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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

Function of VOR

The VOR does not account for the aircraft heading. It only
relays the aircraft direction from the station and will have the
same indications regardless of which way the nose is pointing.
Tune the VOR receiver to the appropriate frequency of the
selected VOR ground station, turn up the audio volume, and
identify the station's signal audibly. Then, rotate the OBS
to center the CDI needle and read the course under or over
the index.

In Figure 7-12, 360° TO is the course indicated, while in
Figure 7-15, 180° TO is the course. The latter indicates that
the aircraft (which may beheading in any direction) is, at this
moment, located at any point on the 360° radial (line from
the station) except directly over the station or very close to
it, as in Figure 7-15. The CDI will deviate from side to side
as the aircraft passes over or nearly over the station because
of the volume of space above the station where the zone of
confusion exists. This zone of confusion is caused by lack of
adequate signal directly above the station due to the radiation
pattern of the station's antenna, and because the resultant

of the opposing reference and variable signals is small and
constantly changing.

The CDI in Figure 7-15 indicates 180°, meaning that the
aircraft is on the 180° or the 360° radial of the station. The TO/
FROM indicator resolves the ambiguity. If the TO indicator is
showing, then it is l~ 80° TO the station. The FROM indication
indicates the radial of the station the aircraft is presently on.
Movement of the CDI from center, if it occurs at a relatively
constant rate, indicates the aircraft is moving or drifting off the
180°/360° line. If the movement is rapid or fluctuating, this
is an indication of impending station passage (the aircraft is
near the station). To determine the aircraft's position relative
to the station, rotate the OBS until FROM appears in the
window, and then center the CDL needle. The index indicates
the VOR radial where the aircraft is located. The inbound (to
the station) course is the reciprocal of the radial.

If the VOR is set to the reciprocal of the intended course,
the CDI will reflect reverse sensing. To correct for needle
deflection, turn away from the needle. To avoid this reverse
sensing situation, set the VOR to agree with the intended

An HSI display as seen on the pilot’s primary flight display (PFD)
Figure 7-14. An HSI display as seen on the pilot's primary flight display (PFD), on an electronic flight instrument. Note that only attributes related to the HSI are labeled.