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by aircraft attitude or heading. [Figure 7-10] Radials can
be envisioned to be like the spokes of a wheel on which the
aircraft is on one specific radial at any time. For example,
aircraft A (heading 180°) is inbound on the 360° radial; after
crossing the station, the aircraft is outbound on the 180°
radial at A1. Aircraft B is shown crossing the 225° radial.
Similarly, at any point around the station, an aircraft can be
located somewhere on a specific VOR radial. Additionally,
a VOR needle on an RMI will always point to the course
that will take you to the VOR station where conversely the
ADF needle points to the station as a RB from the aircraft. In
the example above, the ADF needle at position A would be
pointed straight ahead, at A1 to the aircraft’s 180° position
(tail) and at B, to the aircraft’s right.
The VOR receiver measures and presents information to
indicate bearing TO or FROM the station. In addition to the
navigation signals transmitted by the VOR, a Morse code
signal is transmitted concurrently to identify the facility, as
well as voice transmissions for communication and relay of
weather and other information.
VORs are classified according to their operational uses. The
standard VOR facility has a power output of approximately
200 watts, with a maximum usable range depending upon
7-11
OBS
N E
S W
3
33
24
21
15
12
30
6
FR
TO NAV
OBS knob
CDI needle
Course index
Unreliable signal flag
FROM indicator
Approximately 2 degrees
in the VOR mode
TO indicator
Figure 7-12. The VOR Indicator Instrument.
Figure 7-11. VOR Transmitter (Ground Station).
Figure 7-13. A Typical Horizontal Situation Indicator (HSI).
MHz is in even-tenth increments to preclude any conflict
with ILS localizer frequency assignment, which uses the
odd tenths in this range.
The airborne equipment includes an antenna, a receiver, and
the indicator instrument. The receiver has a frequency knob to
select any of the frequencies between 108.0 to 117.95 MHz.
The On/Off/volume control turns on the navigation receiver
and controls the audio volume. The volume has no effect on
the operation of the receiver. You should listen to the station
identifier before relying on the instrument for navigation.
VOR indicator instruments have at least the essential
components shown in the instrument illustrated in
Figure 7-12.
Omnibearing Selector (OBS)
The desired course is selected by turning the OBS knob until
the course is aligned with the course index mark or displayed
in the course window.
Course Deviation Indicator (CDI)
The deviation indicator is composed of an instrument face
and a needle hinged to move laterally across the instrument
face. The needle centers when the aircraft is on the selected
radial or its reciprocal. Full needle deflection from the center
position to either side of the dial indicates the aircraft is 12°
or more off course, assuming normal needle sensitivity. The
outer edge of the center circle is 2° off course; with each dot
representing an additional 2°.
TO/FROM Indicator
The TO/FROM indicator shows whether the selected course
if intercepted and flown will take the aircraft TO or FROM
the station. It does not indicate whether the aircraft is heading
to or from the station.
Flags or Other Signal Strength Indicators
The device that indicates a usable or an unreliable signal may
be an “OFF” flag. It retracts from view when signal strength
is sufficient for reliable instrument indications. Alternately,
insufficient signal strength may be indicated by a blank or
OFF in the TO/FROM window.
The indicator instrument may also be a horizontal situation
indicator (HSI) which combines the heading indicator
and CDI. [Figure 7-13] The combination of navigation
information from VOR/Localizer (LOC) or from LORAN
or GPS, with aircraft heading information provides a visual
picture of the aircraft’s location and direction. This decreases
pilot workload especially with tasks such as course intercepts,
flying a back-course approach, or holding pattern entry. (See
7-12
XPDR 5537 IDNT LCL10:12:34
INSET PFD CDI XPDR IDENT TMR/REF NRST ALERTS
VOR 1
270°
HDG 270° CRS 270°
2
1
1
2
500
5300
5200
5100
5000
4900
4800
4300
20
80
5040
5000
130
120
90
1
100
9
TAS 106KT
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Instrument Flying Handbook仪表飞行手册下(15)
