What item must be checked before operating a vehicle on the airfield?

Before operating a vehicle on the airfield, it is critical to ensure that all vehicle lights are functioning properly. This is essential for maintaining safety in a busy airfield environment where visibility can be compromised due to varying weather conditions, low light, or other factors. Working lights communicate the vehicle's presence and intentions to other drivers and personnel, significantly reducing the risk of accidents.

Additionally, proper lighting is a standard requirement for airfield operations to ensure compliance with safety regulations, ultimately contributing to the overall safe movement of both vehicles and aircraft on the airfield. While other options like fuel level, steering alignment, and insurance documentation are important aspects of vehicle maintenance and operation, they do not directly impact immediate safety in the same urgent manner as operational lighting does.