Yeah, I am still searching for the reason why PRNAV is "needed" for its lateral accuracy. For example, these four track fragments, which I captured with my ancient kit
are all within 0.5nm of the track, except the last where the overshoot (I did that one with turn anticipation disabled in the GPS) is 1nm i.e. within PRNAV limits.
This is a more typical arrival sector performance
Yet, for me to get PRNAV approval I would have to rip out all this perfectly working kit and put in other kit which won't deliver anything different to the controller.
It should be readily apparent that PRNAV is something devised back in the great days when a Tupolev from the Peoples Republic of Upper Volta could land with 1 engine out at LHR and depart as it came
But where there is money, there is a gravy train running on it, and there is no shortage of people trying to jump on it. The avionics installers love this. How much does it cost to upgrade some regional turboprop to this "capability"?
And there is a lot of certification work involved in this, which keeps the nice people at EASA at work. What goes around comes around