Adventurer Fiction series with Papua New Guniea and Time Travelling Dinosaur Hunting. Read early 2000s. Spoilers.

[Mithra]

I read first two entries of this series in early 2000s, from the looks of the books (they were 2nd hand) they should be more older.

IIRC, first book our main character is a pilot or ex-soldier near New Zealand / Papua New Guniea. They were tasked with carrying a millioniare from somewhere but they are shot down. Maybe they were going to a hunting? Our MC, finds the millioniare now is hostaged to a tribe that will sacrifice the millioniare. He saves him, they reach back to a plane and escape safely. There maybe others in the group, I hazily remember some characters but I am not sure. Possible some scientist, maybe a women (love interest of millioniare) and others not sure. I also remember this tribe's village were inside of a mountain or something.

FYI, I referred the character as millioniare because of 2nd book, I think he was millionaire at first book as well but not sure.

Second book, years later wife of the millioniare reaches out to MC saying he can't reach out to millioniare for some time. MC investigates finds out rich character have been funding a researcher. That researcher finds a way to travel back in time. MC follows them to Mesozoic era. Turns out a few rich people funded this researcher to travel back in time to hunt dinosaurs. However, they get greedy separated, hurt, and one team member uses machine prematurely and come back to current time (hence our MC can travel back in time) so they are stuck in that time. MC finds them, and later on they reach back to time machine and come back safely.

I think these were the order of books, but they may be reversed.