I want to buy a used iPad Air 2 +4g from the internet.
Most of them say that"will work with Verizon AT&T T-Mobile network".
Will their gps work with my P3A or i need an unlocked one?
GPS will work regardless since there is no need for a data plan for the GPS to work. If you want to access the internet while in the field without tethering, you will of course then need a data plan.
I use an Air 2 Celluar without any network account. It works great.
You can cache your Flight Map from home or from any wifi network.
A SIM card will only be needed if you want to stream live video to your own YouTube channel, or if you want to connect wirelessly to the Internet.
Yeah, iPads are not "locked" like iPhones can be. Any SIM card will work if you wanted cellular. I buy cellular models because I want GPS, non-cellular models don't have that, and anytime you want (on a trip, etc.) you can buy a month of data with no contract.
I am using mine like that right now as I am sitting at the pool while I am on holiday visiting my parents.