I see my mistake, the rules on page 14 are a but unclear, on page 15 (sea bombardement) it is better explained. The rule-book really needs some rework.

If there are no friendly ships under attack, there is no way that you can scramble. The planes are only allowed to support other units and not to start attacks on their own during the attacking players turn. See page 14 in the Rulebook.

Is there any official answer to this? After all New Guinea is an island in real life and i think it should be in the FAQ if this would have changed for the game. For example Australia is specifically mentioned, while nothing is said about New Guinea. What do you think?