MJ
You are describing a procedure in your company manual, presumably approved by the CAA under your company's AOC. What you describe is unsuprising, for a public transport AOC manual.
I don't know anything about AOC manuals but I heard from a pilot on one of the low cost airlines, flying an NDB approach, flies it using the INS but they are supposed to check they are within 5 degrees on the RMI (ADF) before descending from the FAF; they are allowed to ignore the NDB after that, until the MDA. This is just another example of a CAA approved procedure (B737) which differs hugely from standard IR training.
There must be loads of these manuals around, with different procedures for different things. Like the USAF one mentioned earlier.
But we are not talking about AOC ops here and CAA approved manuals. The context is private flying, around Europe, and the safest way to navigate.
What others have written, here and elsewhere, is that usage of GPS is variously illegal or unauthorised, and similar legal-looking statements. Every one of those statements is complete b0ll0cks. Even if some look like they come from somebody employed by the CAA.
Less complete b0ll0cks would be a statement that GPS can fail. Of course it can fail, anything can. So anybody with a brain will fly GPS/VOR/DME. Did I ever say anything to the contrary?
The GPS bit will be working perhaps 99.9% of the time; I've had about 2 minutes of non-function in 500 hours which is 99.994% (KLN94). The VOR will be receivable anywhere from say 50% of the time (UK-style VFR or IFR, especially OCAS, or in many places abroad, all depending on how much you like to compromise the route to lie on VORs) to say 90% (ATS routes in low level airways), but on airways flights you will often get a DCT to a VOR which is way outside its DOC - as you presumably must know, looking at your job. Unless you refuse any nice long DCT legs offered by ATC. Maybe you do, so you are always within the DOC of something. Otherwise, much of the time, a BRNAV GPS (or an INS but that's irrelevant to GA) is the only thing that will give you the track guidance to the waypoint given. As for DME, similar comments as for VORs and in addition there are swathes of France where the only DMEs are the low power ones on ILS airports. Surely I am teaching you to suck eggs here!
You mention Selective Availability. At most, SA introduced an error of hundreds of metres. Irrelevant for en-route aviation. Much more of a problem running TomTom in the car though
SA was removed over 10 years ago. It was removed not because the mil sets were expensive; that's complete nonsense, but because the military have in-theatre jamming capability coupled with their own anti-jam receiver technologies (e.g. combining a FOG with a GPS and special antennae; very cheap with so many smart bombs carrying the stuff).
GPS is far and away the most reliable nav device available to man, with the added bonus that its failure is generally very obvious.
There has to be a limit to how much time somebody on here will spend repeating the same old obvious statements.