Definition
A leaner fuel-to-air mixture setting that produces the lowest fuel consumption for a given cruise power setting, accepting a small reduction in airspeed in exchange for better fuel economy and longer range. It is leaner than the best power mixture and is typically used at cruise power settings of 75 percent or less.
Plain English
A mixture setting that uses less fuel per hour at cruise. The engine runs a little slower and the airplane goes a little slower, but you burn less fuel and can fly farther on the fuel you have.
Context Anchor
Seen in cruise performance charts, especially when choosing power, fuel burn, and range numbers for a planned flight.
Derivation
"Economy" comes from the Greek oikonomia, meaning household management or careful use of resources. In this setting, the pilot is managing fuel carefully to make it last, rather than chasing maximum speed.
Why Pilots Care
Selecting best economy mixture extends range and reduces fuel costs on long flights, but must stay within engine temperature limits to avoid damage.
Intuition Check
Do not read “best economy” as simply “the cheapest way to fly.” Here it means the approved fuel-air setting that gives the charted fuel-saving cruise performance without guessing.
Example Sentence 1
Once established at cruise altitude at 65 percent power, she leaned to best economy mixture for the long leg home.
Example Sentence 2
The performance chart shows that best economy mixture at 55 percent power gives the greatest endurance for the aircraft.