What is a key requirement during preliminary checks before operating the vehicle?

A key requirement during preliminary checks before operating the vehicle is to ensure that the wheels are properly chocked to prevent rolling. This safety measure is critical, particularly for aerial vehicles and other heavy transport equipment, as it secures the vehicle in place and reduces the risk of accidental movement while personnel are entering, exiting, or performing maintenance. Properly chocking the wheels prevents potential injuries and damages associated with unexpected rolling.

Although checking tire pressure, ensuring the fuel tank is full, and verifying that all lights are functioning are important aspects of vehicle safety and preparedness, the primary focus in this context is the immediate safety measure of securing the vehicle's position before operation. This step ensures a safe working environment for operators and any personnel involved in the vehicle's operation or maintenance.