Definition
A control on a diluter-demand oxygen regulator that, when set to the automix or 'normal' position, allows the regulator to automatically blend cabin air with oxygen in proportions appropriate to the cabin altitude, delivering progressively more pure oxygen as altitude increases. When moved to the '100 percent oxygen' position, the lever shuts off the cabin-air dilution and the regulator delivers undiluted oxygen on demand.
Plain English
A small lever on the oxygen regulator that lets the system mix the right amount of cabin air with the oxygen based on how high you are flying. Flip it the other way and you get pure oxygen instead of a mix.
Context Anchor
Seen on the oxygen regulator or oxygen control panel when using a diluter-demand oxygen system in higher-altitude aircraft operations.
Derivation
Automix' is short for 'automatic mixing.' The lever automates what would otherwise require the pilot to judge how much oxygen to blend with cabin air at each altitude.
Why Pilots Care
Selecting the correct position conserves the limited oxygen supply at moderate altitudes while ensuring full oxygen concentration when needed for safety.
Intuition Check
Do not read “automix” as meaning the system always gives maximum oxygen. In the automatic setting, it mixes air with oxygen as appropriate; 100 percent oxygen is a separate selection.
Example Sentence 1
Before climbing through 10,000 feet, she checked the regulator and confirmed the automix lever was in the normal position.
Example Sentence 2
Before descending through a layer of smoke, the pilot moved the automix lever to 100 percent to receive undiluted oxygen.