Default GPS Approaches

[pgde 571]

Hi All: In the default GPS, what is the difference between a GPS approach and RNAV approach? Actually, I was wondering this in the FSX days also.

Happy Thanksgiving!

P.

[snpower 16]

As you are probably aware, RNAV refers to point-to-point navigation. In the US, RNAV has become more or less synonymous with GPS. There are several types of GPS based approaches utilized when the instrument approach procedures for a particular runway are labeled ‘RNAV’. These are LNAV, LNAV/VNAV, and LPV. 

LNAV provides localizer type lateral guidance and uses an MDA. Accuracy does not increase the closer you get to the runway, so higher minima is required.

LNAV/VNAV is like LNAV except GPS provides altitude information so minimums should be lower.

LPV provides ILS precision based on GPS position and WAAS altitude data. Accuracy increases as you approach the runway; this is the “best choice” for IFR operations, when available and your bird is properly equipped.

[WarpD 824]

More importantly... GPS approaches are legacy approaches designed by the FAA when GPS was still fairly new. They use fixed minima based on controlling obstacles like traditional radionavigation approaches. ... The RNAV (GPS) approaches were then born, which contained minima based on differing levels of GPS precision (LNAV, LNAV/VNAV, LPV).