Originally Posted by
RG1979
It's actually a level D sim I'm talking about ;)
With a multi-sensor system and display, you're not so much concerned about the source of the data as what you're given. Many units combine VOR information, DME, DME-DME, GPS, IRS/INS, etc; it only outputs nav data. You can delve into the system to explore sensors and sensor availability, but unless the system advises you that the input isn't available or is questionable, all you really care about is whether you have nav guidance.
You may be on an approach with a marker or NDB or DME inoperative, yet your system provides GPS data which replaces the missing elements and gives you what you need to fly the approach. So long as the required navigation performance is available, the particular source of the data becomes ancillary so long as it's valid data.