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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.
7. Careful installation of antennas, good metalto-
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.
d. LORAN Navigation
1. An airborne LORAN receiver has four major
parts:
(a) Signal processor;
(b) Navigation computer;
(c) Control/display, and
(d) Antenna.
2. The 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.
2/14/08 AIM
Navigation Aids 1-1-23
FIG 1-1-16
First Line-of-Position
(a) The first TD will locate an aircraft
somewhere on a line-of-position (LOP) on which the
receiver will measure the same TD value.
(b) A second LOP is defined by a TD
measurement between the Master station signal and
the signal from another secondary station.
FIG 1-1-17
Second Line-of-Position
(c) The intersection of the measured LOPs is
the position of the aircraft.
FIG 1-1-18
Intersection of Lines-of-Position
3. The 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.
e. Notices 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.
f. LORAN status information. To find
outmoreinformation on the LORAN system
anditsoperational status you can visit
http://www.navcen.uscg.gov/loran/default.htm
orcontact NAVCEN's Navigation Information
Service (NIS) watchstander, phone(703) 313-5900,
fax (703) 313-5920.
g. LORAN's future. The U.S. will continue to
operate the LORAN system in the short term. During
this time, the FAA LORAN evaluation program,
being conducted with the support of a team
AIM 2/14/08
1-1-24 Navigation Aids
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.
1-1-16. VHF Direction Finder
a. The VHF Direction Finder (VHF/DF) is one of
the common systems that helps pilots without their
being aware of its operation. It is a ground-based
radio receiver used by the operator of the ground
station. FAA facilities that provide VHF/DF service
are identified in the A/FD.
b. The equipment consists of a directional antenna
system and a VHF radio receiver.
c. The VHF/DF receiver display indicates the
magnetic direction of the aircraft from the ground
station each time the aircraft transmits.
d. DF equipment is of particular value in locating
lost aircraft and in helping to identify aircraft on
radar.
REFERENCEAIM,
Direction Finding Instrument Approach Procedure,
Paragraph6-2-3.
1-1-17. Inertial Reference Unit (IRU),
Inertial Navigation System (INS), and
Attitude Heading Reference System (AHRS)
a. IRUs are self-contained systems comprised of
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