@Paxboy
Some info on the Iran crash
here. Quote from The Scientific-Technical Commission of the CIS Interstate Aviation Committee (MAK) report as reported on web-site flightglobal.com
[MAK] says the crew made a number of errors, including:
* failure to apply approach procedures;
* incorrect reliance on the GPS, in breach of its operational requirements and their rating for its use on approach;
* failure to use information from other installed navigation equipment;
* failure to seek an alternative approach when they realised the GPS could not be giving a realistic DME readout.