 Military organizations and NATO refer to the former as "medical evacuation (MEDEVAC)" and to the latter as "casualty evacuation (CASEVAC)".Air Traffic Control (ATC) grants special treatment to air ambulance operations, much like a ground ambulance using lights and a siren, only when they are actively operating with a patient.When this happens, air ambulance aircraft take the call sign MEDEVAC (formerly LIFEGUARD) and receive priority handling in the air and on the ground.