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4 Answers

NO VNAV on a published LNAV/VNAV approach

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Instrument Rating

Lately I have not been receiving any vertical guidance on a published LNAV/VNAV approach. This approach is the RNAV RWY 12 approach into Norman Manley International in Kingston Jamaica. The annunciator on the GNS430W shows LNAV only. Is this a GNSS problem or is there something going on with my on board equipment? and how do I know in advance if the VNAV won't be available if this is indeed a GNSS problem? Thanks

4 Answers

  1. Mark Babalola on Oct 15, 2012

    I flew in Jamaica for approximately 15 months. There was never vertical guidance at Norman Manley International Airport when you are flying RNAV Approach. If my memory serves me right though, there is a plan to have that capability implement in the near future. When it does come online and serviceable, you will be informed via NOTAM!

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  2. John D. Collins on Oct 15, 2012

    What kind of aircraft and GPS system is installed? I don’t have a copy of the procedure, if you can email one to me at john.collins52@yahoo.com, I can review it. Garmin had an issue with the lateral CDI guidance on LNAV/VNAV procedures that affects some procedures and they did a work around by eliminating the VNAV capability on these approaches. I can look at the approach chart and tell you if that could be the issue.

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  3. John D. Collins on Oct 16, 2012

    The FAA doesn’t post status on LNAV/VNAV with WAAS, but it can be inferred by looking at a combination of the LPV service status and RNP .3 NM service status. The basic LPV and LNAV/VNAV have the same requirement for the vertical guidance (VPL < 50 meters), they only differ in the requirement for lateral guidance. The vertical service requirement almost always determines the area of coverage for WAAS vertical guidance for LPV, LNAV/VNAV, and LNAV+V. RNP 0.3, LNAV/VNAV, and LNAV have the same lateral guidance requirements, HPL<556 meters. See yesterday’s LPV Service area: http://www.nstb.tc.faa.gov/24Hr_WaasLPV.htm and the RNP 0.3 service area http://www.nstb.tc.faa.gov/24Hr_WaasRNP3.htm , and although MKJP is well within the service area for RNP 0.3, it is well outside the area for LPV. Although it is outside the coverage area for WAAS vertical guidance, if the aircraft was equipped with a Baro-VNAV system as are most corporate jets and all the airlines, the LNAV/VNAV could be flown by aircraft so equipped, just not by a WAAS GPS such as the dual 430W that you have installed in your C182P. If you look on your satellite page, you might be able to occasionally get vertical guidance if the displayed value of VFOM (Vertical figure of Merit – 95% confidence vertical accuracy) is less than 60 feet, but I doubt you will find this to be true very often.

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  4. Tromp Effy on May 05, 2013

    I do need the approach plate to enter Manley Airport

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