What is the first step when an engine fire caution appears in flight?

When an engine fire caution appears in flight, the initial action involves reducing engine power to the minimum acceptable level. This step is crucial because it helps to minimize the risk of further fuel combustion and potential exacerbation of the fire situation. By lowering the power settings, the crew can limit the amount of fuel being supplied to the affected engine, which is a critical measure in controlling the fire.

Additionally, maintaining a lower power setting allows the pilots to manage the aircraft's performance safely while they assess the situation, determine the appropriate emergency procedures to follow, and prepare for a potential diversion or landing. This approach emphasizes safety and control, particularly in a situation where every second counts.

The other actions, such as increasing engine power or shutting off fuel, may enhance the danger by allowing more fuel to reach a fire or jeopardizing the overall control of the aircraft. Utilizing oxygen masks, while important in other emergency scenarios, may not be immediately relevant unless smoke or other indications warrant that measure in the cabin.