[Southernhemispere]

As an example, travel north or south to the equator. At the equator make a 90 degree turn in any direction so you are heading east or west. Follow a straight line and you will hit the fabled Ice Wall. No such problem on a globe earth. Aeroplanes must be constantly banking to stay on path.

[nametaken]

A similar thing happens in regard to heading (navigation) on the globe. If you line up with a heading on a latitude line corresponding with your heading, you veer off course inevitably and constantly. Demonstrable on google Earth, as seen in this video. Latitude and heading are not the same thing.

Of course, there are no vast-cross-equatorial flights that I can find, so... that would be impossible to test anyway. Although many flights from Australia to Brazil work exactly like they would on the Globe, as can be seen with any booking agency.