If you haven't gone ]been already Airlines as stated by seahorseeker are very slow in general they work on island time, their attitude is don't worry well get you there, time doesn't mean much to PNG folk I'm afraid, they are not clock driven as we westerners are.
Plane safety is high as they fly into some really hairy airstrips in the mountains of PNG, weather permitting. PNG pilots are generally Australian or trained in Australia. In saying this all of the coastal strips I have landed on are large and well maintained.
No issues with the planes. Agreed with Seahorse that planes may or may not arrive on time or even at all. This is either the airline policy or flight schedulers issues.