BY ORDER OF THE SECRETARY OF THE AIR FORCE AIR FORCE ...

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AFMAN 11-217V1 3 JANUARY 2005
markers, it is called a "compass locator." Sometimes the low-powered NDB [i.e.
compass locator] will be a stand alone NAVAID with limited range (usually less than 15
miles). These locators may be identified by an “L” and the use of the two-digit identifier.
6.11.3. Identification. Most radio beacons within the U.S. transmit a continuous threeletter
identifier. A two-letter identifier is normally used in conjunction with an ILS.
Some NDBs have only a one-letter identifier. Outside of the contiguous U.S., one, two,
or three-letter identifiers are transmitted; for example, BB.
6.11.4. Voice Transmissions. Voice transmissions can be made on radio beacons unless
the letter "W" (without voice) is included in the class designator (HW).
6.11.5. Disturbances. Radio beacons 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 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.
6.11.5.1. WARNING: Since ADF receivers do not have a "flag" to warn the pilot
when erroneous bearing information is being displayed, the pilot must continuously
monitor the NDBs identification.
6.11.6. Control Panels. There are several different types of control panels currently
installed in our operational aircraft. Refer to your aircraft technical manual for specific
guidance pertaining to equipment operation and its limitations.
6.11.6.1. NOTE: ADF course intercept procedures are basically the same as those
used in VOR/RMI-only procedures.
6.12. Global Positioning System (GPS).
6.12.1. GPS Capabilities.
6.12.1.1. Spaced Based System. GPS is a space based navigation system that has the
capability to provide highly accurate three-dimensional position, velocity, and time to
an infinite number of equipped users anywhere on or near the Earth (Figure 6.8).
The typical GPS integrated system will provide: position, velocity, time, altitude,
steering information, groundspeed and ground track error, heading, and variation.
GPS also provides a constant monitor of system status and accuracy, and the built-in
test circuitry provides self-tests that diagnose most system failures. The airborne
GPS receiver may accept inputs from other aircraft systems, such as INS, altimeter,
central air data computer (CADC), attitude gyro, and compass systems that improve
GPS accuracy and reliability. GPS may also be integrated into a multi-sensor
navigation system combining GPS information with other sources such as an Inertial
Reference Unit (IRU) or DME/DME Area Navigation (RNAV) equipment.
6.12.1.2. Position Determination. GPS position determination is based on the
concept of ranging and triangulation from a group of satellites in space acting as
precise reference points. A GPS receiver measures distance from a satellite using the
travel time of a radio signal. Each satellite transmits a specific code, called a coarse