← All explained questions · Supplemental · II — Preflight Procedures
If you suspect carb ice based on RPM drop in cruise, the correct action is to
Choices
slowly reduce throttle to lower power and let ice clear naturally.
Lower throttle worsens icing in some cases.
✓ apply FULL carb heat.correct
expect a small additional RPM drop (warmer, less dense air) plus ROUGH RUNNING as ice melts and is ingested. RPM should recover smoothly as ice clears. Monitor; if no recovery, suspect other causes. Carb heat is FULL ON or FULL OFF — partial heat can keep mixture in the dangerous icing range (cool but moisture present). Apply full carb heat: expect 50-150 RPM additional drop (less dense air = less power), then roughness as ice melts and water/ice ingested, then smooth recovery as ice clears and RPM rises. If no recovery, ice may not be the cause.
apply only partial carb heat to avoid roughness.
Partial carb heat can prolong icing range temperature.
increase throttle to maximum to muscle through.
More throttle doesn't melt ice.
Why
expect a small additional RPM drop (warmer, less dense air) plus ROUGH RUNNING as ice melts and is ingested. RPM should recover smoothly as ice clears. Monitor; if no recovery, suspect other causes. Carb heat is FULL ON or FULL OFF — partial heat can keep mixture in the dangerous icing range (cool but moisture present). Apply full carb heat: expect 50-150 RPM additional drop (less dense air = less power), then roughness as ice melts and water/ice ingested, then smooth recovery as ice clears and RPM rises. If no recovery, ice may not be the cause.
FAA source: FAA-H-8083-25C, PHAK Ch. 7, carburetor heat and carburetor icingbrowse the reference library →
Original study question written for this course — representative of FAA knowledge-test topics, not an actual current FAA exam question.