DozyWannabe,
The changed co-ordinates that Mahon thought so important are to my way of thinking irrelevant as to the cause of the accident.
The mandatory descent requirements stated that 16,000ft be maintained until overhead TACAN29, and then commence .the approved let down.
No where it would appear is there any approval for a VMC descent prior to reaching the TACAN.
Other flights apparently commenced descent earlier, but they had all been identified by radar and were in CAVOK weather conditions.
If one wishes to disregard the rules one must make sure your reasons are fireproof.
In this case they were not, the obvious proof is the end result.