixing with air as altitude changes?

• A. Differential ailerons
• B. DGPS
• C. Diluter-demand oxygen system
• D. Direct indication

Answer: (C)

Maintaining the same oxygen partial pressure as you climb requires adjusting the mix of oxygen with ambient air. A diluter-demand oxygen system does exactly that: it blends oxygen with surrounding air in variable proportions as altitude changes so the inspired gas keeps a relatively constant partial pressure of oxygen. It also delivers oxygen on demand, meaning oxygen is supplied when you inhale, and the regulator automatically increases the dilution with air as you ascend to keep the PO2 within safe levels. The other terms don’t describe this mixing function—differential ailerons are flight controls, DGPS is navigation, and direct indication refers to a type of indication but not the balancing of O2 with altitude.