 The ground-controlled approach is useful when the approaching aircraft is not equipped with sophisticated navigation aids, and may also become a life saver when an aircraft's on-board navigation aids are inoperative, as long as one communication radio works.Sometimes the PAR-based ground-controlled approach is also requested by qualified pilots when they are dealing with an emergency on board to lighten their workload.In the United States, instrument approaches must be monitored by a PAR (if one exists with a coinciding final approach course) during certain condition such as times of darkness or low weather depending upon the controlling agency (USAF, U.S. Army, USN or FAA) or upon pilot request.