FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationHard
A mechanic explains proper mixture leaning procedure to a pilot using the exhaust gas temperature (EGT) gauge for best power cruise operation. Which mixture setting corresponds to best power?
- ALeaned to approximately 50 to 100°F rich of peak EGT
- BSet at full rich regardless of EGT indication
- CLeaned to 100°F lean of peak EGT for maximum economy
- DLeaned exactly to peak EGT indication
Show answer & explanationAnswer & explanation
Correct answer: A. Leaned to approximately 50 to 100°F rich of peak EGT
Best power mixture is typically achieved by leaning to a point slightly rich of peak EGT, commonly about 50 to 100°F rich of peak, which provides maximum power output while maintaining an acceptable margin from peak cylinder temperatures. Leaning to exactly peak or lean of peak favors fuel economy over power, and full rich is used for takeoff/high-power settings, not cruise leaning.
Why the other options are wrong
- B. Full rich is excessively rich for cruise and wastes fuel without power benefit.
- C. Lean of peak favors fuel economy at reduced power, not best power.
- D. Peak EGT itself is generally associated with best economy, not best power.
Mixture Leaning for Best Power
A cruise leaning technique where the mixture is set slightly rich of peak EGT (approximately 50-100°F rich) to achieve maximum power output while maintaining a safety margin from peak cylinder temperatures.
- Best power: ~50-100°F rich of peak EGT
- Best economy: leaned to peak EGT or slightly lean of peak
- Full rich used for takeoff/climb, not cruise leaning
Memory trick: Rich of peak for punch, lean of peak for pennies.