Question about alternate flight paths on long haul routes
Posted by Kwinten@reddit | aviation | View on Reddit | 8 comments
Hi /r/aviation community!
I was checking out the recent flights of flight route NH205, which is a direct flight from Tokyo to Vienna.
I noticed that recent flights same to take completely opposite paths: one day, they fly West, mostly across land, and other days, they fly East over North America. Both paths appear to take approximately the same amount of time.
I found it quite a curious phenomenon, as I am a complete layperson when it comes to aviation. Is this common for flights of this kind? For what reasons may airlines choose to take one path vs another? Would it be purely based on something like predicted head or tailwind or other factors? I couldn’t really find any other answers to this question online which piqued my curiosity even more.
mckenzie_keith@reddit
I think they also avoid conflict zones.
Typical-Zebra8920@reddit
Most airlines avoid Russia, there are quite a few other areas one can not fly including the obvious ones like Ukraine.
Typical-Zebra8920@reddit
I fly between London and Tokyo and the shortest route used to be back and forth through northern Russia, obviously not available to most airlines at the moment.
Eastbound you have the jetstream giving you a good tailwind, in the way back it’s a choice, the return route westbound is against the wind and can increase the flight time considerably.
The other option is to fly eastbound over Alaska and northern Canada , unfortunately there are not many alternates available for ETOPS operations ( you have to stay within a certain time away from a suitable available alternate usually 180 minutes ) if any of these alternates are unavailable you may have to fly further south which can make flying back west the quicker flight time.
From London it’s usually east bound on the way home but with Austria being further east I imagine it’s more likely that it could vary more depending on wind and alternate availability
praetor450@reddit
There are various factors that go into what route a flight will take.
Shorter flights will generally have very similar routings for each flight given the short distance and sometimes if the airports are close enough the departure routing for one airport is very close to the arrival of the other. There way more factors that can dictate the specific routing such as air traffic control preferences and standard routing between certain airports.
For long haul flights when a flight plan is going to be generated (focusing only on the routing for this example), the dispatcher might select a certain criteria the want to prioritize, generally it comes down to lower overall costs or time on enroute.
The system then looks at all the factors and tries to optimize for that. Let’s say they selected reduced time because the airplane is running late from a previous flight. The system will then will try to find every place that the winds are favourable (tail wind) to save time, which won’t always be a direct routing based on winds. Then other things such as airspace closures could affect if they have to go around certain airspace.
From what the system outputs then the dispatcher might make adjustments if there is weather enroute or reported turbulence to make the flight more comfortable sometimes at a cost to what they were trying to optimize. It’s a compromise, but there is a lot of that in aviation.
Then they keep making adjustment until the flight plan is satisfactory to what ever metric they were instructed to use.
The process can be more involved than my very basic and simple explanation. However, that’s how you can sometimes see flights one day have a certain routing and the next flight have one that is very different.
mduell@reddit
Primarily winds, also other factors like overflight fees.
aucnderutresjp_1@reddit
Weather can change from day to day, just depends what the flight planning teams decides makes the most operational sense.
Kwinten@reddit (OP)
I figured it is most likely completely related to weather.
I just thought it’s interesting that it’s such a dramatically different path. I guess the route is just in that sweet spot where you can cross half the globe going either way and do it in approximately the same time.
aucnderutresjp_1@reddit
A few months back, JAL and Finnair raced to Tokyo. Departed around the same time, went totally different ways. Probably have days where the same happens too.