AIM Text
- PAR is designed for use as a landing aid rather than an aid for sequencing and spacing aircraft. PAR equipment may be used as a primary landing aid (See Chapter 5, Air Traffic Procedures, for additional information), or it may be used to monitor other types of approaches. It is designed to display range, azimuth, and elevation information.
- 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 degrees, and elevation to 7 degrees, only the final approach area is covered. Each scope is divided into two parts. The upper half presents altitude and distance information, and the lower half presents azimuth and distance.
Source: FAA Aeronautical Information Manual · current edition · paragraph 4-5-4.
Research Notes
AIM 4-5-4 covers Air Traffic Control Radar Beacon System (ATCRBS) — the secondary surveillance radar system that uses transponder interrogations.
Mode A: Returns the 4-digit code set by the pilot. Used for identification. Common discrete codes are issued by ATC. Standard non-discrete codes:
- 1200 — VFR (default)
- 7500 — hijack
- 7600 — radio communications failure
- 7700 — emergency
Mode C: Returns altitude. Required in many airspace per § 91.215. Calibrated to read altitude on 29.92 setting regardless of pilot's altimeter.
Mode S: Returns additional aircraft-specific data (aircraft ID, intentions, etc.). Foundation for TCAS and ADS-B operations.
The 'ident' function: A button on the transponder that triggers a special radar return identifying the aircraft. ATC uses "squawk and ident" to confirm aircraft identity. Only press IDENT when specifically requested.
Reference: § 91.215; AIM 4-1-20 (Transponder Operation); AIM 4-5-4.