Definition
A short-range radar system installed at or near an airport, used by air traffic control to detect and display the position of aircraft within roughly 60 nautical miles of the airport. It provides azimuth (direction) and range (distance) information, but does not directly measure altitude. ASR is used to sequence and separate arriving and departing traffic in the terminal area and can be used to provide ASR approaches when needed.
Plain English
A radar at the airport that lets controllers see where nearby aircraft are and how far away they are, so they can guide them safely in and out.
Context Anchor
You may see ASR mentioned in air traffic control, radar services near busy airports, and ASR approaches where a controller talks a pilot toward the runway using radar information.
Derivation
‘Surveillance’ comes from the French ‘surveiller’, meaning ‘to watch over’. The name describes the radar’s job: keeping watch over the airspace immediately around an airport.
Why Pilots Care
Controllers use ASR to issue radar vectors and maintain safe separation between aircraft near busy airports.
Intuition Check
ASR is not the airplane’s own radar and it is not mainly a weather display for pilots. It is airport-based radar used by controllers to see aircraft positions near the airport.
Example Sentence 1
Approach control used ASR to sequence the inbound traffic for the ILS at the primary airport.
Example Sentence 2
In marginal weather the tower relied on ASR returns to provide traffic advisories inside the terminal area.