In the latest update these issues are supposed to be fixed. The original posters sale to someone else causing planes to be lost is likely still in effect. I will leave this thread here, but it should be irrelevant now.added by VorlonFCW 1-23-18
Simple rule for carriers: NEVER Merge/Split/Sell a carrier group with planes on the Deck. Just don't.
Perhaps Carriers should come with a warning label because of the way they work. Of course very few players would read the instructions anyway. . .
If a carrier is destroyed the planes are destroyed as well, because it is silly for a carrier to sink and the planes turn into convoy ships where the carrier was.
So the way that planes find out if their carrier is destroyed is by checking for the "uni designation" of the carrier. For example if my carrier group is AB12 the planes are linked to that designation AB12. If AB12 vanishes the planes assume that their next stop is the bottom of the ocean.
I am sure you have noticed that when you merge units together they become identified by one stack number. So if you merge carrier AB12 with a big fleet called AB11, you will likely have the whole fleet called AB11, and the planes assume AB12 was destroyed, so they sink.
Same with splitting up a fleet. If you have carrier group AB12 and you split it in half one part still would be called AB12, and the other part would be the lowest available number, perhaps AB21. If the carriers were in the part now called AB21 - planes again sink.
I am sure you can make the connection from the above examples about selling a carrier group and the resultant name change. I make no guarantees about the solution below working correctly in the case of selling carriers, as I have not tried it.
So the Solution is to have the planes on Patrol at the least. Planes on patrol will hunt for a new airbase or carrier within range and try to attach to it, rather than simply fall from the sky. Personally I don't take that risk if I can avoid it by sending planes to a land airbase whenever possible. Only when I have no other choice do I split/merge carrier groups.
This is a known bug and while it is on the list of things to be fixed it actually is quite rare compared to many other bugs because once you have lost a couple planes once you will make sure not to make the same mistake again.

