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0 10 20 30 40 50 60 70 80
OBS
N
E
S
W
3
33
24
21
15
1230
6
TO
33
30
24
2I
I5
I2
6
3
33
30
24
2I
I5
I2
6
3
OBS
N
E
S
W
3
33
24
21
15
12
30
6
TO
OBS
N
E
S
W
3
33
24
21
15
12
30
6
TO
33
30
24
2I
I5
I2
6
3
33
30
24
2I
I5
I2
6
3
OBS
N
E
S
W
3
33
24
21
15
12
30
6
TO
Figure 7-15. Course interpretation VOR.
• Take difference between
current radial of 160° and
desired radial 205° (45°)
• Double for intercept (90°)
• Add to desired radial
(205° + 90° = 295°)
• Turn to 295° until
interception of the 205°
radial
Interception
Determination
205° 025°
160°
295°
A
4
3
2
1
1
2
3
4
NOTES
1. View from pilot’s position
2. Movable-card is reset at
each turn
Figure 7-16. Course Interception (VOR).
7-16
VOR Accuracy
The effectiveness of the VOR depends upon proper use and
adjustment of both ground and airborne equipment.
The accuracy of course alignment of the VOR is generally
plus or minus 1°. On some VORs, minor course roughness
may be observed, evidenced by course needle or brief flag
alarm. At a few stations, usually in mountainous terrain,
the pilot may occasionally observe a brief course needle
oscillation, similar to the indication of “approaching station.”
Pilots flying over unfamiliar routes are cautioned to be on
the alert for these vagaries, and in particular, to use the TO/
FROM indicator to determine positive station passage.
Certain propeller revolutions per minute (RPM) settings
or helicopter rotor speeds can cause the VOR CDI to
fluctuate as much as plus or minus 6°. Slight changes to
the RPM setting will normally smooth out this roughness.
Pilots are urged to check for this modulation phenomenon
prior to reporting a VOR station or aircraft equipment for
unsatisfactory operation.
VOR Receiver Accuracy Check
VOR system course sensitivity may be checked by noting
the number of degrees of change as the OBS is rotated to
move the CDI from center to the last dot on either side. The
course selected should not exceed 10° or 12° either side. In
addition, Title 14 of the Code of Federal Regulations (14
CFR) part 91 provides for certain VOR equipment accuracy
checks, and an appropriate endorsement, within 30 days prior
to flight under IFR. To comply with this requirement and to
ensure satisfactory operation of the airborne system, use the
following means for checking VOR receiver accuracy:
1. VOR test facility (VOT) or a radiated test signal from
an appropriately rated radio repair station.
2. Certified checkpoints on the airport surface.
3. Certified airborne checkpoints.
VOR Test Facility (VOT)
The Federal Aviation Administration (FAA) VOT transmits
a test signal which provides users a convenient means to
determine the operational status and accuracy of a VOR
receiver while on the ground where a VOT is located.
Locations of VOTs are published in the A/FD. Two means of
identification are used. One is a series of dots and the other is
a continuous tone. Information concerning an individual test
signal can be obtained from the local flight service station
(FSS.) The airborne use of VOT is permitted; however, its
use is strictly limited to those areas/altitudes specifically
authorized in the A/FD or appropriate supplement.
To use the VOT service, tune in the VOT frequency 108.0
MHz on the VOR receiver. With the CDI centered, the
OBS should read 0° with the TO/FROM indication showing
FROM or the OBS should read 180° with the TO/FROM
indication showing TO. Should the VOR receiver operate an
RMI, it would indicate 180° on any OBS setting.
A radiated VOT from an appropriately rated radio repair
station serves the same purpose as an FAA VOT signal, and
the check is made in much the same manner as a VOT with
some differences.
The frequency normally approved by the Federal
Communications Commission (FCC) is 108.0 MHz;
however, repair stations are not permitted to radiate the
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