Airport Surveillance Radar and Precision Approach Radar IAPs
Congrats! You just found the simplest approach plate known to man! The Radar Minimums!
This is what an approach plate looks like for an ASR or PAR approach. You just read the minimums, ATC takes care of the rest….no frequencies to set for a LOC or GPS!.
When you want to fly, for example, the ASR approach in KNQX for runway 14, you will simply look at ASR, go down to runway 14 and read across that, for categories A and B aircraft, the minima are 420′ msl and 1sm visibility. There is also note 10 that applies, so let’s look lower at note 10 and see what we should be aware of. Note 10 says, when the VGSI (papi or vasi) is not working, you cannot fly that procedure at night.
The end! For more information to better understand read below the plate. Note: everything here is “non-precision” with the exception of true PAR (that is PAR with a Glideslope). PAR is a precision approach.
ASR is designed to provide relatively short-range coverage in the general vicinity of an airport and to serve as an expeditious means of handling terminal area traffic through observation of precise aircraft locations on a radarscope. Nonprecision instrument approaches are available at airports that have an approved surveillance radar approach procedure. ASR provides radar vectors to the final approach course and then azimuth information to the pilot during the approach. In addition to the range (distance) from the runway, the pilot is advised of MDA, when to begin the descent, and when the aircraft is at the MDA. If requested, recommended altitudes are furnished each mile while on final.
PAR is designed to be used as a landing aid displaying range, azimuth, and elevation information rather than as an aid for sequencing and spacing aircraft. PAR equipment may be used as a primary landing aid, or it may be used to monitor other types of approaches. Two antennas are used in the PAR array: one scanning a vertical plane and the other scanning horizontally. Since the range is limited to 10 miles, azimuth to 20°, and elevation to 7°, only the final approach area is covered. The controller’s scope is divided into two parts. The upper half presents altitude and distance information, and the lower half presents azimuth and distance.
PAR is a system in which a controller provides highly accurate navigational guidance in azimuth and elevation to a pilot. Pilots are given headings to fly to direct them to and keep their aircraft aligned with the extended centerline of the landing runway. They are told to anticipate glide path interception approximately 10–30 seconds before it occurs and when to start the descent. The published decision height (DH) is given only if the pilot requests it. If the aircraft is observed to deviate above or below the glide path, the pilot is given the relative amount of deviation by use of terms “slightly” or “well” and is expected to adjust the aircraft’s rate of descent/ ascent to return to the glide path. Trend information is also issued with respect to the elevation of the aircraft and may be modified by the terms “rapidly” and “slowly” (e.g., “well above glide path, coming down rapidly”).
Range from touchdown is given at least once each mile. If an aircraft is observed by the controller to proceed outside of specified safety zone limits in azimuth and/or elevation and continues to operate outside these prescribed limits, the pilot will be directed to execute a missed approach or to fly a specified course unless the pilot has the runway environment (runway, approach lights, etc.) in sight. Navigational guidance in azimuth and elevation is provided to the pilot until the aircraft reaches the published decision altitude (DA)/ DH. Advisory course and glide path information is furnished by the controller until the aircraft passes over the landing threshold, at which point the pilot is advised of any deviation from the runway centerline. Radar service is automatically terminated upon completion of the approach.
When this is useful…
Well if every navigational instrument in your aircraft failed, and descending to the controller’s MVA (minimum vectoring altitude) still had you in the clouds, you could shoot an approach using nothing but your airplane and a cell phone or handheld radio in theory. It’s good to practice these from time to time, and you will find that ASR approaches can be found at many Class C airports, while PAR approaches are generally found only at military airports. You know if there is an ASR or PAR approach offered for an airport by the plate titles “radar minimums” being published along with the rest of the approach plates for that airport (check near the rest of the approach plates for that airport (on your app) or in the appendix of your approach chart booklet).
The other more practical time this is useful is when you are flying partial panel or for any other reason you might need ATC to keep a closer eye on you. Any airport capable of ASR/PAR approaches has precision approach RADAR and the approach controller can offer you very detailed information about your heading and course, which can be great when nearly 100% of your focus is just keeping the airplane right side up and you can use them to tell you when to start and stop a turn, rather than being distracted having to scan a compass that is bobbling around in the turbulence.