I dont have iPad or iPhone, but fo have an old phone Samsung Galaxy S4 which I no more use as phone, but as mini tablet, because it became defective, and will not pick the SIM card.
I searched Google Play for “adsb” and found many Apps., as shown in screenshot below. I already had Flightaware’s Flightfeeder which does not display map when internet connection is dropped. Just to try, I installed “Adsb Receiver” and “Ads-b on Android” (the top two on the screenshot). Both display map and data without internet connection, but I did not find any method to use these as server to feed data to tracking sites like Flightaware, or to feed data to dump1090 of my RPi, when the phone is on the same LAN as the RPi.
Has anyone tried these?