Airbus FLS Monitoring VOR/NDB Raw Data

[CrazyStuntPilot]

The MMR uses GPS data to compute aircraft position for the FLS approach with F-APP capability, which is why there is no need to monitor the navaids.

With a number of failures however, e.g., GPS Primary Lost or NAV/FM Pos Disagree, the position may be correct but susceptible to errors, so you must monitor the navaids as the FLS capability degrades to F-APP+RAW to check your position during the approach and should not rely on the distance shown on the PFD from the FLS anchor point for the dist/alt check but instead use the DME data on the ND.