Australia 1938,  the Australian Territory of Papua and New Guinea,  was a weekly service in each direction, taking two and a half days between Sydney-Rabaul. W.R. Carpenter Airlines “CARMANIA” VH-UYU left Australia May 30 with first flights to these exotic places, for which 5d in stamps had to be added to each cover – 2d for postage and 3d for airmail fee. And THEN these covers were “Boomeranged” back from both New Guinea and Papua and same rate – 5d in those stamps were added.
Relevant backstamps on all 3.