Flight Management, Navigation -Navigation Systems Description

IRS Instrument Transfer Switch Schematic

Radio Navigation Systems Automatic Direction Finding (ADF)
An automatic direction finding (ADF) system enables automatic determination of magnetic and relative bearings to selected facilities.
YA721 - YA809, YC411 - YD655 Two ADF receivers are installed. The ADF bearing signals are sent to the pointers on the DUs and the standby radio magnetic indicator. The audio is heard by using the ADF receiver control on the audio selector panel.
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June 1, 2005  11.20.7
Flight Management, Navigation -Navigation Systems Description 737 Flight Crew Operations Manual

YA613 - YA687, YC153, YC154, YK101 - YK104 One ADF receiver is installed. The ADF bearing signal is sent to the pointer on the DUs and the standby radio magnetic indicator. The audio is heard by using the ADF receiver control on the audio selector panel.
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.”
Copyright . The Boeing Company. See title page for details.
11.20.8  March 28, 2005

Flight Management, Navigation -Navigation Systems Description 737 Flight Crew Operations Manual
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.
Marker Beacon
Marker beacon indications for outer, middle and inner marker are displayed on the upper right hand corner of the attitude display located on the Captain’s and First Officer’s Primary Flight Display (PFD) units.
Very High Frequency Omni Range (VOR)
Two VOR receivers are installed.
The flight crew must manually tune the VOR on the navigation control panel for

display on the DUs and the standby radio magnetic indicator. VOR–DME radio
updating is available if the crew manually tunes a valid in–range VOR station.
Left and right VOR bearings are displayed on the DUs when a valid in–range

VOR station is tuned and the respective EFIS control panel VOR/ADF switch is
in the VOR position. The DUs also show course deviation.

VHF NAV Transfer Switch
Should either VOR receiver fail, the VHF NAV transfer switch enables selection of the opposite VHF NAV receiver for display.
ATC Transponder
Two ATC transponders are installed and controlled by a single control panel. The ATC transponder system transmits a coded radio signal when interrogated by ATC ground radar. Altitude reporting capability is provided.
　
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