737 Flight Crew Operations Manual
Flight Management, Navigation -
Navigation Systems Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
11.20.8 D6-27370-866-EGP
If heading or track information is lost or invalid, ADF bearing pointers on the DUs
will be removed, and ADF bearing pointers on the standby radio magnetic
indicator will not display correct magnetic bearing. Relative bearings indicated by
pointers may be correct if the receiver is operating.
Distance Measuring Equipment (DME)
Two frequency scanning DME systems are installed.
The FMC autotunes DME receivers as necessary for position updating. During
normal operations, two different DME signals or a signal from a collocated
VOR/DME pair provide an accurate radio geographical position to the FMC. The
identifiers of DMEs currently providing update data to the FMC are displayed on
the NAV STATUS page 1/2. The radio position is displayed on the POS REF page
2/3. Specific DME station tuning for FMC position updating can be inhibited on
the NAV OPTIONS page 2/2.
The flight crew must manually tune the DME on the VHF navigation control panel
and the respective EFIS control panel VOR/ADF switch must be in the VOR
position for DME to be displayed on the CDS. DME distance is also displayed on
the CDS when the ILS receivers are tuned to a collocated DME and localizer
facility.
Instrument Landing System (ILS)
Two ILS receivers are installed.
The ILS receivers are tuned manually on the VHF navigation control panel. The
flight crew must manually tune the ILS for display on CDS. The ILS localizer and
glideslope can also be displayed on the standby attitude indicator.
LOC updating of the FMC occurs only after the ILS is manually tuned.The tuned
ILS frequency is displayed on the navigation display in the APP modes.
Navaid Identifier Decoding
The Morse code identifier of a tuned VOR, ILS, or ADF can be converted to alpha
characters. The decoded identifier is then shown on the PFD and ND. The crew
should monitor this identifier for correct navigation radio reception. The identifier
name is not compared with the FMC database.
Due to the large variation in ground station identifier quality, the decode feature
may incorrectly convert the intended identifier name. Examples: the Hong Kong
localizer “KL” may show as “KAI,” or the Boeing Field ILS may show as “QBFI”
or “TTTT” instead of “IBFI.”
Pilots should verify the identity of the tuned navigation station from the audio
Morse code when the tuned frequency remains shown or an incorrect identifier is
shown.
September 28, 2006
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