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LPV degraded during final approach segment

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Aircraft Systems, Instrument Rating

Good evening,

I have a theoretical question. During my IF training I learned that any time my GNSS receiver shows integrity issues during an RNAV (GNSS) approach, I shall initiate the missed approach procedure. So, if the receiver does not switch APPR active mode or returns to TERM mode once on the final descent to LNAV MDA, I must go around.

I am now studying about EGNOS-augmented approaches, such as LPV. Once I am on the glideslope by the receiver's LPV mode, is it possible that EGNOS fails for any reason but LNAV integrity remains? If so, is it possible and legal that I continue my approach to LNAV MDA (just like when there's an ILS GP outage and I go on with LOC minima)? I am interested in either European, FAA or Canadian rules as well, if they are different.

Thanks in advance.

Andy

 

2 Answers



  1. John D Collins on Sep 22, 2018

    This is covered in the AFMS for the navigation system. Here is what the GTN series says:

    3.2.2 GPS APPROACH DOWNGRADE
    During a LPV, LP +V, LNAV/VNAV, or LNAV +V approach, if GPS accuracy requirements cannot be met by the GPS receiver, the GTN will downgrade the approach. The downgrade will remove vertical deviation indication from the VDI and change the approach annunciation to LNAV. The approach may be continued using the LNAV only minimums. If the VISUAL approach is downgraded, the GTN will remove the vertical deviation indication from the VDI, but continue to annunciate VISUAL in amber.

    During a GPS approach in which GPS accuracy requirements cannot be met by the GPS receiver for any GPS approach type, the GTN will flag all CDI guidance and display a system message “ABORT APPROACH-GPS approach no longer available”. Immediately upon viewing the message, the unit will revert to Terminal navigation mode alarm limits. If the position integrity is within these limits lateral guidance will be restored and the GPS may be used to execute the missed approach, otherwise alternate means of navigation must be utilized.

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  2. VS461 on Sep 25, 2018

    Thank you, Sir!

    Andy

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