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A couple of questions

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  • A couple of questions

    1) What exactly is the relationship between an FMS and an NDB? Do they at all interact? If so, when?
    2) Why does the GPWS gets ADC and CAS (220747)? The mode 1 warning gets it's input from the rad alt, does it not? I can't think of any other use the GPWS would have for ADC data.
    Thank you

  • #2
    Hello.

    On the Classic 737 the NDBs are manually tuned through the ADF Controller on the centre pedestal. With the VOR/ADF switch on the EFIS Control Panel selected on, and a valid ADF signal received the bearing information will be presented on the EHSI in the form of a needle (in NAV Mode). Alternatively if MAP mode is selected on the EFIS Control a triangle NAV AID icon will depict the NDB and it's relative bearing. So we have the ADF signals fed to the EHSI's via the symbol generator.
    On more modern aircraft, depending on fit, the ADF controller remains but also the FMS MCDU can be used to tune the ADF's, accessed through the FMC COMM menu.

    Mode 1 GPWS is active below 2500' Rad Alt. Should an excessive BAROMETRIC rate of descent develop for the aircraft's current height above ground a GPWS warning will be triggered.
    Mode 4 " TOO LOW TERRAIN" or "TOO LOW GEAR/FLAP" requires Air speed and Configuration data to determine if the aircraft is in the approach phase or not. Hence at higher speeds if the terrain floor is breached a "TERRAIN" not "GEAR/FLAP" warning will be generated.

    Fraser.

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    • #3
      As always, thank you for the answer.

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