Sadly there is no real GPS built into the fireOS/Kindle devices, so once you loose wi-fi you will no longer have a location.

It is however possible to add an external bluetooth device to make it work.

SkyCharts XC has been tested with the XGPS 150, if you know of others please let me know.

It only takes a couple of steps to hook it up. This is how:

• Become a developer on your device.
• Enable ADB to your device.
• Enable Mock locations on your device (right under ADB in link above).
• Download the latest version of Bluetooth GPS for Android,
  and install the APK on your device.
• Pair your XPGS device. Then run the BT GPS app, and select XGPS 150.

SkyCharts XC should now see your location even without wifi!

Also remember you can use X-Plane and Elite and have SkyCharts XC pick up the location! Please see here how to configure X-Plane.