In the Solomons we had a GPS approach for nearly everywhere, but only down to what could be described as a non-precision DA. The GPS kit, as approved by CASA, the Oz CAA, was modified and there were certain checks before you carried out an approach. These included position error and satellite reliability, ie there had to be four satellites in view for all of the projected approach time. The HSI would also indicate full deflection at 1/4 mile error when selected to the GPS approach function.
It used to work. On one approach you were flying directly at a mountain much higher than you and then turning on to the approach track at one mile to go to a CFIT.