One of the things I see often on IFR stage checks and IPCs is a lack of familiarity with the different kinds of GPS approaches and their respective capabilities and idiosyncrasies. Introduction of Localizer Precision (LP) approaches has made that worse. Given that the U.S. has over 12,000 GPS approaches, it’s time we mastered the variables.
GPS Alphabet Soup
Key Takeaways:
- The article differentiates five GPS approach types: non-precision (LNAV, LNAV+V, LP, using MDAs) and precision (LNAV/VNAV, LPV, using DAs), with Wide Area Augmentation Service (WAAS) critical for improved accuracy and lower minimums in most.
- LNAV approaches are basic and non-WAAS. LNAV+V introduces a mathematically derived advisory glidepath that, despite visual guidance, remains non-precision and may not guarantee obstacle clearance below the Minimum Descent Altitude (MDA).
- Precision approaches like LNAV/VNAV offer WAAS-enhanced vertical guidance. LPV is the most precise, delivering ILS-like angular guidance and accuracy, allowing descents to very low Decision Altitudes (DAs) and functioning as a ground-equipment-free Category I approach.
- LP (Localizer Performance) is a newer non-precision WAAS approach providing enhanced lateral guidance with increasing sensitivity, designed for locations where terrain prevents vertically-guided LPV procedures and offering lower MDAs than LNAV.
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