Good question Alex and what I was sort of alluding to a few posts back. Without the plate you can’t cross check waypoint sequencing and height restrictions so it doesn’t seem unreasonable not to fly the RNP approach. The investigation states that DME not available, so the NDB Z not available, which only leaves the NDB Y.
There’s no reason why LNAV couldn’t be used (backed up by raw data and taken over by Hdg Sel if required) but the error was the early descent below platform.
The big save was response to the GPWS warning. We’re doing EGPWS in our current sim sequence and a big discussion area is ‘can you imagine how difficult it would be to have to ditch the SA you thought you had and carry out the manoeuvre? And then to have to rebuild that SA prior to having another go. And then to have to prep and fly the return flight knowing that there will be awkward conversations to come.’