In Southwest (the airline), you connect to the wifi for watching the movie and where you are in air. But if you want internet, you pay.
I have some of my applications always Torified on my phone. I opened my 3d printer app to view its status, expecting a hard fail. And... it loaded!
But when you start using pluggable transports, like Obfs4, you can defeat pretty much every captive portal or traffic analyzer. I'm sure there might be a way to detect even these. But remember that the real test of detection is the GFoC.
Some piddly airline's offering of pay internet is not going to use nation-state level detection schemes.