For now, I can spend golden planes on arrivals and the purchase is permanent. I don’t need to spend GP from time to time in order to keep the arrivals. It is very important for me as I would love to keep my airports with as many arrivals from various airlines as possible, but at the same time I don’t have the time needed to collect keys for unlocking arrivals due to work. I am a little bit worried if arrivals cannot be purchased anymore or if my purchased arrivals are no longer permanent ones.
The new system is complicated, but check out one of the previous dev blogs.
Currently, you can also buy destinations with Wollars
Sorry for my false memory. I actually converted GP to Wollars in order to purchase arrivals