RNAV LP Approaches removed from GNS and GTN Databases

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  • #84642

    I read this on Beechtalk. Apparently, if the VDA on an LP approach has obstacle clearance issues…below MDA, the entire approach and it sounds like even the underlying dive-n-drive approach are both removed from the database. No NOTAM, no warning. You’ll find it when you push your PROC button. Well thought out. 😐

    quote :

    I raised this issue with the ACF/IPG. IMHO, the issue is with bad decisions that AeroNav made on incorrect assumptions. When an approach is flight tested now a days, a check is made by flight test to determine if there are obstacles on the advisory glidepath when below the MDA and in the visual segment that represent a threat if the VDA is followed. The VDA is the angle that ends up being used for the advisory vertical guidance. Advisory vertical guidance was never intended to be usable below the MDA. When the obstacle situation occurs, flight test reports it and the result is that the VDA is removed from the approach chart and a note is added to the chart “Descent angle NA”. This was added to the chart because some FMS systems will calculate a VDA on all approaches regardless if the angle is supplied or not. The note is intended to prohibit the use a self calculated VDA for advisory vertical guidance, meaning that if an advisory GS is displayed, by this note, the pilot is not to use it. In the case of the existing Garmin LP software, there is no advisory vertical guidance provided, so it should not be an issue. However, some smart person in AeroNav decided that if they coded the angle to zero in the database that it might make any equipment not use the advisory glidepath. This had the unintended consequence to not be coded in the database and the result was that the LP lower minimums were lost. The FAA is in effect forcing that all procedures must be able to be flown with a constant angle descent and that there is no place for a dive and drive technique. I estimate that this may eventually result in the loss of up to several thousand approaches to the backwater airports that currently only have LNAV minimums as they get flight tested. Note that the angle is the same for an LP or an LNAV and since an LP is only charted when the approach is not suitable for use with a GS (or an LPV would have been charted in the first place!). Is it really a surprise when an approach not suited for vertical guidance is found to also have obstacles that don’t permit the use of an advisory glidepath below the MDA, DUH. The VDA does not need to be coded as a zero, all that needs to be done is that the vendor be made aware that a VDA should not be used to provide for advisory vertical guidance. In the future, Garmin and other vendors may add advisory vertical guidance to LP procedures (aka LP+V), but many will not be possible because of the challenging locations of obstacles, and the only realistic way of flying these procedures is with our Category A and B type aircraft using the dive and drive. The alternative is to eliminate these approaches, and I strongly disagree with this approach. There are times and circumstances where the dive and drive technique is appropriate.

    _________________
    Regards,

    John D. Collins CFI, CFII, MEI
    68 V35A N7083N Home Base KUZA
    Charlotte, NC
    (704) 576-3561 Cell

    #101972

    That’s not good, especially for people like me who use those LPV approaches to small backwoods airports. That was the whole point of LPV approaches, wasn’t it?

    #101976

    Ted,

    I am still trying to wrap my head around this. But, I don’t think LPV approaches are affected. It looks like LP approaches with an advisory VDA and possibly the underlying non-precision approach are being removed from the database.

    #101980

    Tom,

    That would make more sense. It would still annoy me, since my current field is an LNAV only approach. WAAS gives me a glide path. MAP to runway glidepath is obstacle clear, but may not be high enough above to count from the FAA. That might be enough to convince me to move airports. I like the glide path on night approaches as an extra help, and having flown it in day VFR I know what clearance it gives me. This would be removing an extra layer of safety.

    I do understand their point that some people will just blindly follow the vertical guide, without understanding that what it means. That’s what they are probably trying to avoid.

    #101984
    quote TDUPUIS:

    That might be enough to convince me to move airports.

    I wish I had your problems. πŸ™‚ I can’t swap airports unless I want my already 28 mile, 35-ish minute (minimum, no traffic) drive to the airport to jump up to at least an hour!

    I’d trade my 600 & 2 1/2 minimums LNAV-only approach with a 90ΒΊ turn at MAP for a 200 & 1/2 LPV or 200 & 1800RVR Cat II any day… If I could. πŸ™‚

    Cheers,

    Doug

    #102017

    Doug,

    I spent 20 years in New York City, so I feel your pain. Spent time in both the private and public school systems, fixed Jaguars on Long Island, etc. All I can give for advice is:

    Leave! Life is better elsewhere. πŸ˜€

    Keep in mind I’m also flying out of a 2800 ft airport. Linden is a good bit longer. Although having shot your approach to mins and gone missed (and had approach tell me “Going missed is not an option”), I do not envy your approach. πŸ˜‰

    By the way, I enjoyed your article in this month’s issue. It’s nice to see others doing long family trips in their 310s that work out as great successes, and what I’m hoping for as our son grows (and perhaps a sibling for him). Sometimes it can be hard to see the future past the dirty diapers and needing to stuff the 310 to the gills for an overnight.

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