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). The term GCA may refer to any type of ground radar guided approach such as a PAR, PAR without glideslope or ASR. An approach using ASR is known as a surveillance approach. When both vertical and horizontal guidance from the PAR is given, the approach is termed a precision approach. If no PAR glidepath is given, even if PAR equipment is used for lateral guidance, it is considered a non-precision approach.