What type of clearance must be obtained before entering an active runway?

Answer: C — Air Traffic Control (ATC) clearance

To enter an active runway, one must obtain Air Traffic Control (ATC) clearance. This requirement is critical for maintaining safety and order at the airfield, as active runways are the locations where aircraft take off and land, making them especially busy and potentially hazardous areas. ATC clearance ensures that the air traffic controllers are aware of all movements on and around the runway, allowing them to manage aircraft operations effectively. This includes coordinating the timing of arrivals and departures, ensuring that there are no conflicts between aircraft and vehicles on the runway, and providing necessary guidance to drivers, particularly those unfamiliar with the airfield layout. While flight clearance pertains to authorizing aircraft operations in the sky and ground clearance refers to movements on taxiways and other non-active areas, it is the ATC clearance specifically that addresses the critical nature of active runways. Emergency clearance is not a standard procedure for entering active runways but rather a response to unexpected situations requiring immediate action.