Stand Alone GPS Approaches
These are non-precision approaches designed based in sole use of GPS equipment. These approaches are slowly being phased out and at present less than 200 approaches are left world wide. Approach charts for stand alone GPS approaches are marked as “GPS RWY” example : GPS RWY 16, GPS RWY 32.
GPS Overlay Approaches
This was temporary method (GPS overlay program) adopted to allow the use of IFR approved GPS receiver for non-precision approaches. This program was terminated in 2009. GPS Overlay Approach charts for GPS Overlay approaches were marked as “VOR or GPS” OR “NDB or GPS”.
With the development of PBN, GPS overlay approach procedures have been reworked on. They are now defined with respect to RNAV system. Current circulars are marked as “Use of Suitable Area Navigation(RNAV) Systems on Conventional Procedures and Routes”.