Tactical Air Navigation


  • Tactical Air Navigation (TACAN) was developed to provide precise geographical fixing of the aircraft's position for the military where the Distance Measuring Equipment (DME) system is deemed unsuitable
  • Like a VOR, provides 360 radials coming from the station
  • VOR and TACAN systems collocated are called VORTACs
  • An additional advantage is that TACAN ground equipment is compact and relatively easy to transport
  • IDs every 35 seconds
  • The OFF position will disconnect the unit from the aircraft power supply
  • STBY will receive magnetic bearing information only from ground TACAN navigation facilities
  • In the T/R position, the TACAN receives magnetic bearing and distance information
  • Cannot be used to transmit and receive voice
  • Will identify itself with a Morse code identifier about every 37.5/32 seconds
  • Transmitted one time for each 3 or 4 times that a VOR signal is transmitted when identifying a VORTAC


  • 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


  1. DME decreases to minimum
  2. Needle rotates 180°
  3. CDI oscillates from side to side
  4. TO/FORM indicator switches from TO to FROM

Instrument indications will fluctuate when close to the station; this does not necessarily mean your aircraft is off course. Do not chase the needle when close to the station. Limit heading corrections for drift when close to avoid overshooting


  • TACAN operates in the UHF (1000 MHz) band with 126 two-way channels in the operational mode (X or Y) for 252 total
  • Air-to-ground DME frequencies are in the 1025 to 1150 MHz range
  • Ground-to-air frequencies are in the 962 to 1213 MHz range

Ground Equipment:

  • Consists of a rotating type antenna transmitting bearing and a receiver-transmitter (transponder) for transmitting distance information
  • Ground stations are usually dual transmitter equipped
  • One operational and the other standby
  • Sometimes TACAN reception might be suspected of being in error or bearing/distance unlock conditions may be encountered in flight

Distance Measuring Equipment (DME):

  • The aircraft sends an interrogation to the ground station and the station sends a reply back
  • The elapsed time between transmission and reception is the distance in NM
  • The pulses require about 12 microseconds round trip travel time per NM of distance
  • Replies are random to ensure other aircraft using the same station get a unique signal
  • If the signals are interrupted, a memory circuit maintains the last distance indication for 10 seconds
  • After 10 seconds, a search function begins to lock back onto the station, taking up to 22 seconds
  • Furnishes reliable, line of sight, slant range information at distances up to 199 NM with an accuracy of 2 mile or 3% of the distance, whichever is greater


  • Cannot transmit voice
  • DME equipment is an integral part in providing slant range up to 399.9 NM with an accuracy of 2 miles or 3% of the distance, whichever is greater
  • Cone of confusion:
    • Exists where TACAN azimuth information is not available
    • The "cone" varies from 60° to 110° wide
    • TACAN DME and ID signal will be received and station passage will be noted by minimum DME
    • Although narrow at low altitudes, this "cone" expands to about 18 NM across at 30,000'
    • Because of the size of TACAN cone of confusion, holding on a TACAN will always be established using DME
  • Standard Service Volume applies (T, L, H stations):
    • SSV defines the interference free reception limits of unrestricted NAVAIDs, which are usable for random/unpublished route navigation
    • Reception may be possible beyond the ranges, however interference from other stations on the same frequencies may cause 40° off bearing lock-on
  • 40° off bearing TACAN pointer lock-on error:
    • Locking on to multiples of 40° from the desired radial due to inherent operating functions of the older crystal controlled receivers
    • Solid-state electronics in the T-45C should preclude this problem from occurring
    • Re-channeling the receiver and tuning back to the original station may remedy the error
  • Failure to lock on:
    • Misalignment of equipment
    • Worn aircraft control box
    • Re-channeling the receiver and tuning from the opposite direction back to the original station may remedy the error
  • Co-channel interference:
    • Receiving signals (DME, azimuth, identifier) from more than one TACAN station due to the relationship between aircraft's high altitude and station locations


  • Pilots should be aware of the possibility of momentary erroneous indications on cockpit displays when the primary signal generator for a ground-based navigational transmitter is inoperative
    • Pilots should disregard any navigation indication, regardless of its apparent validity, if the particular transmitter was identified by NOTAM or otherwise as unusable or inoperative