How does a pilot control the air/fuel ratio in an aircraft?

Controlling the air/fuel ratio is critical for optimal engine performance, fuel efficiency, and engine health. The correct answer, through the mixture control, directly affects the proportion of air to fuel that enters the engine. When a pilot adjusts the mixture control, they can enrich or lean the fuel mixture, providing the right balance based on altitude and performance needs.

At higher altitudes, the air density decreases, which means there's less oxygen available for combustion. To maintain an efficient combustion process and prevent engine damage or inefficiency, the pilot needs to lean out the mixture. Conversely, at lower altitudes or during specific performance phases like takeoff, enriching the mixture can enhance power output.

The other methods listed do not directly alter the air/fuel ratio. For instance, adjusting the throttle controls the power output and airflow through the engine but does not change the mixture of fuel and air. The fuel pump is responsible for delivering fuel under pressure to the engine, but it does not influence the mixture directly. Similarly, modifying propeller pitch affects the propulsion efficiency and thrust but does not alter the air/fuel mixture entering the combustion chamber.