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Why must a pilot lean the mixture as the airplane climbs to higher altitude?
Choices
✓ Because the air becomes less dense and the mixture becomes too richcorrect
Thinner air at altitude makes a sea-level mixture too rich, so leaning restores the correct ratio.
Because the air becomes more dense and the mixture becomes too lean
Air density decreases with altitude, making the mixture rich, not lean.
To increase fuel flow and cool the engine
Leaning reduces fuel flow rather than increasing it.
To disable one of the magnetos
Leaning has nothing to do with the ignition system.
Why
As altitude increases the air thins, so a mixture set for sea level becomes too rich; leaning removes excess fuel to restore efficiency and prevent fouling.
FAA source: PHAK Ch. 7browse the reference library →
Original study question written for this course — representative of FAA knowledge-test topics, not an actual current FAA exam question.