For Southern hemisphere flights thats probably in the right ball park, although obviously there has to be some account for the fact that we not know exactly where everything is. The best way to some constraints on this is to see if you can close the triangle. Take three popular air routes that form a large triangle. The large is important because it will tend to convolve out any uncertainties in flight speed, effects of acceleration/climbing to cruse altitude. I'd suggest something like New York - Buenos Aries - Sydney, something like that. If you assume that aircraft travel at about 500 mph, look at the flight times and see how far apart they are. If the resulting triangle doesn't close then the Earth isn't flat. Though its possible the errors would be to big even with those differences, particularly as I don'y know how close to the shortest route planes fly in practise, certainly jetstream cause them to adjust.
We can say something about where things are using natural phenomena, for example tracking migratory animals around the oceans. I guess marine biologists might be in on it. I think the tsunamis of recent years also provide some nice evidence. The last one in Chilli caused small tsunamis/anomalously high tides around the Pacific rim, the times of these can be quite accurately tracked by their trail of destruction/media coverage/surf report. Again I would argue that the times were indicative of a round Earth. Or at least a Pacific ocean where NewZealand was much closer to South America than Japan.