Definition
A device worn over the nose and mouth (or the entire face) that delivers supplemental oxygen from an aircraft oxygen system to the user. Oxygen masks come in several types matched to the system supplying them, including continuous-flow masks for low- to medium-altitude use, diluter-demand and pressure-demand masks for higher altitudes, and quick-donning masks designed to be put on with one hand in five seconds or less.
Plain English
A mask that fits over your face so you can breathe extra oxygen from the aircraft's oxygen system when there isn't enough oxygen in the cabin air.
Context Anchor
Seen in high-altitude flight planning, aircraft oxygen equipment checks, and procedures for using oxygen in flight.
Why Pilots Care
Prevents hypoxia and loss of consciousness during high-altitude flight or cabin depressurization.
Intuition Check
Do not think of an oxygen mask as only an emergency item. In aviation, it can be normal planned equipment for flights where the air is too thin to breathe safely for long.
Example Sentence 1
Before takeoff on the high-altitude leg, the pilot checked that each oxygen mask was connected, flowing, and within easy reach of its seat.
Example Sentence 2
During the emergency procedure the first officer verified the seal on the oxygen mask before descending.