The performance, range, and endurance figures listed in the POH are based on a properly leaned engine. The POH can’t tell you how fast, far, or long you’ll fly unless you lean the mixture. Although many pilots think that leaning is only for high altitudes, the truth is that most engines can be safely leaned at any altitude so long as they are operating at less than 75 percent power. (Consult your POH for information on calculating percentage of power.)

Failure to lean is commonly cited as a factor in fuel exhaustion accidents. Learn how to lean your engine, and make leaning a habit on every flight. Some general guidelines are presented below. For specific information, see your airplane’s POH or the engine manufacturer’s operating instructions.

Leaning manually:
On basic airplanes, set cruise power and lean the mixture until the engine runs rough. Then slowly enrich the mixture until the engine runs smoothly. You may see a slight increase in rpm before the engine starts to roughen. If you need to climb to a higher cruising altitude, enrich the mixture before adding power (if you’re at or above 75 percent power) and then lean again when level at your new altitude.

Leaning for take-off:
At high-density-altitude airports, you’ll have to lean before take-off to maximize engine power. Consult your POH for details.

Tip: Two typical mixture settings are “best power” and “best economy.” Best power provides the highest speed for a specific power setting. Best economy trades some of that speed for decreased fuel consumption, and gives the best mileage available at a particular power setting.

Tony BirthComment