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Pilot's Handbook of Aeronautical Knowledge

Radio Navigation

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




The preceding are methods of computing approximate time
and distance. The accuracy of time and distance checks is
governed by existing wind, degree of bearing change, and
accuracy of timing. The number of variables involved causes
the result to be only an approximation. However, by flying an
accurate heading and checking the time and bearing closely,
the pilot can make a reasonable estimate of time and distance
from the station.

Course Intercept
Course interceptions are performed in most phases of
instrument navigation. The equipment used varies, but an
intercept heading must be flown that results in an angle or
rate of intercept sufficient to solve a particular problem.

Rate of Intercept
Rate of intercept, seen by the aviator as bearing pointer or
HSI movement, is a result of the following factors:
• The angle at which the aircraft is flown toward a
desired course (angle of intercept)
• True airspeed and wind (GS)
• Distance from the station

Angle of Intercept
The angle of intercept is the angle between the heading of the
aircraft (intercept heading) and desired course. Controlling
this angle by selection/adjustment of the intercept heading
is the easiest and most effective way to control course
interceptions. Angle of intercept must be greater than the
degrees from course, but should not exceed 90°. Within this
limit, adjust to achieve the most desirable rate of intercept.

When selecting an intercept heading, the key factor is the
relationship between distance from the station and degrees
from the course. Each degree, or radial, is 1 NM wide at
a distance of 60 NM from the station. Width increases or
decreases in proportion to the 60 NM distance. For example,
1 degree is 2 NM wide at 120 NM—and ½ NM wide at 30
NM. For a given GS and angle of intercept, the resultant rate
of intercept varies according to the distance from the station.
When selecting an intercept heading to form an angle of
intercept, consider the following factors:
• Degrees from course
• Distance from the station
• True airspeed and wind (GS)

Distance Measuring Equipment (DME)
Distance measuring equipment (DME) consists of an ultra
high frequency (UHF) navigational aid with VOR/DMEs and
VORTACs. It measures, in NM, the slant range distance of
an aircraft from a VOR/DME or VORTAC (both hereafter
referred to as a VORTAC). Although DME equipment is very
popular, not all aircraft are DME equipped.

To utilize DME, the pilot should select, tune, and identify
a VORTAC, as previously described. The DME receiver,
utilizing what is called a "paired frequency" concept,
automatically selects and tunes the UHF DME frequency
associated with the VHF VORTAC frequency selected by
the pilot. This process is entirely transparent to the pilot.
After a brief pause, the DME display shows the slant range
distance to or from the VORTAC. Slant range distance is the
direct distance between the aircraft and the VORTAC, and
is therefore affected by aircraft altitude. (Station passage
directly over a VORTAC from an altitude of 6,076 feet above
ground level (AGL) would show approximately 1.0 NM on
the DME.) DME is a very useful adjunct to VOR navigation.
A VOR radial alone merely gives line of position information.
With DME, a pilot may precisely locate the aircraft on that
line (radial).

Most DME receivers also provide GS and time-to-station
modes of operation. The GS is displayed in knots (NMPH).
The time-to-station mode displays the minutes remaining to
VORTAC station passage, predicated upon the present GS.
GS and time-to-station information is only accurate when
tracking directly to or from a VORTAC. DME receivers
typically need a minute or two of stabilized flight directly to
or from a VORTAC before displaying accurate GS or time to-
station information.

Some DME installations have a hold feature that permits
a DME signal to be retained from one VORTAC while the
course indicator displays course deviation information from
an ILS or another VORTAC.

Area navigation (RNAV) permits electronic course guidance
on any direct route between points established by the pilot.
While RNAV is a generic term that applies to a variety of
navigational aids, such as LORAN-C, GPS, and others, this
section deals with VOR/DME-based RNAV. VOR/DME
RNAV is not a separate ground-based NAVAID, but a
method of navigation using VOR/DME and VORTAC
signals specially processed by the aircraft's RNAV computer.
[Figure 15-34]

NOTE: In this section, the term "VORTAC" also includes

In its simplest form, VOR/DME RNAV allows the pilot to
electronically move VORTACs around to more convenient
locations. Once electronically relocated, they are referred
to as waypoints. These waypoints are described as a
combination of a selected radial and distance within the
service volume of the VORTAC to be used. These waypoints
allow a straight course to be flown between almost any
origin and destination, without regard to the orientation of
VORTACs or the existence of airways.