22

I fly often between London and east coast USA (usually New York or Boston) - and every single time up until now the flight would go along the great circle route.

I flew yesterday from Boston to London - and to my mild surprise the flight path went a lot further south - almost along the parallel. I can't get the full flight radar replay (I guess you need a paid membership for that), but here is a picture I took of the inflight progress display a couple of hours into the flight.

enter image description here

This was flight VS158 (actually renamed to VS1158 due to change of destination airport).

Why would such an unusual path be chosen? I understand that it's unlikely we'd know the exact reasoning for this particular flight, so I'm wondering how and why decisions to route this way are made.

Edited to add: the flight was on 6 August 2019.

  • 1
    Why unexpected? On my East-bound flights, this is the most normal track. Just on west-bound flight one usually flight much more on North. – Giacomo Catenazzi Aug 7 '19 at 14:15
  • 11
    This might be a better fit for Aviation; most passengers don't notice such things, so long as they arrive on time. – choster Aug 7 '19 at 15:36
  • 1
    @GiacomoCatenazzi "unexpected" to me, because this is the first time I saw this in my 50+ flights from BOS to LON. – Aleks G Aug 7 '19 at 15:40
  • 4
    Flightradar24 will give you full replays of everything in the last week, for free. Your flight is here. – David Richerby Aug 8 '19 at 0:31
  • You might want to save the images of recent flight paths for future reference here. – smci Aug 8 '19 at 10:56
48

The specific answer concerning your flight is that yesterday there were abnormally fast westerly winds over the mid-north-Atlantic, which many eastbound flights took advantage of.

You can still see them, as of the time of this edit, here:

https://www.ventusky.com/?p=43.5;-32.4;3&l=temperature-200hpa

(shown are winds at a pressure altitude of 12000m, approximately the cruising altitude of a plane)

10

In short, your flight followed what is known as a "North Atlantic Track".

These are paths in the air above the North Atlantic which are used by air traffic control to effectively manage aircraft separation in the North Atlantic (where there are lots of planes and little radar coverage). Planes' entry into these tracks is managed for safety reasons and individualised flight plans are avoided.

The specifics of where these tracks are is determined by factors such as winds/jet-stream among many other considerations. There are also multiple tracks in operation at a time, meaning that a BOS-LHR flight will likely be on a different one than ATL-MAD (for example).

The Wikipedia article on this is pretty good!

  • Ah! Very interesting. I've travelled london to/from boston over a hundred times of the last 10 years - and this was the first time we didn't go great circle route. – Aleks G Aug 7 '19 at 10:55
  • @AleksG if you look at it in detail you'll find that the tracks approximate a great circle route but do not follow it exactly. When the winds are strong, the benefit of diverging from the great circle is relatively more pronounced. – phoog Aug 7 '19 at 11:01
  • 1
    @AleksG air speed or ground speed? The air speed will almost always be about the same, which is why airlines will seek to avoid headwinds when flying west and to catch tailwinds when flying east. – phoog Aug 7 '19 at 11:08
  • 1
    @phoog Both actually. The flight completed very fast. It left on schedule and arrived about 40 minutes ahead of schedule. – Aleks G Aug 7 '19 at 11:09
  • 3
    @phoog It would definitely be groundspeed, not airspeed. No airliners fly at 600 KIAS. That would be supersonic at that altitude. Even 600 knots true airspeed would be supersonic above around FL250. From FL350 up through the Tropopause, Mach 1 is around 573 knots true airspeed. – reirab Aug 7 '19 at 22:32
2

I've seen this happen many times when flying from China to America. The thing is, airplanes don't actually care how far away the destination is, but rather they care about the flying time. When you are flying against the wind (as you generally are when heading west in the northern hemisphere) your best bet is the shortest route, hence flights heading west take the great circle route unless there is a political reason to do otherwise. (I've seen plenty of small zigs to avoid entering airspace and I've once seen a zig of hundreds of miles when they didn't want to fly anywhere near North Korea.)

However, when heading with the wind you can often find it is more advantageous to take the path with the most wind than to take the shortest path. I've seen a 200 mph tailwind.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.