I have been traveling a lot recently between Baltimore Washington (BWI) and various south-western destinations - LAX mostly. I’m a bit nerdy so I tend to track the flight path using Flightradar24 etc.
I’ve noticed that never is the great circle route followed. For the initial 2 hours of outbound flight, the plane follows a path which ends up about 200 miles north of the great circle route. Rather than flying over the southern tips of Ohio and Indiana, the flight skirts the southern part of Chicago air space. Only once past Chicago and well into Illinois and sometimes even Iowa, the plane changes course and turns south-west for the final destination. The return flight is similar - up to the Chicago area and then a course change to BWI.
Southwest (in this case) flies hundreds of these flights a month (LAX, Vegas, Phoenix) so it must have an effect on overall fuel usage? Are there no well-established waypoints that would take the aircraft on a shorter great circle route?
You also have the jet stream which travels about 200 mph IIRC that does influence flight path (and prevailing winds dictated sailing path for ships for centuries even though the route is much longer in distance)
Additionally there was a flight in the southern hemisphere that the great circle would take it deep into Antartica, They chose to fly one direction around the Antartica ion one side and the other side of Antartica way going back to take advantage of the winds, and also avoid flying too far away from rescue if needed.
The Great Circle route is the shortest by distance.
All other things being equal, that should mean it’s also the best by travel time, fuel efficency, and cost. But everything isn’t equal. The jet stream will matter, as will major weather systems, normal wind, congestion in routes, controlled or restricted air space, etc. Also, there are rules about staying in range of suitable air fields in case an emergency forces a landing.
They will also stay in range of ground beacons, and their routes will be constrained that way. They don’t exactly have Waze or a Satnav to rely on. We would eventually things to go to GPS based navigation, which would save time, fuel, and money by improving routing, but the technology needs to be thoroughly tested and vetted first.
Scheduled commercial flights fly under instrument flight rules (IFR), even when the weather is good. That means they have to take orders from air-traffic control for the whole flight, except over the open ocean. ATC will require them to follow a sequence of high-altitude IFR airways (jet routes) over 18,000 feet. There are hundreds of jet routes crisscrossing the continent, but typically they don’t directly connect major cities along great-circle routes. The benefit of airways is that navigational aids can be laid out along the routes. I don’t know how they decide exactly which sequence of airways to guide a flight along. I imagine they take into account traffic and weather.
Private pilots (general aviation) flying under visual flight rules when the weather is good can typically pick their own route, as long as they avoid restricted airspace. However, they will often find it convenient to follow a separate system of low-altitude airways under 10,000 feet, also laid out with navigational aids.
Did you look at flights over a wide range of dates? This planned flight appears to approximate a great circle reasonably well and other flight plans and actual flights follow a similar route. I wonder if there was weather / wind on the flights you’ve flown that made you head further north?
All valid points except that I don’t think staying close to suitable airports is a problem in the continental US.
That article is a bit muddled. GPS has been used by airliners for a long time. The NextGen system seems to be more about optimising the route structures and other aviation systems to make better use of existing technology such as GPS and also some near future tech.
It’s true that the airways have historically been constrained by ground navigation aids but that hasn’t really been necessary for some time. I suspect that the traffic density in the US makes it difficult to have optimum great circle routes everywhere.
I flew from Boston to Tokyo and back, and was interested to see that the trip west was approximately the great circle route (trimmed in a little to avoid Russian airspace but the return trip pretty much followed a latitude line. I assume we picked up the jet stream on the return trip, and that made up for slightly more miles.
The route you describe isn’t really that much longer. Going over Chicago and Des Moines only adds 34 miles, or 1.5% of the distance. It wouldn’t take much wind on the more direct route to make that diversion worthwhile.