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making these VOR receiver checks.
4.5.2Locations of airborne check points, ground
check points, and VOTs are published in the A/FD
and are depicted on the A/G voice communication
panels on the FAA IFR area chart and IFR en route
low altitude chart.
4.5.3If a dual system VOR (units independent of
each other except for the antenna) is installed in the
aircraft, one system may be checked against the other.
Turn both systems to the same VOR ground facility
and note the indicated bearing to that station. The
maximum permissible variations between the two
indicated bearings is 4 degrees.
5. Distance Measuring Equipment (DME)
5.1In 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 (NM)) from the aircraft
to the ground station.
5.2Operating 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% of the
distance, whichever is greater. Distance information
received from DME equipment is SLANT RANGE
distance and not actual horizontal distance.
5.3Operating 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.
5.4VOR/DME, VORTAC, ILS/DME, and
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 whenever designated VOR/DME, VORTAC,
ILS/DME, and LOC/DME are selected.
5.5Due 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.
5.6VOR/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
by a combination of code and voice. The TACAN or
DME is identified by a coded tone modulated at
1350Hz. The DME or TACAN coded identification
is transmitted one time for each three or four times
that the VOR or localizer coded identification is
transmitted. When either the VOR or the DME is
inoperative, it is important to recognize which
identifier is retained for the operative facility. A
signal coded identification with a repetition interval
of approximately 30 seconds indicates that the DME
is operative.
5.7Aircraft equipment which provides for
automatic DME selection assures reception of
azimuth and distance information from a common
source whenever designated VOR/DME, VORTAC,
and ILS/DME navigation facilities are selected.
Pilots are cautioned to disregard any distance
displays from automatically selected DME
equipment when VOR or ILS facilities, which do not
have the DME feature installed, are being used for
position determination.
ENR 4.1−4 AIP
15 MAR 07 United States of America
Nineteenth Edition Federal Aviation Administration
6. Tactical Air Navigation (TACAN)
6.1For reasons peculiar to military or naval operations
(unusual siting conditions, the pitching and
rolling of a naval vessel, etc.) the civil VOR/DME
system of air navigation was considered unsuitable
for military or naval use. A new navigational system,
Tactical Air Navigation (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
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