AIM Text
- For reasons peculiar to military or naval operations (unusual siting conditions, the pitching and rolling of a naval vessel, etc.) the civil VOR/Distance Measuring Equipment (DME) system of air navigation was considered unsuitable for military or naval use. A new navigational system, TACAN, was therefore developed by the military and naval forces to more readily lend itself to military and naval requirements. As a result, the FAA has integrated TACAN facilities with the civil VOR/DME program. Although the theoretical, or technical principles of operation of TACAN equipment are quite different from those of VOR/DME facilities, the end result, as far as the navigating pilot is concerned, is the same. These integrated facilities are called VORTACs.
- TACAN ground equipment consists of either a fixed or mobile transmitting unit. The airborne unit in conjunction with the ground unit reduces the transmitted signal to a visual presentation of both azimuth and distance information. TACAN is a pulse system and operates in the Ultrahigh Frequency (UHF) band of frequencies. Its use requires TACAN airborne equipment and does not operate through conventional VOR equipment.
Source: FAA Aeronautical Information Manual · current edition · paragraph 1-1-5.
Research Notes
AIM 1-1-5 covers VOR Receiver Check — the operational procedures for verifying VOR equipment accuracy.
Check methods (per § 91.171):
- VOT: Tune to VOT frequency. OBS 0° = FROM indication. OBS 180° = TO indication. Tolerance: ±4°.
- Ground checkpoint: Tune to designated checkpoint frequency. Compare indicated bearing to known bearing. Tolerance: ±4°.
- Airborne checkpoint: Over published airborne checkpoint. Tolerance: ±6°.
- Dual VOR check: Both VORs tuned same station. Bearings must agree within 4°.
- Airborne over landmark: Over identifiable landmark 20+ NM from VOR. Tolerance: ±6°.
Documentation: Record date, place, bearing error, and signature. Required in aircraft logbook or permanent record.