It is common practice in the RAAF for the person who is qualified to operate the larger aircraft in the fleet to be referred to as Captain. What it means is that he or she is able to fully able to operate the airplane and where required to supervise the crew.
It has nothing to do with rank, though often that person would be referred to as captain and the other members of the crew by their position.
When I joined the RAAF NCO crews or part there of where common. One would find a SGT pilot referred to as Captain.
I guess referring to a a person as Captain clearly indicated who is in charge and has nothing to do with his real rank. I have flown with lots of FLT/LT navs but they were always referred to by their rank or crew position.
We are also having demonstrated what a capable aircraft the AP3C is and airplane which is getting over 50 years old is still proving to be very capable.
As for the maintainers second to none the aircraft look almost brand new.
Regards
Col