Quote Originally Posted by Tatsuo View Post
My FC has the Rank 25 airship, and we cleared sectors 1 through 9, currently otw to 10, and we did not unlock the 2nd airship.
Need to make a correction on my previous post here, I made a mistake, but anyway:

When our ship was rank 25, we had cleared 1 though 8, and it was otw to 8.
It just returned from 5>6>7>8, hit rank 27, and we unlocked the 2nd ship now.

It seems to me that visiting sector 8 does the trick.