In this case, both the Captain and FO had in excess of 4 years and 2,000 hours flying in PNG on Twin Otter aircraft. She would have been formally checked into Kokoda by a Check Captain. In that time (as a guess) they would have both flown the route at least 50-100 times
Word is that the PIC had been checked only recently into Kokoda. Previously been flying LH seat into Popendetta. Had been on the route less than two weeks.