Aeronautical Information Manual (AIM), page 58

Index   57 -- Page 58 -- 59


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

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
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 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
single coded identification with a repetition interval
of approximately 30 seconds indicates that the DME
is operative.

g. Aircraft equipment which provides for auto-
matic DME selection assures reception of azimuth
and distance information from a common source
when 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.

1-1-8. Navigational Aid (NAVAID) Service

a. Most air navigation radio aids which provide
positive course guidance have a designated standard
service volume (SSV). The SSV defines the reception
limits of unrestricted NAVAIDs which are usable for
random/unpublished route navigation.

b. A NAVAID will be classified as restricted if it
does not conform to flight inspection signal strength
and course quality standards throughout the
published SSV. However, the NAVAID should not be
considered usable at altitudes below that which could
be flown while operating under random route IFR
conditions (14 CFR Section 91.177), even though
these altitudes may lie within the designated SSV.
Service volume restrictions are first published in
Notices to Airmen (NOTAMs) and then with the
alphabetical listing of the NAVAIDs in the Chart
Supplement U.S.
c. Standard Service Volume limitations do not
apply to published IFR routes or procedures.
d. VOR/DME/TACAN Standard Service Vol-
umes (SSV).

1. Standard service volumes (SSVs) are graph-
ically shown in FIG 1-1-1, FIG 1-1-2, FIG 1-1-3,
FIG 1-1-4, and FIG 1-1-5. The SSV of a station is
indicated by using the class designator as a prefix to
the station type designation.

1-1-4 Navigation Aids

Page 58 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   57 -- Page 58 -- 59