Thanks for posting!
If this works as expected everywhere else, then the internet provider may be blocking outbound connections to port 5003 (the port FileMaker Go uses to communicate with the host). It's common for connections like the one you might find on a flight to have a wide range of outbound ports blocked as a way of limiting the types of services used. Unfortunately, if this is the case, you probably won't be able to get a request to allow outbound access through 5003 completed in time to actually use it on this flight.
I know it's too late, but next time try to setup a VPN thru the iPad. It might help. Best wishes.