Precision approach radar or PAR is a type of radar guidance system designed to provide lateral and vertical guidance to an aircraft pilot for landing, until the landing threshold is reached.[1] Controllers monitoring the PAR displays observe each aircraft's position and issue instructions to the pilot that keep the aircraft on course and glidepath during final approach. After the aircraft reaches the decision height (DH) or decision altitude (DA), further guidance is advisory only. The overall concept is known as ground-controlled approach (GCA), and this name was also used to refer to the radar systems in the early days of its development.
PAR radars use a unique type of radar display with two separate "traces", separated vertically. The upper trace shows the elevation of a selected aircraft compared to a line displaying the ideal glideslope, while the lower shows the aircraft's horizontal position relative to the runway midline. GCA approaches normally start with the controller relaying instructions to bring the aircraft into the glidepath and then begin any corrections needed to bring it onto the centerline.
Precision approach radars are most frequently used at military air traffic control facilities. Many of these facilities use the AN/FPN-63, AN/MPN, or AN/TPN-22. These radars can provide precision guidance from a distance of 10 to 20 miles down to the runway threshold. PAR is mostly used by the Navy, as it does not broadcast directional signals which might be used by an enemy to locate an aircraft carrier.
- ^ Wragg, David W. (1973). A Dictionary of Aviation (first ed.). Osprey. p. 215. ISBN 9780850451634.