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MH) you see the needle has drifted to first dot on the right. This first dot represents a 5° deviation from the radial.
What do you do to correct for the wind drift, and get back on course? If you said, change the OBS to 100°,
WRONG!. Do not change the OBS, because that is the Magnetic Course (MC) of 095° is what you want to
track over the ground.
Rather , change your magnetic heading to the right, say 10°, to a MH of 105°. Hold that for a while. If the needle
drift ceases (it steadies), you are now flying parallel to your course, but to the left of course. You now need to get
back on course, so take another 10° correction to the right (now a 20° total correction) to a MH of 115°. When
the needle comes back to center, you are back on the desired radial. Now remove that last 10° correction (i.e.
come back to a Magnetic Heading (MH) of 105°). That should now hold you approximately on the 095° radial by
holding a 10° right Wind Correction Angle (WCA) (i.e. holding a 105° MH on the compass).
However, if the initial 10° R WCA fails to stop the needle from drifting right, increase the WCA to 20° R
(MH=115°). If the needle steadies, increase the MH to 120-130° to get back on course, then hold a 20° WCA
(MH=115°). Maintain this for a while to see if that holds the needle centered.
Continue to make this type of correction, left or right until you have the correct WCA pinned down to hold you
"on course" with needle remaining centered. Usually when flying cross country, you do not make large radial
changes; so the WCA you held on the last leg should be close to appropriate for the next leg. After some practice,
you will be able to estimate the WCA fairly quickly by watching how fast the needle drifts from center.
Testing the VOR Indicator for Accuracy
Generally, the accuracy of the VOR is within one degree. However, due to age or other factors, the error may
increase. The accuracy of a VOR receiver can be checked several ways.
· FAA VOR Test Facilities (VOT)
· Airborne Check Points
· Ground Check Points
The Airport/Facility Directory is a document describing all public airports and navigational facilities. It can be
purchased at most airports and pilot supply stores for a nominal fee. This document lists certified checkpoints that
may be used to check VOR Receiver accuracy. These are selected ground or in-flight checkpoints which have a
known radial bearing from the specified VOR.
The FAA VOR Test facility is called a VOT. These facilities are usually found at larger airports. It is a special
test facility which can be tuned while on the ground at the airport. When you tune the VOT frequency, you will
hear a series of dots, or a steady tone as the VOT identifier. Turn the OBS until the CDI centers. The course
indicator should read either 0° or 180°. If 180°, the flag should be TO. If the OBS reads 0°, the flag should be
FROM.
The OBS reading must be accurate to +/- 4 degrees for ground based checkpoints and +/- 6° for airborne
checkpoints..
For mor information on VOR testing procedures, consult AIM 1-4. VOR RECEIVER CHECK
Using VOR Intersections
Navigation
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You can determine your position by using a radial readinreceiver to one of the stations. Rotate the OBS knob ustation. Draw a line from the center of the the VOR comof the compass rose). Now do the same for the radial reposition at the time the readings were made. For best In the example, you read a radial of 150° from the top VOR, and 060° from the lower VOR. By drawing lines on
the chart representing these radials, you are at the intersection of the lines. Often, where Victor Airways cross, the
intersection will be indicated on the chart by crossed arrows and an intersection name.
Distance Measuring Equipment (DME)
VOR/DME and VORTAC stations provide distance information for aircraft equipped with Distance Measuring
Equipment (DME). DME operates in the UHF radio band on frequencies from 962 MHz to 1213 MHz. Whenever
you tune the VOR station frequency, the DME receiver automatically selects the correct UHF frequency. This is
called “paired frequency selection”. The pilot need not be concerned with the UHF frequency.
Some DME systems can also be “slaved” from a normal VOR receiver, so that the DME automatically operates
on the VOR station selected by the VOR receiver. Tuning a DME receiver is similar to tuning the VOR receiver;
i.e. the frequency of the VOR is selected on the DME tuner dials.
The DME unit uses a “shark fin” appearing antenna, normally mounted underneath the aircraft. The aircraft DME
　
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