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I have a GPS receiver with WAAS. During an LPV approach, I received an LOI message That means I only lost WAAS, not RAIM. Did I just need to change minimum to LNAV and continue the approach?

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  • $\begingroup$ What avionics do you have? $\endgroup$
    – Chris
    Jan 2 at 7:25

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where were you at on the approach when you received the LOI message? This is my understanding:

  • Outside the FAF, adjust minimums as necessary for the new procedure (LNAV/VNAV or LNAV) depending on the mode the WAAS GPS fell down to.

  • Inside the FAF, immediately execute missed approach procedures.

The importance of a stabilized approach cannot be over-emphasized. If you are below 1,000 FT AGL on an instrument approach and something changes, it is often better to go-around than adjust to the change. Approach landing accident reduction (ALAR) research confirms the importance of a stabilized approach.

Having to switchfrom a vertically guided descent with a missed approach altitude set in the altitude alerter to a non-vertically guided approach where you must adjust the altitude alterter, and possibly flight director / autopilot modes below stabilized approach alititude could be unsafe in my opinion.

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  • $\begingroup$ I think the key point here is that this is your opinion. There is no way I would execute a missed just because I lost the capability of following vertical guidance. This is no different than flying an ILS and converting it to a LOC if the glideslope goes out. When cleared for the approach, you are cleared for all lines of minima. Also, do you have any links for non-commercial operations and ALAR? I haven’t yet found where this is applicable to either GA or military flying. $\endgroup$
    – Timbo
    Jan 2 at 11:49

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