Create GPS Approaches.md

aviation/GPS Approaches.md

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+## Non-Precision (2D Approaches)
+
+Where things like terrain or obstacles prohibit vertical guidance, lateral only approaches can be published:
+
+### LNAV: Lateral Navigation
+
+A traditional GPS approach with lateral guidance only. MDA will typically be as high as 400ft.
+
+### LP: Localiser Performance
+
+The newest type of approach, introduced in 2009. The lateral guidance is angular, with increasing sensitivity closer to the MAP, like a localiser. 
+This differs from traditional LNAV where the sensitivity is constant from the FAF to the MAP. LP therefore gets a lower MDA usually.
+
+## APV: Approach with Vertical Guidance (3D Approaches)
+
+
+#### LPV: Localiser Performance with Vertical Guidance
+
+Require [WAAS/SBAS] capable receivers. Technically still 'non-precision', but can get you down to a low decision altitude, like an ILS, often 200 feet.
+
+
+#### LNAV/VNAV: Lateral Navigation/Vertical Navigation
+
+They were the first GPS approaches with vertical guidance and designed for use with [baro-aided GPS] originally, but can also be used with [WAAS/SBAS] capable recievers these days.
+They are less sensitive than LPV so don't get you as low.
+
+#### LNAV +V: LNAV with 'advisory vertical guidance'
+
+A [WAAS/SBAS] capable receiver can offer advisory guidance on a traditional LNAV only 'step-down' approach. This is not displayed on the chart but the GPS receiever will display it if it is capable.
+The minimum altitidue is still the LNAV MDA.