bubbers44:
We didn't get GPS until my last couple of years before retirement but losing systems on that base leg with mountains on both sides would be very interesting. I now stand corrected and the RNAV 02 from the north would have prevented this accident. I still can't believe they approved this approach to those low minimums with mountains all around them and that close. Can you skin that close to mountains on an ILS? I didn't think so but never having done a GPS RNAV approach have no knowledge of the rules so I will shut up.
This is not an ordinary GPS approach. It is an RNP Authorization Required approach. (RNP AR). Whenever an RNP AR approach requires less than RNP 0.30 or the missed approach requires RNP of less than 1.0, then the position has to be backed up by at least one IRU for additional FMS position. Thus, if the GPS fails, the IRU or IRUs (usually three) will provide sufficient position accuracy to complete the missed approach procedure.