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of the aircraft, time of the observation, type of
aircraft and describe the condition observed; the type
of receivers in use is also useful information. Reports
can be made in any of the following ways:
1. Immediate report by direct radio communication
to the controlling Air Route Traffic Control
Center (ARTCC), Control Tower, or FSS. This
method provides the quickest result.
2. By telephone to the nearest FAA facility.
3. By FAA Form 8000−7, Safety Improvement
Report, a postage−paid card designed for this
purpose. These cards may be obtained at FAA FSSs,
Flight Standards District Offices, and General
Aviation Fixed Base Operations.
c. In aircraft that have more than one receiver,
there are many combinations of possible interference
between units. This can cause either erroneous
navigation indications or, complete or partial
blanking out of the communications. Pilots should be
familiar enough with the radio installation of the
particular airplanes they fly to recognize this type of
interference.
1−1−15. LORAN
a. Introduction
1. The LOng RAnge Navigation−C (LORAN)
system is a hyperbolic, terrestrial−based navigation
system operating in the 90−110 kHz frequency band.
LORAN, operated by the U.S. Coast Guard (USCG),
has been in service for over 50 years and is used for
navigation by the various transportation modes, as
well as, for precise time and frequency applications.
The system is configured to provide reliable, all
weather navigation for marine users along the U.S.
coasts and in the Great Lakes.
2. In the 1980’s, responding to aviation user and
industry requests, the USCG and FAA expanded
LORAN coverage to include the entire continental
U.S. This work was completed in late 1990, but the
LORAN system failed to gain significant user
acceptance and primarily due to transmitter and user
equipment performance limitations, attempts to
obtain FAA certification of nonprecision approach
capable receivers were unsuccessful. More recently,
concern regarding the vulnerability of Global
Positioning System (GPS) and the consequences of
losing GPS on the critical U.S. infrastructure (e.g.,
NAS) has renewed and refocused attention on
LORAN.
2/19/04 AIM
Air Navigation Aids 1−1−17
3. LORAN is also supported in the Canadian
airspace system. Currently, LORAN receivers are
only certified for en route navigation.
4. Additional information can be found in the
“LORAN−C User Handbook,” COMDT PUB−
P16562.6, or the website www.navcen.uscg. gov.
b. LORAN Chain
1. The locations of the U.S. and Canadian
LORAN transmitters and monitor sites are illustrated
in FIG 1−1−11. Station operations are organized into
subgroups of four to six stations called “chains.” One
station in the chain is designated the “Master” and the
others are “secondary” stations. The resulting chain
based coverage is seen in FIG 1−1−12.
FIG 1−1−11
U.S. and Canadian LORAN System Architecture
FIG 1−1−12
LORAN Chain Based Coverage
AIM 2/19/04
1−1−18 Air Navigation Aids
2. The LORAN navigation signal is a carefully
structured sequence of brief radio frequency pulses
centered at 100 kHz. The sequence of signal
transmissions consists of a pulse group from the
Master (M) station followed at precise time intervals
by groups from the secondary stations, which are
designated by the U.S. Coast Guard with the letters V,
W, X, Y and Z. All secondary stations radiate pulses
in groups of eight, but for identification the Master
signal has an additional ninth pulse. (See
FIG 1−1−13.) The timing of the LORAN system is
tightly controlled and synchronized to Coordinated
Universal Time (UTC). Like the GPS, this is a
Stratum 1 timing standard.
3. The time interval between the reoccurrence
of the Master pulse group is called the Group
Repetition Interval (GRI). The GRI is the same for all
stations in a chain and each LORAN chain has a
unique GRI. Since all stations in a particular chain
operate on the same radio frequency, the GRI is the
key by which a LORAN receiver can identify and
isolate signal groups from a specific chain.
EXAMPLE−
Transmitters in the Northeast U.S. chain (FIG 1−1−14)
operate with a GRI of 99,600 microseconds which is
shortened to 9960 for convenience. The master station (M)
at Seneca, New York, controls secondary stations (W) at
　
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