Windows selling helicopters?

Does anybody know how we can sell our helicopters? We can sell planes to replace them, and we used to be able to do the same with helicopters; now it seems helicopters are not able to be sold. Any suggestions?

Open your warehouse using the crate icon at the bottom of your screen. Click on the helicopter icon and it gives you the option to sell your helicopters. I am pretty certain that you can sell the pad after you have sold the helicopter but I don't remember how at the moment. Hope this helps.