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unforecasted uncertainties for commercial use on an
uninterrupted basis.
As a result of these and other key factors, it was determined that
LORAN would remain. In recognition of GPS vulnerabilities
as a GNSS, there are plans to maintain other systems that
could provide en route and terminal accuracy such as LORAN.
Therefore as LORAN is further modernized it’s a possibility
that it may be used to augment GPS and provide backup to
GPS during unlikely but potential outages. Or if combined
with GPS and other systems such as newer miniaturized lowcost
inertial navigation systems (INS), superior accuracy and
seamless backup will always be available.
LORAN Components
The LORAN receiver incorporates a radio receiver, signal
processor, navigation computer, control/display, and antenna.
When turned on, the receivers go through an initialization
or warm-up period, then inform the user they are ready to
be programmed. LORAN receivers vary widely in their
appearance, method of user programming, and navigation
information display. Therefore, it is necessary to become
familiar with the unit, including programming and output
interpretation. The LORAN operating manual should be in the
aircraft at all times and available to the pilot. IFR-approved
LORAN units require that the manual be aboard and that the
pilot be familiar with the unit’s functions, before flight.
7-26
Figure 7-27. A typical example (GNS 480) of a stand-alone GPS
receiver and display.
Function of LORAN
After initialization, select for the present location WP
(the airport), and select GO TO in order to determine if
the LORAN is functioning properly. Proper operation is
indicated by a low distance reading (0 to 0.5 NM). The
simplest mode of navigation is referred to as GO TO: you
select a WP from one of the databases and choose the
GO TO mode. Before use in flight, verify that the latitude
and longitude of the chosen WP is correct by reference to
another approved information source. An updatable LORAN
database that supports the appropriate operations (e.g., en
route, terminal, and instrument approaches) is required when
operating under IFR.
In addition to displaying bearing, distance, time to the WP,
and track and speed over the ground, the LORAN receiver
may have other features such as flight planning (WP
sequential storage), emergency location of several nearest
airports, vertical navigation capabilities, and more.
LORAN Errors
System Errors
LORAN is subject to interference from many external
sources, which can cause distortion of or interference with
LORAN signals. LORAN receiver manufacturers install
“notch filters” to reduce or eliminate interference. Proximity
to 60 Hz alternating current power lines, static discharge,
P-static, electrical noise from generators, alternators, strobes,
and other onboard electronics may decrease the signalto-
noise ratio to the point where the LORAN receiver’s
performance is degraded.
Proper installation of the antenna, good electrical bonding,
and an effective static discharge system are the minimum
requirements for LORAN receiver operation. Most receivers
have internal tests that verify the timing alignment of the
receiver clock with the LORAN pulse, and measure and
display signal-to-noise ratio. A signal will be activated to alert
the pilot if any of the parameters for reliable navigation are
exceeded on LORAN sets certified for IFR operations.
LORAN is most accurate when the signal travels over sea
water during the day and least accurate when the signal
comes over land and large bodies of fresh water or ice at
night; furthermore, the accuracy degrades as distance from
the station increases. However, LORAN accuracy is generally
better than VOR accuracy.
Operational Errors
Some of the typical pilot-induced errors of LORAN operation
are:
1. Use of a nonapproved LORAN receiver for IFR
operations. The pilot should check the aircraft’s POH/
AFM LORAN supplement to be certain the unit’s
functions are well understood (this supplement must
be present in the aircraft for approved IFR operations).
There should be a copy of FAA Form 337, Major
Repair and Alteration, present in the aircraft’s records,
showing approval of use of this model LORAN for
IFR operations in this aircraft.
2. Failure to double-check the latitude/longitude values
for a WP to be used. Whether the WP was accessed
from the airport, NDB, VOR, or intersection database,
the values of latitude and longitude should still be
checked against the values in the A/FD or other
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