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LPV vs LNAV/VNAV

Discussion in 'CFI Corner' started by GreenDayPilot, Jan 20, 2010.

  1. GreenDayPilot

    GreenDayPilot Well-Known Member

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    What is the difference between LPV and LNAV/VNAV? The minimums are usually higher for LNAV/VNAV, but why? What are the specs?

    Thanks!
     
  2. Pilot Hopeful

    Pilot Hopeful Well-Known Member

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    AIM 1-1-20. Wide Area Augmentation System (WAAS)

    b. Instrument Approach Capabilities

    1. These new procedures called Approach with Vertical Guidance (APV) include approaches such as the LNAV/VNAV procedures presently being flown with barometric vertical navigation (Baro-VNAV). These approaches provide vertical guidance, but do not meet the more stringent standards of a precision approach. Properly certified WAAS receivers will be able to fly these LNAV/VNAV procedures using a WAAS electronic glide path, which eliminates the errors that can be introduced by using Barometric altimetery.

    2. A new type of APV approach procedure, in addition to LNAV/VNAV, is being implemented to take advantage of the high accuracy guidance and increased integrity provided by WAAS. This WAAS generated angular guidance allows the use of the same TERPS approach criteria used for ILS approaches. The resulting approach procedure minima, titled LPV (localizer performance with vertical guidance), may have a decision altitude as low as 200 feet height above touchdown with visibility minimums as low as 1/2 mile, when the terrain and airport infrastructure support the lowest minima. LPV minima is published on the RNAV (GPS) approach charts (see paragraph 5-4-5, Instrument Approach Procedure Charts).


    d. Flying Procedures with WAAS

    1. WAAS receivers support all basic GPS approach functions and provide additional capabilities. One of the major improvements is the ability to generate glide path guidance, independent of ground equipment or barometric aiding. This eliminates several problems such as hot and cold temperature effects, incorrect altimeter setting or lack of a local altimeter source. It also allows approach procedures to be built without the cost of installing ground stations at each airport or runway. Some approach certified receivers may only generate a glide path with performance similar to Baro-VNAV and are only approved to fly the LNAV/VNAV line of minima on the RNAV (GPS) approach charts. Receivers with additional capability (including faster update rates and smaller integrity limits) are approved to fly the LPV line of minima. The lateral integrity changes dramatically from the 0.3 NM (556 meter) limit for GPS, LNAV and LNAV/VNAV approach mode, to 40 meters for LPV. It also provides vertical integrity monitoring, which bounds the vertical error to 50 meters for LNAV/VNAV and LPVs with minima of 250' or above, and bounds the vertical error to 35 meters for LPVs with minima below 250'.


    5-4-5. Instrument Approach Procedure Charts

    k. Area Navigation (RNAV) Instrument Approach Charts.

    1. The minima lines are:

    (b) LPV. "LPV" is the acronym for localizer performance with vertical guidance. LPV identifies WAAS APV approach minimums with electronic lateral and vertical guidance. The lateral guidance is equivalent to localizer and the protected area for LPV procedures is now the same as for an ILS. The obstacle clearance area is considerably smaller than the LNAV/VNAV protection, allowing lower minima in many cases. Aircraft can fly this minima line with a statement in the Aircraft Flight Manual that the installed equipment supports LPV approaches.

    (c) LNAV/VNAV. LNAV/VNAV identifies APV minimums developed to accommodate an RNAV IAP with vertical guidance, usually provided by approach certified Baro-VNAV, but with lateral and vertical integrity limits larger than a precision approach or LPV. LNAV stands for Lateral Navigation; VNAV stands for Vertical Navigation. This minima line can be flown by aircraft with a statement in the Aircraft Flight Manual that the installed equipment supports GPS approaches and has an approach-approved barometric VNAV, or if the aircraft has been demonstrated to support LNAV/VNAV approaches. Aircraft using LNAV/VNAV minimums will descend to landing via an internally generated descent path based on satellite or other approach approved VNAV systems. Since electronic vertical guidance is provided, the minima will be published as a DA. Other navigation systems may be specifically authorized to use this line of minima, see Section A, Terms/Landing Minima Data, of the U.S. Terminal Procedures books.
     
  3. GreenDayPilot

    GreenDayPilot Well-Known Member

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  4. Roger, Roger

    Roger, Roger Guest

    LPV requires WAAS.

    LNAV/VNAV can be flown with either WAAS or an approved baro-aiding system.
     
  5. CFI4life

    CFI4life New Member

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    Localizer Performance with Vertical guidance. The course tapers down the closer you get to the runway/MAP. Thus....you get to go lower. The GS is the "same" on LNAV/VNAV however the LNAV/VNAV approaches only go as accurate as .3 miles on either side of the course. (you don't want to be over a quarter of a mile off course 200 feet off the ground.)

    The LPV, I believe goes to .1 or maybe even .05.....Also you'll see RNP .3 required on certain RNAV approaches which is a Required Navigational Performance which is the tolerance of .3 either side of the course. This is for the old school RNAV and some FMC/S.
     

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