G5 HSI CDI deflection under VLOC

Discussion in 'Cleared for the Approach' started by sarangan, Nov 2, 2019.

  1. sarangan

    sarangan Line Up and Wait

    Joined:
    Jun 7, 2008
    Messages:
    696
    Location:
    Dayton, OH
    Display Name:

    Display name:
    Andrew Sarangan, CFII
    I am somewhat new to the G5, and I've been having some issues with the G5 HSI. Under VLOC, I am not getting the green CDI needle unless I am within about 10-deg of the selected course. No CDI needle makes makes me think we are not receiving any signal. But I can receive it just fine with the NAV2 radio which is tied to a traditional CDI (which shows a full scale deflection, as expected). Under GPS mode, however, the HSI shows a CDI no matter how far off the selected course I am. So this behavior seems specific to VLOC only. Has anyone else experienced this?
     
  2. Landing Fees

    Landing Fees Pre-takeoff checklist

    Joined:
    Feb 9, 2018
    Messages:
    387
    Display Name:

    Display name:
    Landing Fees
    The full-scale limits for the CDI are defined by a GPS-derived distance when coupled to GPS. When coupled to a VOR or localizer (LOC), the CDI has the same angular limits as a mechanical CDI.

    If you are outside of 10° you shouldn’t pick it up correct?
     
  3. sarangan

    sarangan Line Up and Wait

    Joined:
    Jun 7, 2008
    Messages:
    696
    Location:
    Dayton, OH
    Display Name:

    Display name:
    Andrew Sarangan, CFII
    I was expecting it to show full scale deflection when the deviation is more than 10 deg, just like the old mechanical CDI. Instead, it seems to show no CDI. That makes it difficult to figure out which side the course lies.
     
  4. Landing Fees

    Landing Fees Pre-takeoff checklist

    Joined:
    Feb 9, 2018
    Messages:
    387
    Display Name:

    Display name:
    Landing Fees
    That is what we have iPads, GNS/GTNs and near 100% radar coverage...so we don't have to guess anymore.
     
  5. N1120A

    N1120A Line Up and Wait

    Joined:
    Apr 24, 2018
    Messages:
    882
    Location:
    AG5B MYF
    Display Name:

    Display name:
    N1120A
    The logic is that you use GPS until you're close enough to start getting sensitivity..