Yeah I fully understand that, my original question was why MSFS was doing this while the GPS had no knowledge about the actual RNAV approach at all (no procedure selected).
Thanks for clarifying that. All makes sense now and I learned something!
If you want to play with RNAV glideslopes, try West Yellowstone KWYS RNAV 19 approach. It is about 14.5 miles long. There is no ILS on that runway, so the glideslope info is coming from the GPS.
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let PFD in FMS=GPS, no frequency is needed, follow all the altitude from a chart about 10 to 20 miles from landing descent to the last altitude on the chart, the diamond will go up to the center, then will land by itself just like a ILS.
MSFS ATR RNAV Approach
First of all, when you creating your FMS Flightplan you must select a suitable RNAV Approach for your Destination Airport.
In the according charts you will find the MDA barometric height for your approach.
Turn the DH/MDA switch to MDA and set the Altitude to 400. Its important to set MDA on both sides, Pilot and CoPilot, otherwise MDA will keep flashing.
Now depart and climb to cruise Altitude and relax until ToD. Short before reaching ToD, set the Altitude to 2000, which is the FAF for the example above.
Wait for the vertical path to be calculated by the FMS , then you can see the Magenta indicator on the PFD.
Now you are able to pressVNAV button. Without vertical path calculated and indicated by the FMS, VNAV will not work. If the waypoint for FAF has an height assigned in the FMS, this will be shown in Magenta above the VNAV Indicator. Magenta means always, calculated by the FMS, blue means input from Pilots.
The PFD wil now show
Waiting for the chime, indicating that you reach the altitude of FAF.
Now dial in the MDA Altitude and press APP in FMS Mode (not V/ILS).
V-FP will NOT engage as long as you follow a VPATH (dont know if this a bug or a Feature 
The PFD wil now show
As the ATR has no Autoland, when reaching MDA and the Runway is visible and clear of obstacles, disarm the autopilot and land.
Hope this brief description helps for successfull landings.
Chris
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Since the forum was restructured recently, this was moved to #gd-commsupport:anc
Unless I’m completely mistaken I think you have something mixed up here - I believe the table you are showing has nothing to do with DH / MDA. This is the descent/timing conversion table which shows the corresponding descent rate for the given GP angle and air speed. In your example you would need a descent rate of 531 ft/min to follow the 3 degree glide path when flying 100 kts…
The DA/MDA is shown here:
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Thanks for the hint Woodstock … you’re right 
. It’s for sure the descent Rate for 100 knots what i’ve marked. I’ve corrected my post, not to mislead someone 
Chris
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Thanks for pointing this out. Even in late 2023, this issue is still present.
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