Comment by treahauet

This article suggests that positions are estimated when the aircraft isn’t in a coverage area. https://thepointsguy.com/2017/09/how-flight-tracking-sites-w...

It’s also worth noting that FlightAware has partnered with Aireon (owned by Iridium according to Wikipedia) to put ADSB receivers on satelites that were launched with Iridum’s NEXT satelite constellation in low-earth orbit. Sounds like that data is not yet included in the free data FlightAware provides on its website, but is available commercially. https://flightaware.com/commercial/aireon