The existence of the non-stop Sydney-Johannesburg flight route is only possible if Earth is a sphere. We can find that out by comparing its duration to the same route but with a stop.
There are other Sydney-Johannesburg flight routes, but with a stop, like in Dubai. Flat-Earthers use the existence of these routes to “prove” a flat Earth. In reality, it does not mean the non-stop route does not exist & it is not difficult to verify that the non-stop route exists.
On a flat -Earth map, Dubai lies almost in the path of the Sydney-Johannesburg flight route. And therefore, if Earth is flat, then the non-stop Sydney-Johannesburg duration and the duration of the Sydney-Dubai-Johannesburg route should be comparable.
However, the non-stop flight is around 12:35 hours long. And the flight with a stop in Dubai is around 13:40 hours and 07:55 hours long on the two legs, with a total of 21:35 hours long. The durations do not add up in the flat Earth model.
On the other hand, everything is consistent if Earth is a sphere. In reality, because Earth is a sphere, the non-stop Sydney-Johannesburg travels over the southern Indian Ocean; it does not go anywhere near Dubai.
- Sydney-Johannesburg: QFA63, QFA64
- Sydney-Dubai: EK412, EK413, EK414, EK415
- Dubai-Johannesburg: EK761, EK762, EK763, EK764