If an engine starts on the ground and catches fire, what should you do next?

In the scenario where an engine starts on the ground and catches fire, the safest and most effective immediate action is a combination of shutting down the engine and turning off the fuel and ignition systems. By shutting down the engine, you minimize the risk of further fuel flow and additional power output, which could exacerbate the fire. Turning off the fuel and ignition is crucial as it prevents any additional fuel from feeding the fire and eliminates the source of ignition.

This response addresses the critical need to extinguish the fire and prevent it from spreading or worsening. The collaborative action of shutting down the engine while simultaneously cutting off fuel and ignition ensures a prompt response that can mitigate damage and enhance safety for the occupants. Though increasing power to higher RPM could momentarily give a more dramatic engine sound, it would only serve to exacerbate the combustion scenario rather than effectively address the fire.

Hence, the answer includes both the necessity of engine shutdown and the deactivation of the fuel and ignition systems as essential actions to take when faced with an engine fire during ground operations.