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2 Answers

LPV CDI sensitivity

Asked by: 5653 views FAA Regulations, Instrument Rating

The CDI sensitivity for WAAS capability aircraft is 

enroute +/- 2nm

termianl +/- 1nm

approach +/- .3nm

is the CDI sensitivity the same for a LPV approach. I was told that the sensitivity of the CDI goes up too +/- .1nm but I can't find a source that says this exactly. So if you are able to provide a source and to verify that .1nm is correct for a LPV approach. 

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2 Answers



  1. Russ Roslewski on Aug 27, 2016

    I think AIM 1-1-19(d) should be able to answer you questions, and provide a lot more information that you may want. (Since you’re asking a pretty detailed question, I suspect you may also be interested in a higher level of detail than is typically taught.)

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  2. John D Collins on Aug 28, 2016

    The LPV CDI FSD (Full Scale Deflection) is 1 NM until reaching a point 2 NM prior to the FAF. The FSD then transitions to the value for the FAF to threshold. At the FAF, this is equivalent to +/- 2 degrees measured from a calculated point beyond the threshold such that when at the threshold, the FSD is +/- 350 feet. It continues at a fixed value of +/- 350 feet until reaching a reference point (about 1000 feet from the threshold) and after that, is changes to a fixed value of +/- 0.3 NM.

    So as a practical matter, it is similar to an ILS with a runway length of about 10000 feet. It is angular for the final approach course (+/- 2 degrees) and not a fixed value. It is +/- 350 feet at the threshold and continues at this value for another 1000 feet before increasing back to 0.3 NM.

    My reference for this is from RTCA DO229D, which is the technical specification for a TSO C145/146 WAAS GPS Navigator. You have to be a member of RTCA to get this document for free or must pay $370 for a copy.

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