Surveillance radar approach

A Surveillance Radar Approach (SRA or ASR) is an aviation term for a type of instrument approach provided with active assistance from Air Traffic Control during the final approach phase. It requires no special equipment in addition to a standard surveillance radar system used by Air Traffic Control (ATC). It thus differs from most other instrument approaches which utilise a radio navigation system to provide guidance during the final approach.

As it requires no special equipment to be carried on board an aircraft, an SRA is considered a fall-back approach for aircraft that are having instrument or electrical problems and therefore cannot rely on on-board instruments; it is also sometimes provided to runways that do not usually receive instrument traffic and therefore do not have any other approach aids provided.

During the approach, the controller provides headings to keep the aircraft on the runway centreline as viewed on radar. The controller also reads out advisory altitudes based upon the observed range from touchdown: pilots can use these to assist with their descent planning. Since guidance is only provided in azimuth, SRAs are non-precision approaches. Controller guidance terminates at between 2 nmi and 0.5 nmi from touchdown, at which point the pilot must either be visual with the runway, or must go around.