What is "ground-controlled approach"

n. aircraft landing in bad weather in which the pilot is talked down by ground control using precision approach radar [syn: GCA]

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. 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.