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Which approach is which?

The proliferation of RNAV approach procedures and associated standards based on GPS, WAAS-enabled GPS and barometric sensing come with different equipment requirements and performance capabilities. Here are the four most-common RNAV approach procedure types, along with their definitions, equipment requirements and limitations:

LATERAL NAVIGATION (LNAV)

An RNAV function that computes, displays, and provides horizontal approach navigation without approved vertical guidance.

LATERAL NAVIGATION/VERTICAL NAVIGATION (LNAV/VNAV)

An RNAV function that computes, displays, and provides both horizontal and approved vertical approach navigation. Both WAAS vertical guidance and baro-VNAV support approaches to LNAVNNAV lines of minima.

LOCALIZER PERFORMANCE WITH VERTICAL GUIDANCE (LPV)

An RNAV function requiring WAAS, using a final approach segment (FAS) data block, which computes, displays and provides both horizontal and approved vertical approach navigation to minimums as low as 200-foot ceiling and 1/2-mile visibility.

LOCALIZER PERFORMANCE WITHOUT VERTICAL GUIDANCE (LP)

An RNAV function requiring WAAS, using a final approach segment (FAS) data block that computes, displays and provides horizontal approach navigation using the horizontal accuracy and integrity of LPV without the approved vertical guidance. The LP line of minima is provided at locations where issues prevent the use of LPV vertical guidance, and provides a higher probability of achieving the lowest minimum at these locations.

Every IFR-certified and installed GPS unit allows the pilot to descend to LNAV (i.e., straight-in) and circling MDAs. Baro-VNAV-equipped GPS systems can also descend to LNAVNNAV minima. Meanwhile, WAAS-enabled GPS navigators can be used to descend to LNAV, LNAVNNAV and LPV minima.

Another way to keep it all straight is to look for the decision altitude (DA) designation versus the minimum descent altitude (MDA) abbreviation on the approach plate's minima line. Only procedures with vertical guidance have DAs. A descent angle may be provided on procedures which have only LNAV minima, to aid in a stabilized descent, but the MDA must still be respected.


RNAV Approach Type And Vertical Guidance

Approach Standard  Approved vertical  Advisory Vertical
                      Guidance               Guidance
LPV                    Yes                    No
LP                     No                     Yes
LNAV/VNAV              Yes                    No
LNAV                   No                     Yes
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Title Annotation:INSTRUMENT FLIGHT
Publication:Aviation Safety
Geographic Code:1USA
Date:Oct 1, 2014
Words:339
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