Originally Posted by
pilotnik86
The RNP approach cannot be executed with other than GNSS positioning sensor unless specifically authorised by state (which is rare). I haven't seen single pilot who switch off DME/DME, INS and VOR/DME during the approach in order to have pure GNSS-generated ANP.
Have you got a reference for that? AMC 20-27 and 20-28 specifically allow the use of integrated navigation system incorporating a GNSS sensor, provided it is certified, etc.
You might be confusing things with RNP AR, which does not allow reversion to DME/DME, unless the operator is specifically approved. Boeing RNP AR procedures (at least for the 737) require crew to inhibit VOR position updating prior to commencing such approach, with DME updating to be inhibited as well if required.
At least on the 737, there is no way to inhibit IRS position update as such, but its bias is set so low that ANP would skyrocket well before position would drift towards IRS only.