FAA Ground School Practice Test

What should a pilot do if they experience roughness in the engine during a run-up at a high elevation airport?

1. Increase the throttle setting

2. Check the results obtained with a leaner setting of the mixture

3. Turn off the carburetor heat

4. Change fuel type

The correct answer is: Check the results obtained with a leaner setting of the mixture

When a pilot experiences roughness in the engine during a run-up at a high-elevation airport, checking the results obtained with a leaner setting of the mixture is an appropriate action. High-altitude environments can reduce the air density, which in turn affects the engine's performance by delivering a less than optimal fuel-to-air ratio. In such cases, enriching the mixture can lead to a richer fuel condition that may not be ideal for the lower oxygen levels present at high elevations. By leaning the mixture, the pilot adjusts the fuel flow to match the reduced air density, ensuring that the engine receives fuel in the correct proportion for efficient combustion. This can often resolve rough running conditions, as it helps the engine achieve a smoother operational state. Other options, such as increasing the throttle setting or turning off the carburetor heat, might not address the fundamental issue related to the mixture at high elevation. Changing the fuel type may be unnecessary unless there is a known issue with the current fuel, which is less likely the cause of rough engine performance during a run-up. Thus, checking the results with a leaner mixture is the most appropriate and effective corrective action in this scenario.