the wrong reference point for the distance, using the NDB ( GPS distance from the NDB )instead of the ILS DME, the descent was premature.
Understand the distance measuring from the beacon instead of the ILS was the issue, but putting the distance thing aside, are they saying that in addition to flying to the beacon IAP (which is the correct procedure) he used the beacon for lateral guidance inbound also, so not only was he not using the Dme, he never had the Procedure loaded on the 530 or even tuned the ILS in on a nav radio with CDI (separate from the 530) essentially flying an ad hoc NDB approach using the published localiser approach step downs for GS guidance.
Essentially none of the components for the requested ILS DME 09 approach (localiser, glide slope , Dme) were used by the pilot to fly the approach ?