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Instrument Flying Handbook
Navigation Systems
Traditional Navigation Systems

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Instrument Flying


Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Using an Electronic Flight

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency

A control panel from a military aircraft
Figure 7-26. A control panel from a military aircraft after LORAN
was first put into use. The receiver is remotely mounted and
weighs aver 25 pounds. Its size is about six times that of the
LORAN fully integrated receiver.

While continually computing latitude/longitude fixes, the
computer is able to determine and display:

1. Track over the ground since last computation;

2, Groundspeed by dividing distance covered since last
computation by the time since last computation (and
averaging several of these);

3. Distance to destination;

4. Destination time of arrival; and

5, cross-track error.

The Aeronautical Information Manual (AIM) provides a
detailed explanation of how LORAN works. LORAN is
a very accurate navigation system if adequate signals are
received. There are two types of accuracy that must be
addressed in any discussion of LORAN accuracy.

Repeatable accuracy is the accuracy measured when a user
notes the LORAN position moves away from that location,
then uses the LORAN to return to that initial LORAN
position. Distance from that initial position is the error.
Propagation and terrain errors will be essentially the same as
when the first position was taken, so those errors are factored
out by using the initial position. Typical repeatable accuracy
for LORAN can be as good as 0.01 NM, or 60 feet, if the
second position is determined during the day and within a
short period of time (a few days).

Absolute accuracy refers to the ability to determine present
position in space independently, and is most often used by
pilots. When the LORAN receiver is turned on and position
is determined, absolute accuracy applies. Typical LORAN
absolute accuracy will vary from about 0.1 NM to as much
as 2.5 NM depending on distance from the station geometry
of the TD LOP crossing angles, terrain and environmental
conditions, signal-to-noise ratio (signal strength), and sonic
design choices made by the receiver manufacturer.

Although LORAN use diminished with the introduction
of Global Navigation Satellite Systems such as the United
States' GPS, its use has since increased. Three items aided
in this resurgence:

  • In 1996, a commission called the Gore Commission
    evaluated GPS long-term use as a sole navigation
    aid. Although GPS was hailed originally as the
    eventual sole NAVAID, which would replace the need
    for most currently existing NAVAIDs by the year
    2020, the commission questioned single-link failure
    potential and its effect on the NAS. For this reason,
    the forecasted decommissioning of the VOR has been
    amended and their expectant lifecycle extended into
    the future. Additionally, the use of LORAN continues
    to be evaluated for facilitating carrying GPS corrective
    timing signals.
  • The GPS is controlled by the DOD presenting certain
    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 low-
cost 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 is familiar with the unit's functions, before flight.