FAA Commercial Pilot Airplane (CAX)Aircraft SystemsEasy
A fuel-injected engine's induction system includes a door that, when opened, allows warm, unfiltered air to bypass the normal induction air filter. Under what condition would a pilot use this alternate air source?
- AWhen the primary induction air filter becomes blocked by ice or debris
- BWhen leaning the mixture for best economy cruise
- CWhen climbing above the engine's critical altitude
- DWhen the propeller governor loses oil pressure
Show answer & explanationAnswer & explanation
Correct answer: A. When the primary induction air filter becomes blocked by ice or debris
The alternate air source provides an unfiltered air path directly into the induction system, bypassing a blocked or iced primary filter so the engine can continue to receive airflow. It is not related to critical altitude, propeller governing, or leaning technique.
Why the other options are wrong
- B. Leaning is a mixture control function, not an induction air function.
- C. Critical altitude relates to turbocharging, not induction air filtering.
- D. Propeller governor oil pressure is unrelated to induction air source.
Alternate Induction Air Source
A door or valve that allows unfiltered, often warmer, air to enter the induction system if the normal filtered air path becomes blocked.
- Bypasses a blocked or iced primary air filter
- Air is typically warmer and unfiltered
- Common on both fuel-injected and carbureted high-performance engines
Memory trick: Blocked filter? Open the alternate door for backup breath.