What must ground control obtain before allowing an aircraft to cross an active runway?

Ground control must obtain approval from local control before allowing an aircraft to cross an active runway. This procedure is crucial for maintaining safety within the airport environment. Local control is responsible for managing the movement of aircraft on the runways and taxiways, ensuring that there are no conflicts with departures or arrivals. Upon receiving approval, ground control can confidently direct the aircraft across the runway, knowing that it is safe to do so.

Each incorrect option relates to distinct roles within air traffic management but does not directly pertain to the specific authorization required for runway crossings. For instance, clearance delivery primarily handles initial flight clearances rather than runway crossing permissions. The tower supervisor oversees operations and may have a broader perspective but does not directly authorize ground control's requests. Notification from approach control is relevant for aircraft in the approach phase but doesn’t provide the necessary clearance for runway crossing. Only local control possesses the specific authority required to mitigate potential hazards associated with active runways.