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 updateable 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 hearing, 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 manufactures 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 signal-
to-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 is 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 is
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 unapproved LORAN receiver for IFR
operations. The pilot should cheek 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
approved source. If the WP data is entered in the user
database, its accuracy must be checked before use.

3. Attempting to use LORAN information with degraded
signals.

Advanced Technologies

Global Navigation Satellite System (GNSS)
The Global Navigation Satellite System (GNSS) is a
constellation of satellites providing a high-frequency signal
which contains time and distance that is picked up by a
receiver thereby. [Figure 7-27] The receiver, which picks up
multiple signals from different satellites is able to triangulate
its position from these satellites.

Figure 7-27. A typical example (GNS 480) of a stand-alone GPS
receiver and display.