 Ground-controlled approach

In aviation a ground-controlled approach (GCA), is a type of service provided by air-traffic controllers whereby they guide aircraft to a safe landing, including in adverse weather conditions, based on primary radar images.Most commonly a GCA uses information from either a Precision Approach Radar (PAR, for precision approaches with vertical, glidepath guidance) or an Airport Surveillance Radar (ASR, providing a non-precision Surveillance radar approach with no glidepath guidance).