What should be done with the mixture during an engine fire in flight?

During an engine fire in flight, setting the mixture to idle cutoff is critical for several reasons. When the mixture is set to idle cutoff, it effectively stops the flow of fuel to the engine. This action is vital for minimizing the risk of fuel igniting from the fire, thereby helping to prevent further escalation of the situation. Reducing the fuel flow can also help in reducing the fire's intensity, providing the pilot with more time to manage the emergency.

In this scenario, leaving the mixture in the rich position would continue to allow fuel to flow to the engine, which could worsen the fire. Adjusting according to altitude is irrelevant in a fire situation, as the immediate priority is to prevent additional fuel from feeding the flames. Increasing the mixture to full power would similarly contribute to a more severe fire condition due to increased fuel flow. Thus, setting the mixture to idle cutoff is the most effective response for managing an in-flight engine fire.