Another idea (if it can be done): Keep the initial number of days until 'autoplay' starts, 3,5,14, etc. remain the same. BUT after one or more planes are in autoplay, have the autoplay feature take effect as soon as the last plane, not in autoplay, has moved.
This might encourage some players to play in the larger games without fear that one player will make the game last for months.
Another irksom situation in when a plane on autoplay actually wins the game. I had one recently (a four player game) where two planes were down and the other two wher moving slowley in autoplay. Eventually one of these dorks wandered off the boark and won. I think a "pilotless" plane should not be able to win a game.

THX
Bombadil