Guys you are all barking up the wrong tree with your armchair analysis.
Firstly my heartfelt condolences to SB's family, DB and all the members of Christian Aviation, I had many dealings with them and they were probably NZs best GA charter operator.
As for your arguments about SPIFR, I could almost guarantee that was not the problem in this case. Some of you have made the comment "stick on the right track keep to your minima’s and you will never hit terrain", I agree in principle but you have never flown that particular approach. I have flown it many times (almost daily for a 3 year period) at it can be pretty scary.
The "AP" NDB suffers serious coastal effect from the lake that drags you towards Mt Te Aroha, what is worse and prob the case in this accident is when the "turn in" off the DME ARC is not indicated till well through the inbound track. CAA had been advised a few years ago about the inaccuracies of this approach but at the cost of putting a VOR or 2nd NDB in decided to do nothing. Be it a Senica or a Bandit or a Metro all would (could) be led into this trap.
A very tragic loss.