Max Planes decodes the data from ADS-B transponders and plots the data on a map. You need to connect a USB device and run a BEAST server (such as Dump1090 Mac Server) in order to view this data. Then, you connect to another computer running Dump1090 over a local area network to watch the planes it sees. There is no need for the Internet to view live data from planes.
You can see the altitude (not position) of planes in the spotting list. You can watch multiple data sources at once, save recordings as a file and re-watch them later.
v2.1 [Jul 23, 2021]
Fixed an issue with In-App Payment validation that was causing the app to exit unexpectedly.
