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losing GPS on the critical U.S. infrastructure
(e.g.,NAS) has renewed and refocused attention on
LORAN.
16.1.3LORAN is also supported in the Canadian
airspace system. Currently, LORAN receivers are
only certified for en route navigation.
16.1.4Additional information can be found in the
LORAN−C User Handbook," COMDT PUBP
16562.6, or the website:
http://www.navcen.uscg.gov.
16.2LORAN Chain
16.2.1The locations of the U.S. and Canadian
LORAN transmitters and monitor sites are illustrated
in FIG ENR 4.1−6. 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 ENR 4.1−7.
FIG ENR 4.1−6
U.S. and Canadian LORAN System Architecture
AIP ENR 4.1−15
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG ENR 4.1−7
LORAN Chain Based Coverage
16.2.2The 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 ENR 4.1−8.) The timing of the LORAN system
is tightly controlled and synchronized to Coordinated
Universal Time (UTC). Like the GPS, this is a
Stratum1 timing standard.
16.2.3The 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 ENR 4.1−9)
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
Caribou, Maine; (X) at Nantucket, Massachusetts; (Y) at
Carolina Beach, North Carolina, and (Z) at Dana, Indiana.
In order to keep chain operations precise, monitor
receivers are located at Cape Elizabeth, ME; Sandy Hook,
NJ; Dunbar Forest, MI, and Plumbrook, OH. Monitor
receivers continuously measure various aspects of the
quality (e.g., pulse shape) and accuracy (e.g., timing) of
LORAN signals and report system status to a control
station.
16.2.4The line between the Master and each
secondary station is the baseline" for a pair of
stations. Typical baselines are from 600 to
1000nautical miles in length. The continuation of the
baseline in either direction is a baseline extension."
16.2.5At the LORAN transmitter stations there are
cesium oscillators, transmitter time and control
equipment, a transmitter, primary power (e.g.,commercial
or generator) and auxiliary power equipment
(e.g., uninterruptible power supplies and generators),
and a transmitting antenna (configurations may either
have 1 or 4 towers) with the tower heights ranging
from 700 to 1350 feet tall. Depending on the coverage
area requirements a LORAN station transmits from
400 to 1,600 kilowatts of peak signal power.
16.2.6The USCG operates the LORAN transmitter
stations under a reduced staffing structure that is
made possible by the remote control and monitoring
of the critical station and signal parameters. The
actual control of the transmitting station is
ENR 4.1−16 AIP
15 MAR 07 United States of America
Nineteenth Edition Federal Aviation Administration
accomplished remotely at Coast Guard Navigation
Center (NAVCEN) located in Alexandria, Virginia.
East Coast and Midwest stations are controlled by the
NAVCEN. Stations on the West Coast and in Alaska
are controlled by the NAVCEN Detachment (Det),
located in Petaluma, California. In the event of a
problem at one of these two 24 hour−a−day staffed
sites, monitoring and control of the entire LORAN
system can be done at either location. If both NACEN
and NAVCEN Det are down or if there is an
equipment problem at a specific station, local station
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