Typically the following sources of information are used by the FMS to establish the aircrafts position:
VOR/DME, ADF, LORAN C, Radio altimeter.
VOR/DME, ILS, IRS, GNSS, Radio altimeter.
Map reading Weather radar, ILS, IRS, GNSS, Radio altimeter.
VOR/DME, ILS, ADF, GNSS, Radio altimeter.