Definition
A secondary air intake path that supplies the engine with combustion air when the normal induction air inlet is blocked, typically by induction icing or other obstruction. The alternate source draws unfiltered air from inside the engine compartment, bypassing the air filter and the iced-over inlet so the engine can continue to receive air for combustion.
Plain English
A backup way for the engine to get the air it needs to run, used when the normal air inlet is blocked or iced over. Instead of pulling air in through the usual outside opening, the engine pulls warmer air from inside the engine compartment.
Context Anchor
Seen in engine operation and anti-icing discussions, especially when icing could block the engine’s normal air intake.
Derivation
‘Induction’ comes from the Latin inducere, meaning ‘to lead in’ — here, leading air into the engine. ‘Alternate’ means ‘another option,’ not ‘every other one.’ Together: the other way of leading air into the engine when the main path isn’t working.
Why Pilots Care
Allows continued engine operation and prevents power loss or failure when the normal induction path is blocked by ice or contaminants.
Grounding Statement
If ice closes off the engine’s normal air opening, the alternate induction air source gives the engine a second path for air.
Intuition Check
Do not read “alternate” as something used only for convenience. Here it means a backup air path used when the normal engine air path is restricted or blocked.
Example Sentence 1
When the pilot suspected induction icing was choking the engine, they selected the alternate induction air source to restore airflow.
Example Sentence 2
During the preflight, the instructor demonstrated how the alternate induction air source bypasses the blocked air filter.