Definition
A secondary source of induction air for a fuel-injected engine, drawn from inside the engine cowling rather than through the normal external air intake. It is used when the primary intake or its filter becomes blocked, typically by impact ice, so the engine can continue to receive air for combustion.
Plain English
A backup air supply for the engine. If the main air inlet gets blocked, the engine can pull warm air from inside the cowling instead, keeping it running.
Context Anchor
You encounter alternate air in engine operation, icing conditions, and checklist steps for loss of engine power caused by a blocked air intake.
Derivation
‘Alternate’ comes from the Latin alternatus, meaning ‘one after the other’ or ‘a second option.’ Here it simply means the backup air path the engine switches to when the primary one is unavailable.
Why Pilots Care
Prevents total engine power loss when the air filter ices over, allowing continued safe flight until the aircraft can exit icing conditions.
Grounding Statement
If the engine’s normal air path is blocked, alternate air gives the engine another path to breathe.
Intuition Check
Alternate air does not mean a different kind of air. It means a backup air path or source for the engine.
Example Sentence 1
When the pilot suspected induction icing, he opened the alternate air control to restore airflow to the engine.
Example Sentence 2
Checklist procedures call for alternate air during flight in visible moisture where induction icing is possible.