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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




Flying an RNAV course.
Figure 15-34. Flying an RNAV course.

While the capabilities and methods of operation of VOR/
DME RNAV units differ, there are basic principles of
operation that are common to all. Pilots are urged to study
the manufacturer's operating guide and receive instruction
prior to the use of VOR/DME RNAV or any unfamiliar
navigational system. Operational information and limitations
should also be sought from placards and the supplement
section of the AFM/POH.

VOR/DME-based RNAV units operate in at least three
modes: VOR, en route, and approach. A fourth mode, VOR
Parallel, may also be found on some models. The units need
both VOR and DME signals to operate in any RNAV mode.
If the NAVAID selected is a VOR without DME, RNAV
mode will not function.

In the VOR (or non-RNAV) mode, the unit simply functions
as a VOR receiver with DME capability. [Figure 15-35] The
unit's display on the VOR indicator is conventional in all
respects. For operation on established airways or any other
ordinary VOR navigation, the VOR mode is used.

RNAV controls.
Figure 15-35. RNAV controls.

To utilize the unit's RNAV capability, the pilot selects and
establishes a waypoint or a series of waypoints to define
a course. To operate in any RNAV mode, the unit needs
both radial and distance signals; therefore, a VORTAC (or
VOR/DME) needs to be selected as a NAVAID. To establish
a waypoint, a point somewhere within the service range of
a VORTAC is defined on the basis of radial and distance.
Once the waypoint is entered into the unit and the RNAV en
route mode is selected, the CDI displays course guidance to
the waypoint, not the original VORTAC. DME also displays
distance to the waypoint. Many units have the capability to
store several waypoints, allowing them to be programmed
prior to flight, if desired, and called up in flight

RNAV waypoints are entered into the unit in magnetic
bearings (radials) of degrees and tenths (i.e., 275.5°) and
distances in NM and tenths (i.e., 25.2 NM). When plotting
RNAV waypoints on an aeronautical chart, pilots find it
difficult to measure to that level of accuracy, and in practical
application, it is rarely necessary. A number of flight planning
publications publish airport coordinates and waypoints with
this precision and the unit accepts those figures There is a
subtle, but important difference in CDI operation and display
in the RNAV modes.

In the RNAV modes, course deviation is displayed in terms
of linear deviation. In the RNAV en route mode, maximum
deflection of the CDI typically represents 5 NM on either side
of the selected course, without regard to distance from the
waypoint. In the RNAV approach mode, maximum deflection
of the CDI typically represents 1¼ NM on either side of the
selected course. There is no increase in CDI sensitivity as the
aircraft approaches a waypoint in RNAV mode.

The RNAV approach mode is used for instrument approaches.
Its narrow scale width (¼ of the en route mode) permits very
precise tracking to or from the selected waypoint. In visual
flight rules (VFR) cross-country navigation, tracking a course
in the approach mode is not desirable because it requires a
great deal of attention and soon becomes tedious.

A fourth, lesser-used mode on some units is the VOR Parallel
mode. This permits the CDI to display linear (not angular)
deviation as the aircraft tracks to and from VORTACs.
It derives its name from permitting the pilot to offset (or
parallel) a selected course or airway at a fixed distance of
the pilot's choosing, if desired. The VOR parallel mode
has the same effect as placing a waypoint directly over an
existing VORTAC. Some pilots select the VOR parallel
mode when utilizing the navigation (NAV) tracking function
of their autopilot for smoother course following near the