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RAIM vs WAAS

Asked by: 2927 views FAA Regulations, Instrument Rating

So from my understanding that, we need at least 5 visible satellites in order to calculate RAIM. RAIM only calculates HPL(Horizontal protection Level) but WAAS does something even better; HPL + VPL(Vertical Protection Level).

Now from my understanding, WAAS stations receive L1, L2 Satellites information directly to calculate and generate WAAS message to further correct signal and shoot them to WAAS satellites.

My question is that why do we still get LOI on G1000 when we have less than 4 visible satellites when WAAS is on ? (even though WAAS further fine tunes the signal...)

Also, with WAAS, is WAAS technically doing RAIM + VPL calculation or HPL + VPL calculation? Does the techincal word 'RAIM' applicable to WAAS?

1 Answers



  1. Odai Ayyad on Apr 29, 2018

    Hi

    i believe that this helpful document shall answer your question and clearfay some of the information about the RAIM

    in short if you dont have RAIM you wont be able to shot the basic GPS approaches even the NON-Precision approaches and your gps might only be usable for VFR flying only in that case so if you can’t carry out GPS approaches on your GPS and then you can use it only for VFR i believe you should not even get a WAAS single to shot an LPV approach

    i am answering only based on the knowledge i have as i am only a CFI not a CFII so i recommend you to read that PDF in the link and also ask some one who holds a CFII

    http://www.fredonflying.com/Articles/IFR_Refresher/1209-RAIM-RAIM-Don't-Go-Away.pdf

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