[snip]... Why is there no tracking data for ocean crossing flights in the southern hemisphere?
If the Earth were flat, shore based tracking systems would be able to track these flights using line of sight technologies. Given that they can't, due to the curvature of the Earth, you've basically just proven that the Earth is not flat.
Welcome back to reality.
That was a stone cold explanation...or should I say (because of this topic) a stone age cold explanation!