What device opens to allow induction airflow to continue should the primary induction opening become blocked?

• A. Alternate air
• B. Alternate static source
• C. Alternator/generator
• D. Altimeter

Answer: (A)

The induction system has a backup path called alternate air. If the primary induction opening is blocked by ice, debris, or other obstruction, this door or valve opens to supply air from a separate intake to the engine. This keeps the engine breathing and prevents a complete loss of induction airflow, which could lead to a rough run or power loss. The alternate air source is typically a separate duct or intake in the cowling that bypasses the blocked path, and the option is used to maintain engine operation when the normal air intake can’t be used.

The other items aren’t related to providing air for the engine: an alternate static source feeds the pitot-static system for instruments, the alternator/generator supplies electrical power, and the altimeter uses static pressure to measure altitude.