The algorithm for determining the coordinates for switching the mode is simple and clear:
1. The copter catches GPS and determines in which country (gives data by phone)
2. If 1 is not satisfied, the GPS will determine on the phone.
3. If 2 is not met, the MCC number of the SIM card determines which country the SIM card belongs to.
4. If 3 does not work, the presence of a mobile internet and localized to IP will prove.
The copter store this value and change it only if he got new informations from GoApp.
For Apple iOS victims, there is also an easier way to get into FCC mode, if they use Litchi and do without the Go app.
Litchi can't Switch CE ↔ FCC !
Since the system has no GPS reception when neither the smartphone nor the copter has GPS reception, the MCC number of the SIM card is used to determine the location, a US Simcard suffices.
A US Simcard get collectors for example on ebay.com, the shipping costs are limited, as a simple letter is sufficient.
a.) Make your copter ready and register with the original GoApp at DJI.
b.) Go somewhere with the copter where neither the copter nor the Smartphone GPS or W-Lan receives (basement).
c.) Insert the previously supplied US SIM card into the smartphone (enter pin).
d.) Start up the system copter, remote and Smartphone with the original GoApp. Since the system has neither GPS nor W-LAN for location determination, the MCC number of the US SIM card is used. The copter will now switch to FCC and this will be saved.
e.) Well, as long as the GoApp is not used again, you can fly with Litchi in FCC mode.
Note: It's possible, do it with a borrowed Android device and modded GoApp. Then use Litchi only at iOS