Under what condition may you cross stop bars?

The condition under which you may cross stop bars is when you have received clearance from Air Traffic Control (ATC) and the lights are unlit. This ensures that you have the necessary permission to proceed safely while also confirming that the situation is clear for you to cross. The stop bars are crucial for maintaining safe operations in areas where vehicles share space with aircraft movements; therefore, proceeding without proper clearance could lead to dangerous situations involving conflicting movements.

Receiving ATC clearance is essential in ensuring compliance with airside safety regulations, as ATC is responsible for managing vehicle and aircraft movements and helps prevent accidents. Unlit stop bars indicate that the airfield is in a state where crossing is permissible, provided that you have ATC authorization. This reinforces the importance of communication with ATC in maintaining safety protocols on the airside.