When entering with an FC owned airship, players outside of the FC may also be invited. However, this will require having two members from the FC who own the airship to be in that party.
This requirement for TWO FC members is a big problem! >_<
It will be common to have a group of friends who want to do a hard-mode island expedition but the players with airships don't have another FC member who wants to come (late at night, others busy, solo fc, whatever). This restriction means they will be stuck sitting around unable play, begging people who don't want to come. And they will be forced to kick out somebody who did want to come to make room.
Requiring two people from the same FC doesn't make the game more fun for players. It just locks out small FCs and groups of friends in different FCs from significant content! Please please reconsider. >_<