Definition
ASR/PAR are two types of radar approaches in which an air traffic controller provides verbal guidance to a pilot to align with and descend to a runway. An ASR (Airport Surveillance Radar) approach gives the pilot heading instructions to keep the aircraft on the final approach course, along with recommended altitudes at each mile from the runway, but provides no glidepath guidance. A PAR (Precision Approach Radar) approach gives both course (azimuth) and glidepath guidance, with the controller continuously telling the pilot whether they are on, above, or below the glidepath and on, left, or right of course.
Plain English
Two kinds of radar-guided approaches where a controller talks the pilot down to the runway. ASR is the basic version -- the controller tells you which way to turn but not how to descend. PAR is the precise version -- the controller tells you both which way to turn and how to manage your descent, all the way to the runway.
Context Anchor
Seen in instrument approach discussions, including timed approaches from a holding fix, when radar approaches are included with other possible approach types.
Derivation
ASR stands for Airport Surveillance Radar -- 'surveillance' meaning the radar that watches general traffic around the airport. PAR stands for Precision Approach Radar -- 'precision' because it gives the precise vertical guidance that ASR lacks.
Why Pilots Care
Allows a safe arrival at airports without other instrument landing systems when weather is low.
Intuition Check
ASR/PAR does not mean one combined approach. It means the approach may involve either Airport Surveillance Radar or Precision Approach Radar, depending on the procedure and radar service being used.
Example Sentence 1
After losing the GPS, the pilot requested an ASR approach and followed the controller's heading instructions while descending to each published step-down altitude.
Example Sentence 2
On the PAR approach the controller kept giving heading and glidepath corrections until touchdown.