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7 Answers

Use LNAV/VNAV minimum if LPV minimum is higher?

Asked by: 3271 views , , , ,
FAA Regulations, General Aviation, Instrument Rating

In cases where the LPV minimum is higher than LNAV/VNAV ... would you follow the GPS glide path to the lower minimum? I guess it's illegal, but where's the risk?

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7 Answers



  1. Mark Kolber on Feb 21, 2018

    Whether or not is illegal to begin with is the subject of some controversy.

    The “not legal” folks insist the lowest legal minimums are the ones annunciated on your certified GPS.

    The “legal” group points to FAA guidance saying things like this blurb from the AIM: “Properly certified WAAS receivers will be able to fly to LPV minima and LNAV/VNAV minima, using a WAAS electronic glide path, which eliminates the errors that can be introduced by using Barometric altimetry.” AIM 1-1-8.b.1.

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  2. Alexis von Croy on Feb 21, 2018

    Thank you. Do you see ANY risk in following the LPV to the lower minimum? I could understand that there could be some risk if it was the other way round … but since LPV has the highest precision …

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  3. Best Answer


    John D Collins on Feb 21, 2018

    The LPV and LNAV/VNAV procedures are developed using independent TERPS specifications. The LPV service is annunciated if there is an LPV minimum on the chart and the HPL is lower than 40 meters and the VPL is below 50 meters (35 meters for LPV200). The criteria for the LNAV/VNAV is HPL lower than 556 Meters and VPL is below 50 meters, so any approach which has an annunciation of LPV will meet the criteria for LNAV/VNAV. So if it is safe to fly the LPV, it is safe to fly to the LNAV/VNAV or LNAV minimums, regardless if they are lower than the LPV. It is very common for LNAV minimums to be below LPV minimums, particularly in terms of visibility, yet I have found very few pilots argue that if one has an annunciation of LPV, that they can’t fly the LNAV procedure.

    The safety of using WAAS vertical guidance on an LNAV/VNAV procedure is not disputed and in fact the TSO C146() via RTCA DO-229() allows it for flying the LNAV/VNAV. If the LPV were to be removed from a specific procedure, or, more commonly, added to a procedure that already had an LNAV/VNAV, the LNAV/VNAV procedure would not be modified. So I find it hard to argue that a procedure that was safe, was made unsafe by simply adding a new procedure with tighter requirements and that has no bearing on the LNAV/VNAV procedure. If it was safe to fly before the addition of the LPV, it is still safe to fly after the addition.

    If this were more than an academic issue, there would be guidance available. As it is, the only guidance in the AIM and in AC 90-105A is categorical and does not list conditions. From AC 90-105A, the following is stated:

    A.6.4 LNAV/VNAV Line of Minima Qualification.
    A.6.4.1 Stand-Alone Systems. Stand-alone TSO-C146 Class 2 or 3 systems meet the aircraft qualification requirements for RNP APCH operations using the LNAV/VNAV line of minima provided that the installations meet at least the performance and functional requirements of this AC.

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  4. Alexis von Croy on Feb 21, 2018

    John, as always you deliver the perfect answer! Many pilots I know are interested in this stuff.. and it’s really hard to find the answers!

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  5. Russ Roslewski on Feb 21, 2018

    Do you have an actual example where the LNAV/VNAV DA is lower than the LPV DA? I’d be very interested to see it.

    It’s reasonably common to have LNAV/VNAV that is higher than LNAV due to the different evaluation of the surfaces and DA determination, but I’ve never seen LNAV/VNAV be lower than LPV.

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  6. Mark Kolber on Feb 21, 2018

    Sure. Look at the GPS 21 into KTTA.(Link to current chary: http://155.178.201.160/d-tpp/1802/09472R21.PDF)

    It’s my home airport (which is how I first got into the topic) The LPV minimum is 530; the LNAV/VNAV is 50 feet lower.

    BTW, I agree completely with John. But I know of folks with equal credentials who don’t. And, in terms of a checkride or IPC, all bets are off. You will find both viewpoints.

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  7. Alexis von Croy on Feb 21, 2018

    My exampe is the EDTD airport in Southern Germany (Donaueschingen). The LNAV/VNAV DA is 2589 ft while the LPV’s DA is 2789 … so it’s 200 ft higher. LNAV is 2790 ft (and what’s strange is that the LNAV minimum is DA(H) – not an MDA!

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