4/20/23 

AIM 

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. 

b. 

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. 

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6.  VHF Omni

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directional Range/Tactical Air Navigation (VORTAC) 

a. 

A VORTAC is a facility consisting of two components, VOR and TACAN, which provides three individual 

services: VOR azimuth, TACAN azimuth and TACAN distance (DME) at one site. Although consisting of more 

than one component, incorporating more than one operating frequency, and using more than one antenna system, 

a VORTAC is considered to be a unified navigational aid. Both components of a VORTAC are envisioned as 

operating simultaneously and providing the three services at all times. 

b. 

Transmitted signals of VOR and TACAN are each identified by three

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letter code transmission and are 

interlocked so that pilots using VOR azimuth with TACAN distance can be assured that both signals being 

received are definitely from the same ground station. The frequency channels of the VOR and the TACAN at 

each VORTAC facility are “paired” in accordance with a national plan to simplify airborne operation. 

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7.  Distance Measuring Equipment (DME) 

a. 

In the operation of DME, paired pulses at a specific spacing are sent out from the aircraft (this is the 

interrogation) and are received at the ground station. The ground station (transponder) then transmits paired 

pulses back to the aircraft at the same pulse spacing but on a different frequency. The time required for the round 

trip of this signal exchange is measured in the airborne DME unit and is translated into distance (nautical miles) 

from the aircraft to the ground station. 

b. 

Operating on the line

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of

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sight principle, DME furnishes distance information with a very high degree of 

accuracy. Reliable signals may be received at distances up to 199 NM at line

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of

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sight altitude with an accuracy 

of better than 

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 mile or 3 percent of the distance, whichever is greater. Distance information received from DME 

equipment is SLANT RANGE distance and not actual horizontal distance. 

c. 

Operating frequency range of a DME according to ICAO Annex 10 is from 960 MHz to 1215 MHz. Aircraft 

equipped with TACAN equipment will receive distance information from a VORTAC automatically, while 

aircraft equipped with VOR must have a separate DME airborne unit. 

d. 

VOR/DME, VORTAC, Instrument Landing System (ILS)/DME, and localizer (LOC)/DME navigation 

facilities established by the FAA provide course and distance information from collocated components under a 

frequency pairing plan. Aircraft receiving equipment which provides for automatic DME selection assures 

reception of azimuth and distance information from a common source when designated VOR/DME, VORTAC, 

ILS/DME, and LOC/DME are selected. 

e. 

Due to the limited number of available frequencies, assignment of paired frequencies is required for certain 

military noncollocated VOR and TACAN facilities which serve the same area but which may be separated by 

distances up to a few miles. 

f. 

VOR/DME, VORTAC, ILS/DME, and LOC/DME facilities are identified by synchronized identifications 

which are transmitted on a time share basis. The VOR or localizer portion of the facility is identified by a coded 

tone modulated at 1020 Hz or a combination of code and voice. The TACAN or DME is identified by a coded 

tone modulated at 1350 Hz. The DME or TACAN coded identification is transmitted one time for each three or 

Navigation Aids 

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