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A320 ILS and non precision approach coding on FMS

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A320 ILS and non precision approach coding on FMS

Old 17th Sep 2021, 15:05
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A320 ILS and non precision approach coding on FMS

While using FINAL APP GUIDANCE, FCTM mentions to cross check the approach coded in the FMS against the chart; Eg. FPA, FDP, MAP etc. This action is clear since the FMS will be using barometric altitude for vertical guidance. However, I see that even an ILS approach is coded in the FMS similar to a non-precision approach. If the ILS is flown based on the ground based radio signals, what is the requirement for this approach to be coded in the FMS with an FPA and MAP?
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Old 17th Sep 2021, 18:20
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It's the same in Boeings. Basically it's there so that your pink string matches what you're doing, distance to run is correct etc, plus generally the missed approach would be flown in LNAV.
Also, if your LOC/APP button falls off and the pink string follows the approach accurately you can still fly the approach using the autopilot as an overlay approach: just monitor the raw data.
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Old 18th Sep 2021, 06:45
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I've always just considered it as basic error checking.
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Old 18th Sep 2021, 13:25
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I thought if the ILS receiver or transmitter is lost for a predetermined seconds, then the AP FD reverts to HDG V/S.
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Old 18th Sep 2021, 16:49
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No idea but that's not really the issue. If you've followed a pink string for 1000 miles to a 10 mile final at 3000' it would be a bit weird for that line to disappear only to pop up again at the MAP. Why would they not code the actual approach as well?
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Old 20th Sep 2021, 02:53
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Your understanding is correct.

LOC+G/S is used to fly the ILS signal, and there is no way to couple the LNAV or VNAV to FDs for an approach that is coded as ILS in the FMGS.

If the database legs finished at the GP intercept point, then a discontinuity followed until MAPt where the coding would resume, all the features we know should work as advertised in the FCOM regardless.

Yet it is coded there anyway. Not a problem.
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Old 20th Sep 2021, 06:26
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Originally Posted by FlightDetent View Post
LOC+G/S is used to fly the ILS signal, and there is no way to couple the LNAV or VNAV to FDs for an approach that is coded as ILS in the FMGS.
Is this an Airbus thing? In a Boeing you have to press LOC/APP otherwise it will stay in LNAV/VNAV for the approach.
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Old 20th Sep 2021, 11:31
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Yes, the setup of the buttons and functions is subtly different.

The 320 has VNAV-DES and VNAV-APCH as two standalone features. The VNAV-APCH (+LNAV) is armed with the APP push-button from the MCP.

If the selected approach in FMGS is ILS, however, that APP button will arm LOC and GS instead of LNAV+VNAV-APCH.

We do have a separate LOC button, but not a GS one.

I have no knowledge or experience with the more recent 'FLS' mode for APVs.
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Old 20th Sep 2021, 17:51
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Thank you all
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Old 22nd Sep 2021, 05:37
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Basically it's to check that you have programmed the desired ILS and also it's missed approach procedure. To fly the ILS part you may not need ILS programming but to fly the missed app automatically and to link the ILS again it needs to be in the MCDU.

Last edited by vilas; 22nd Sep 2021 at 07:55.
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Old 22nd Sep 2021, 12:28
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ok. thanks
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