I had some problems with the country not being set and the pi3 refusing to connect.
It’s some new feature specific to the pi3 and stretch i believe. You might have to remove the piaware wireless options and use the guide here: Raspbian Stretch Headless Setup Procedure - Raspberry Pi Forums
Be sure to set the correct code for your country. If the country is not set the pi3 will not work.
Probably flightaware people need to introduce a country setting that sets the country.
Regarding the other answer: gateway and nameservers should be configured by DNS, not sure why that would help without a static ip.