The game really got me into keeping my airline grow and so far it's been very much fun, but my airline got so big now that certain tasks become a bit tedious and uncomfortable and in some moments I wished there were some features making life a bit easier, so here's my few suggestions:
Checkboxes for lists like leased gates to mass-return them and replace them by a terminal or for cancelling a lot of orders etc. if checkboxes are viable to implement. This would make things much faster, given that an accidental purchase of 30 planes need you to seek the plane type 30 times in the list, hit the cancel order button 30 times and wait for the page to reload 30 times.
Plane retiring and replacement is tedious right now, replacing a bunch of used up 707s needed me to have a few sheets of paper and take detailed notes on plane name and the routes the planes served. Maybe following ideas make it a bit easier:
* Sorting planes by remaining cycles for finding used up planes easier
* I second Gary's suggestion with the ability to transfer flights from one plane to another
* Intoducing an indicator showing that a plane is out of order due to used up cycles, e. g. in the plane view or a list of planes that are out of order or the planes get their flights removed and there'll be a list of affected routes due to planes that used up all their cycles?
Add the option to revert a flight's direction in the plane schedule window alongside the time and day changing options - It'd be cool to be able to flip the flight direction when you messed up a thing in the plane schedule since that'd be at least a bit faster than removing all messed up flights and re-add them.