If say the Willy RAAF base had long ago been shifted from its rather vulnerable coastal position, to somewhere up closer to our threats say Tindal (where miltary airspace abounds,) and if MDX had therefore been permitted to flight plan coastal the aircraft would not have been in a position where the pilot's purported limited abilities were insufficent. Therefore the accident would most likely not have happened. I am not sure what a "primary cause" is. Any break in the chain, no matter how trivial, can oft times avoid an accident.