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.
1-1-6. VHF Omni-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-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.
1-1-7. 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-of-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-of-sight altitude with an accuracy
of better than 1/2 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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