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4 Answers

What are the differences between GPS approach and LNAV approach in general?

Asked by: 4979 views Instrument Rating

If LPV and LNAV/VNAV consider as a WAAS approaches the GPS and LNAV looks the some


4 Answers

  1. John D. Collins on Oct 02, 2012

    There are approaches that are stand alone GPS or overlay GPS (example VOR or GPS). These approaches may be flown by an IFR GPS with or without WAAS. The RNAV (GPS) approaches can have LPV, or LP, or LNAV/VNAV, or LNAV minimums. The LNAV procedures are essentially the same as the original GPS approaches and can be flown by the same type of GPS (With or without WAAS). To fly the LPV, or LP procedures, the GPS has to be a WAAS TSO C146/145AR GPS system and the AFMS must permit these procedures to be flown. To fly the LNAV/VNAV procdure, either a WAAS TSO C146/145AR GPS or a Baro/VNAV system is permitted to fly them. If a RNAV (GPS) procedure has LPV, LNAV/VNAV, and LNAV minimums, a WAAS TSO C146/145AR system such as the GNS530W may fly any of the procedures. A non WAAS TSO C129a GPS that is IFR approved for approaches may only fly the LNAV procedure.

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  2. Brian on Oct 02, 2012

    LNAV is lateral navigation.
    VNAV is vertical navigation. Provide by a barometric system like you’re used to. Or by WAAS if you have the capability.
    RNAV is simply area navigation.

    WAAS is a GPS system that provides vertical guidance independent of a barometric system. It’s more advanced and allows for lower minimums on an approach. Similar to that of an ILS.

    See AIM 1-1-20 for the specifics.

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  3. Wes Beard on Oct 02, 2012

    The obstacle clearance for an LNAV is much greater than an approach with only LPV minimums. This means that approaches with LNAV minimas will typically keep you higher than one with only LPV minimums.

    The biggest difference, to me, is LNAV (and LNAV+V / LNAV/VNAV) the horizontal scaling is linear meaning the needle does not get more sensitive as the aircraft proceeds towards the runway like an ILS localizer does. The LPV horizontal scaling is angular almost the same as a localizer signal. This results in a much more accurate approach and landing on the intended runway.

    I blogged about the differences awhile ago here: http://allaboutairplanes.wordpress.com/2011/10/22/gps-approach-types-and-needle-sensitivity/

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  4. Best Answer

    John D. Collins on Oct 03, 2012


    The scaling is similar between the LNAV, LNAV/VNAV, LP, and LPV for the CDI in that they are all angular for a WAAS GPS. The obstacle protection lateral limits are much wider for the LNAV and LNAV/VNAV in comparison to the LP or LPV, but the CDI scales on a 2 degree wide angular rate for all of them. If the LNAV is flown using a TSO C129a GPS (Non WAAS), then I agree that it does not use angular scaling of the CDI, and is fixed at +/- .3 NM Full Scale Deflection on the final approach segment.

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