What should be done when an aircraft engine is left running on the ground with no person onboard?

When an aircraft engine is left running on the ground without anyone on board, it is crucial to ensure that the aircraft's movement is restricted to prevent any potential hazards. Leaving an aircraft with an operating engine unattended can lead to unintended movement, which could pose significant safety risks to nearby personnel and property.

Restricting the aircraft's movement might involve securing the aircraft with wheel chocks, using ground handling equipment, or employing other safety measures such as a tie-down method. This precaution helps ensure that the aircraft remains stationary and does not roll away or create an unsafe environment.

While other options might seem viable, they either do not fully address the safety concerns inherent in leaving an engine running unattended or suggest inappropriate actions that could lead to hazardous situations.