For Education: Actual Route vs Great Circle

I’m a tutor on math and physics. Expanding upon planar trigonometry, I also teach spherical trigonometry. The demonstration of its properties is quite easy when I use the case of qibla bearing since only direction is required between two places.

I went further by plotting flight routes. Some manual calcs with spreadsheet will produce points for great circle path, to be compared with actual routes from FlighAware. All was good, but some cases really piqued my interest.

DAL83, DAL296, and, especially, SIA24 deviates quite much from great circle path. So, I have three questions about the cases.

1. Is it common for flights to not follow great circle path?
2. Do those away-from-great-circle flights have enough fuel, like, already within planning consideration?
3. About SIA24, do you know why it flew path significantly different from great circle one, adding about 1000 km to the distance?

Here are the plot and the link to the data. I use GPS Visualizer to plot the path. Orange indicates great circle path, blue the ADS-B tracklog.

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Not a pilot, but there will be other factors at play rather than just the straight line/shortest distance. For CDG-ATL the most likely answer is the North Atlantic Tracks. So you can’t just fly wherever you want to. I believe there are many tracks, each day they will use different ones depending on the weather and winds.

For the other two, again my guess would be that the prevailing winds on their planned flight route were more favourable than going in a straight line. Winds can easily be 100mph+ so on a 18hr flight you make up that extra 1000km pretty easily.

Noice, thanks. So it’s not just just about geometrical considerations, but also meteorological and safety ones. Nearest isn’t always the fastest nor safest.

That adds a great bunch to my course’s narration. Much appreciated.

That info about wind leads me to this article.

Winter Winds: How Singapore Airlines’ New World’s Longest Flight is Saving Time (and Fuel) by Flying Farther

Thanks for the pointers.

Another reason for non-GC routing is that the direct GC route may take you too far from a suitable diversion airport. See ETOPS - Wikipedia

Also, geopolitics - some carriers are forbidden from using certain airspace, and airlines are also understandably uncomfortable about flying over conflict zones. That can lead to some weird routes.