I read this somewhere, but I am not sure if (a) it’s true and (b) it has some caveats.
Would be strange wouldn’t it? it is a complete different system. A non WAAS GPS would also do much better then 4 degrees which is allowed for VOR.
A VOR check is needed if you use a VOR for navigation per FAR91.171. Peter the PPL/IR discussion where I assume you saw this describes it well.
91.205 requires that the aircraft be equipped with navigation equipment suitable for the route to be flown under IFR. In the US, an aircraft may fly IFR without any VOR on board if it is equipped with a WAAS GPS as a TSO C145/146 GPS may be used for sole source for IFR navigation. As long as one does not use the VOR on an IFR flight, 91.171 doesn’t apply. The VOR check does not apply to a localizer course, so an ILS may be flown without the need to comply with 91.171. In the US, a GPS may substitute for a VOR, ADF, or DME. The only requirement for VOR IFR navigation in the US is when flying a VOR approach, between the FAF and MAP. Other than practice approaches, I have had no need to fly a VOR approach in the US going on 8 years. Same is true for an ILS or ADF approach. So for me, doing a VOR check is not necessary, but I still do it because it takes less than a minute during a flight to make a record to record the comparison between two VOR indications.
where I assume you saw this
Never assume, Jason. One day it will bite you when you are flying your plane and you might end up in a compromised obstacle clearance situation 
FYI I have been flying N-reg since 2005, had the FAA IR since 2006, the FAA CPL since 2008, and read some US forums where this stuff comes up regularly.
As long as one does not use the VOR on an IFR flight, 91.171 doesn’t apply
But only if you have a 145/146 GPS – correct? With a KLN94 or a GNS430/530 one still has to do the 30 day VOR checks for any IFR flying, enroute or approaches, I think.
But only if you have a 145/146 GPS – correct? With a KLN94 or a GNS430/530 one still has to do the 30 day VOR checks for any IFR flying, enroute or approaches, I think.
Correct. For non 145/146 GPS systems, they are only approved for supplemental means of navigation and do not meet the 91.205 requirement.
