CoastalDriver wrote on Dec 21^st, 2011 at 10:44am:

Oh and I forgot, Doppler is a long range nav system only and you would always track via the primary aids for the airport concerned once you came into range of the relevant VOR or NDB. All ground based aids are regularly tested for accuracy and reliability and hence have fine tolerances, but airborne equipment like Doppler and INS is not considered accurate enough for precision and non precision approach work and hence you will never see a Doppler or INS instrument approach but modern GPS systems are different and are accurate and reliable enough to be used for precise instrument approaches. Doppler and INS were fine over the ocean or long distance as ATC kept you a couple of thousand feet apart from aircraft above and below you and at least laterally by about 5 to 10 mins depending on the sector length. So you can see with that volume of airspace around you as a buffer off track errors could be tolerated (well up to a point). All professional pilots pride themselves on the accuracy of their navigation so your thinking about it and working on keeping on track and level at all times.

When I use my CIVA INS it allows me to enter VOR station data for position updating and increased accuracy. I though this type of technology fed right into the core of modern FMS equipment.

Oh well, I still plug all the lat long co-ords on a STAR chart into my INS when I need RNAV in the 727.