NavList:

The Flightradar24 mobile apps and (desktop) web apps appear to be built on top of tools available on the Apple and Google platforms. FR24 has been around for a long time. I remember showing it to someone who was thrilled to have it as a "toy" back around 2012. By that time I had been using it for several years. The implication of this "great age" :) is that the developers were bound by the limitations of tools available in that era (think back to the dark ages of 2009... iPhones were first-generation back then...). Although Apple has since moved on to a standard global view in their mapping tools, the iOS app version of Flightradar24 still uses standard Mercator, as almost all tools did in the early internet period when Google Maps made that "terrible choice". 

What happens during polar flights? They fly off the map. The lat, lon data is updated for high latitudes, and you can track a flight by latitude and longitude, but when they meet the +85.0° limit, the aircraft icon just disappears off the Mercator map. There is no alternative display in that case. It would not be difficult today to create a rotatable globe display, but this project seems to have been a labor of love, and there may not be enough affection remaining for a major upgrade like that. The system is up, and it's running nicely. So airplanes fly off the map. This is life on a Mercator world! :)

It's worth mentioning that considerable portions of high latitude flights and certain other flights have large holes in their observed data feeds. These appear to be filled in with great circle segments.

Frank Reed