A pilot flying at 12,500 feet MSL for more than 30 minutes without supplemental oxygen asks a CFI to explain how a pulse-demand oxygen system differs from a continuous-flow system. Which statement is correct?
- AA pulse-demand system delivers 100% oxygen at all times regardless of cabin altitude, unlike continuous-flow systems
- BA pulse-demand system senses the onset of inhalation and delivers a metered pulse of oxygen only during that portion of the breathing cycle, conserving oxygen supply
- CA pulse-demand system requires a diluter-demand mask and cannot be used with a nasal cannula
- DA pulse-demand system delivers oxygen continuously through a cannula regardless of breathing cycle, wasting less oxygen than continuous-flow only during ground operations
Show answer & explanationAnswer & explanation
Correct answer: B. A pulse-demand system senses the onset of inhalation and delivers a metered pulse of oxygen only during that portion of the breathing cycle, conserving oxygen supply
Pulse-demand oxygen systems use a sensor to detect the start of inhalation and deliver a metered pulse of oxygen only during that portion of the breath, rather than continuously flowing oxygen that is partially wasted during exhalation. This conserves the onboard oxygen supply significantly compared to continuous-flow systems, which run constantly.
Why the other options are wrong
- A. Pulse-demand systems typically deliver oxygen mixed appropriately for altitude via cannula, not pure 100% oxygen at all cabin altitudes.
- C. Pulse-demand systems commonly use a cannula, not necessarily a diluter-demand mask.
- D. This describes continuous-flow operation, not pulse-demand, and the efficiency claim is reversed.
Pulse-Demand Oxygen System
An oxygen delivery system that senses the start of inhalation and delivers a metered oxygen pulse only during that phase of breathing, conserving oxygen compared to continuous-flow systems.
- Triggered by inhalation sensor
- Conserves oxygen supply, extending duration
- Commonly used with nasal cannula for cost/comfort at moderate altitudes
Memory trick: Pulse-demand 'sips' oxygen only when you inhale