What is the result of using a lean mixture at altitude?

Using a lean mixture at altitude leads to improved performance in several ways. At higher altitudes, the air density decreases, which means there is less oxygen available for combustion in the engine. By leaning the mixture, you are adjusting the fuel-air ratio to ensure that it remains optimal for the conditions. This results in more efficient combustion, allowing the engine to produce the necessary power without excessive fuel consumption.

Leaning the mixture also aids in maximizing the engine's performance by preventing problems such as rough running or stalling that can occur when the mixture is too rich (too much fuel compared to air). As you reduce the amount of fuel in relation to the air, the engine operates more smoothly and can maintain better power and efficiency as altitude increases. This balance is crucial for effective flight operations, especially in a commercial setting where performance and fuel efficiency are critical.