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navigation, then an alarm will be activated to alert the
pilot.
16.3.6LORAN signals operate in the low frequency
band (90−110 kHz) that has been reserved for marine
navigation signals. Adjacent to the band, however,
are numerous low frequency communications
transmitters. Nearby signals can distort the LORAN
signals and must be eliminated by the receiver to
assure proper operation. To eliminate interfering
signals, LORAN receivers have selective internal
filters. These filters, commonly known as notch
filters," reduce the effect of interfering signals.
16.3.7Careful installation of antennas, good metal−
to−metal electrical bonding, and provisions for
precipitation noise discharge on the aircraft are
essential for the successful operation of LORAN
receivers. A LORAN antenna should be installed on
an aircraft in accordance with the manufacturer’s
instructions. Corroded bonding straps should be
replaced, and static discharge devices installed at
points indicated by the aircraft manufacturer.
16.4LORAN Navigation
16.4.1An airborne LORAN receiver has four major
parts:
16.4.1.1Signal processor;
16.4.1.2Navigation computer;
16.4.1.3Control/display, and
16.4.1.4Antenna.
16.4.2The signal processor acquires LORAN
signals and measures the difference between the
time−of−arrival of each secondary station pulse
group and the Master station pulse group. The
measured TDs depend on the location of the receiver
in relation to the three or more transmitters.
AIP ENR 4.1−21
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG ENR 4.1−11
First Line−of−Position
16.4.2.1The first TD will locate an aircraft
somewhere on a line−of−position (LOP) on which the
receiver will measure the same TD value.
16.4.2.2A second LOP is defined by a TD
measurement between the Master station signal and
the signal form another secondary station.
FIG ENR 4.1−12
Second Line−of−Position
16.4.2.3The intersection of the measured LOPs is
the position of the aircraft.
FIG ENR 4.1−13
Intersection of Lines−of−Position
16.4.3The navigation computer converts TD values
to corresponding latitude and longitude. Once the
time and position of the aircraft are established at
twopoints, distance to destination, cross track error,
ground speed, estimated time of arrival, etc., can be
determined. Cross track error can be displayed as the
vertical needle of a course deviation indicator, or
digitally, as decimal parts of a mile left or right of
course.
16.5Notices to Airmen (NOTAMs) are issued for
LORAN chain or station outages. Domestic
NOTAM(D)s are issued under the identifier LRN."
International NOTAMs are issued under the KNMH
series. Pilots may obtain these NOTAMs from FSS
briefers upon request.
16.6LORAN Status Information.To find out
more information on the LORAN system and its
operational status you can visit the website
http://www.navcen.uscg.gov/loran/default.htm or
contact NAVCEN’s Navigation Information Service
(NIS) watchstander, phone(703) 313−5900,
fax(703) 313−5920.
16.7LORAN’s future.The U.S. will continue to
operate the LORAN system in the short term. During
this time, the FAA LORAN evaluation program,
ENR 4.1−22 AIP
15 MAR 07 United States of America
Nineteenth Edition Federal Aviation Administration
being conducted with the support of a team
comprising government, academia, and industry, will
identify and assess LORAN’s potential contributions
to required navigation services for the National
Airspace System (NAS), and support decisions
regarding continued operation of the system. If the
government concludes LORAN should not be kept as
part of the mix of federally provided radio navigation
systems, it will give the users of LORAN reasonable
notice so that they will have the opportunity to
transition to alternative navigation aids.
17. Inertial Reference Unit (IRU), Inertial
Navigation System (INS), and Attitude
Heading Reference System (AHRS)
17.1IRUs are self−contained systems comprised of
gyros and accelerometers that provide aircraft
attitude (pitch, roll, and heading), position, and
velocity information in response to signals resulting
from inertial effects on system components. Once
aligned with a known position, IRUs continuously
calculate position and velocity. IRU position
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