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If the track of the aircraft is known more accurately than the GS, the course line should be adjusted since
any error in the GS will have little effect on it. If, however, you desire to adjust a speed line under these
conditions, the accuracy of the fix is in doubt. Similarly, if the GS is known more accurately than the
track, the speed line should be adjusted to the time of the course line. The line which will be affected
least by the information in doubt is the line which should be adjusted.
Section 5C— Radio Aids
5.8. Basics. Radio aids are ground based navigation facilities that transmit electronic signals received by
airborne units. Radio aids can be used for departure, en route navigation or arrivals, and procedures for
obtaining and plotting a fix vary by category. Explanations of different types of radio aids and how to
fix with them follow.
5.9. Nondirectional Radio Beacon (NDB). This is a low, medium, or ultra high frequency (UHF) radio
beacon which transmits nondirectional signals whereby the user can determine a bearing and home to
the station. NDBs normally operate in the frequency band of 190 to 535 kilocycles (kHz) and transmit a
continuous carrier with either 400 or 1020 cycles per second (Hz) modulation. All radio beacons, except
156 AFPAM11-216 1 MARCH 2001
the compass locators, transmit a continuous three-letter identification code except during voice
transmissions.
5.9.1. Disturbance. They are subject to disturbances that may result in erroneous bearing information.
Such disturbances result from intermittent or unpredictable signal propagation due to such factors as
lightning, precipitation, static, etc. At night, radio beacons are vulnerable to interference from distant
stations. Nearly all disturbances that affect the automatic direction finder (ADF) bearing also affect the
facility's identification. Noisy identification usually occurs when the ADF needle is erratic. Voice,
music, or erroneous identification will usually be heard when a steady false bearing is being displayed.
Since ADF receivers do not have a flag to warn the user when erroneous bearing information is being
displayed, the NDB's identification should be continuously monitored.
5.9.2. Control Panels. There are several different types of control panels currently installed in Air Force
aircraft. Refer to aircraft technical manuals for specific guidance pertaining to equipment operation.
5.10. Plotting on a Chart. Before an ADF bearing can be plotted on a navigation chart, two things must
be done. First, the bearing obtained must be converted to a true bearing (TB). If a nonrotatable compass
card is used, the resultant RB may be converted to TB by adding the aircraft true heading (TH) (TH +
RB = TB). If a rotatable compass card is used, the TB can be found by applying the magnetic variation
at the vicinity of the aircraft.
5.11. Ultra High Frequency (UHF) Direction Finders (DF). Some aircraft are equipped with ADFs in
the UHF frequency range (225.0–399.9 mHz) which utilize loop and sensing (antennas) to give bearing
information. Operation of the DF is controlled from the UHF radio panel. It is used to obtain bearing to
other aircraft and to emergency locator beacons.
5.12. VHF Omnidirectional Range (VOR). VOR stations operate between 108.00 and 117.95
megacycles per second (mHz). VHF communications operate between 118.00 and 135.90 mHz. Station
identifiers for VOR NAVAIDs are given in code or voice, or by alternating code and voice
transmissions. VOR transmissions are limited by line of sight (LOS) and a combination of aircraft
altitude and distance to the station. Accurate information may be obtained from 40 to 100 NM around
the facility, although the usable range may be much greater (300 NM). VOR may be used by flying
courses from one station to another as part of the high or low jet navigation airways system. It may be
used as a fixing aid by taking a bearing and applying magnetic variation at the station (converting
magnetic bearing [MB] to TB) and plotting an LOP. In aircraft equipped with two VORs, the bearings to
two different stations may be taken simultaneously and plotted, and a fix position obtained. The aircraft
is directly overflying a VOR when the bearing pointer drops rapidly below the 3 or 9 o'clock position.
5.12.1. Control Panel. A VOR control panel contains (1) a power switch, (2) frequency window, (3)
volume control, (4) equipment self-test capability, and (5) frequency selector controls. All are shown in
Figure 5.7. To tune a VOR, turn power switch to PWR, select desired frequency and identify the station.
For positive test indications, consult applicable aircraft technical order.
5.12.2. Indicator Panel. Several types of indicators exist which display VOR information. Examples
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