Definition
A fuel/air mixture setting that produces the greatest fuel efficiency for a given power setting, accepting a small reduction in power in exchange for lower fuel consumption per mile or per hour. It is leaner than the best power mixture and is typically used in cruise at or below approximately 75% power.
Plain English
A leaner mixture setting used in cruise that burns less fuel, trading a little speed for better range and longer time aloft.
Context Anchor
Seen in aircraft performance charts, especially cruise charts, when comparing fuel flow at different mixture settings.
Derivation
Best refers to the optimum point; economy comes from Greek 'oikonomia,' meaning household management or thrifty use of resources. Together the term names the mixture setting that uses fuel most thriftily.
Why Pilots Care
Choosing best economy extends range, reduces fuel stops, and lowers operating costs while staying within engine temperature limits.
Intuition Check
Best economy does not mean the aircraft is giving its highest performance. It means the engine is being set for fuel saving, which may be different from the setting used for maximum power.
Example Sentence 1
Once level at cruise altitude and power reduced to 65%, the pilot leaned the mixture to best economy for the long leg home.
Example Sentence 2
With best economy selected, the Cessna 172 showed a predicted endurance of five hours instead of four.