[UniversalTruth]

Why Do Aircraft Pilots Do THIS?!? From New York, USA to Cairo, Egypt.



Guys, do you have a reasonable explanation why they do such long routes?

I have noticed this article but it doesn't explain a lot.

http://en.wikipedia.org/wiki/Flight_planning

http://en.wikipedia.org/wiki/Jet_stream

Even after taking into account a consideration about following the jet streams.

They say:

Airline routes between Los Angeles and Tokyo approximately follow a direct great circle route (top), but use the jet stream (bottom) when heading eastwards.



Approximately?!?

[AlphaWolf]

because the earth isn't flat

[UniversalTruth]

Originally Posted by AlphaWolf

because the earth isn't flat

This.... is not a reasonable explanation as of why they do follow SO MUCH longer routes.

It is obvious that they don't take a direct course in which they will only have to correct it by lowering the altitude since because Earth is not flat and if you take a direct course straightwards you will fly out of the atmosphere.

[Florin]

Those elliptical lines are not an actual detour but an effect of mapping our globe onto a 2D map. The airplanes do very much take the path involving the shortest possible amount of distance covered.

[UniversalTruth]

Originally Posted by Florin

Those elliptical lines are not an actual detour but an effect of mapping our globe onto a 2D map. The airplanes do very much take the path involving the shortest possible amount of distance covered.

That's exactly what I'm trying to explain. These elliptical trajectories are so elongated that you can't explain them with Earth's shape.

ETOPS is part of the explanation but it doesn't explain everything.

http://en.wikipedia.org/wiki/ETOPS

[pcchen]

Originally Posted by UniversalTruth

That's exactly what I'm trying to explain. These elliptical trajectories are so elongated that you can't explain them with Earth's shape.

That's because if you view it with Google map, which uses a Mercator projection, has a very high distortion at higher latitudes.

For example, you can view the track of a satellite running a sun-synchronous orbit here:

http://www.n2yo.com/?s=28254

(zoom out to see the whole earth)

You can see that it's "highly elongated" but the satellite is basically running a roughly round orbit (i.e. similar to a great circle) around the earth.

[Simon F]

To UT.
Go by a globe and a piece of string. Pin one end on the destination, and pull the string so it's aligned over the depature point.

[Chalnoth]

Originally Posted by UniversalTruth

That's exactly what I'm trying to explain. These elliptical trajectories are so elongated that you can't explain them with Earth's shape.

ETOPS is part of the explanation but it doesn't explain everything.

http://en.wikipedia.org/wiki/ETOPS

A great circle is the shortest distance between two points on a sphere. Yes, great circles look highly distorted on many map projections. But they really are the shortest path.

[UniversalTruth]

Originally Posted by Chalnoth

A great circle is the shortest distance between two points on a sphere. Yes, great circles look highly distorted on many map projections. But they really are the shortest path.

It would be nice if you prove it.

The airplanes don't simply follow "great circles" as shown on the second image here, but insted they follow not so logical much elongated routes which have nothing in common with simple "great circle".

Go to the site and see it yourself.

[Simon F]

Originally Posted by UniversalTruth

It would be nice if you prove it.

The airplanes don't simply follow "great circles" as shown on the second image here, but insted they follow not so logical much elongated routes which have nothing in common with simple "great circle".

Go to the site and see it yourself.

Well, they do have to avoid certain airspaces and there was (might be lifted now) a safety (?) ban over flying directly the arctic etc. Further, if there are local weather conditions, e.g. a suitable tail wind they want to use, or head wind, bad turbulence or storms they wish to avoid, then I believe they do change the route.

[Zaphod]

Two engine aircraft also fly different paths than four engine ones, due to requirements about how far you can be from an alternate airport at any given time. I assume this implies a more northerly route.

[Chalnoth]

Originally Posted by UniversalTruth

It would be nice if you prove it.

The airplanes don't simply follow "great circles" as shown on the second image here, but insted they follow not so logical much elongated routes which have nothing in common with simple "great circle".

Go to the site and see it yourself.

Barring the situations that Simon presented, yes, airlines tend to follow great circles. But what, specifically, do you want me to prove?

[Grall]

Originally Posted by UniversalTruth

The airplanes don't simply follow "great circles" as shown on the second image here, but insted they follow not so logical much elongated routes which have nothing in common with simple "great circle".

Considering the price of jet fuel and the recession of the economy, poor margins and profits in the aircraft industry and similarly related factors, you can be sure that airlines plot the absolutely shortest routes they are allowed to, legal/safety and weather factors considered of course...

[PixResearch]

Isn't the reason for the two paths just simply the direction you're travelling in?

If you're heading west you follow the great circle route because it's the shortest distance between two points. If you're heading east then you might be better off taking advantage of the very high speed tail wind of the jet stream to save some fuel. It likely depends on where exactly the jet stream is pointed that day and how fast it's moving on any given day.

The paths are likely approximate to avoid other planes, turbulence, etc but I think they pretty much do their best to stick to one of those paths.

[Mize]

This is a comical thread!
Airlines can tell you the cost of fuel in $ per gram of payload and people think they take longer routes?
Sure there are airspace restrictions (for instance sometime my flight to Beijing takes longer if Russia closes their airspace) but, aside from that and natural disasters (volcanos), airlines are very good at plotting the most fuel-efficient flight plans possible based on wind speed, wind trajectory and distance.

If you fly from Beijing to Seattle, for example, sometimes you'll flight with more arc (slower jet stream) and sometimes you'll fly more along a latitude (faster jet stream). Rest assured, however, that whatever the path, it's the one that the best forecasts and models predict will use the least fuel.

[UniversalTruth]

Originally Posted by Mize

This is a comical thread!

Thanks for the nice opinion.

Originally Posted by Mize

Airlines can tell you the cost of fuel in $ per gram of payload and people think they take longer routes?

Yes, but it's you who pays the bill in the end, not the airlines.



Please, for God's sake, don't tell me that Minneapolis, Saint Paul (MSP) is in that direction.

[PixResearch]

Looks about right...

The great circle for that flight is here:
http://www.gcmap.com/mapui?P=AMS-MSP

There's curently a 140mph jetstream blowing north where the plane is shown. There's not much point in fighting the jetstream so they're probably being blown further north and more fuel efficient to go with it a bit:
http://www.netweather.tv/index.cgi?a...etstream;sess=

[Grall]

I think Mize considers your thread comical because it wouldn't make any sense to plot longer routes for no logically discernible reason. It doesn't cost more just in jet fuel, but also in wear on the airframe, engines and so on, personnel cost for the crew, increased inconvenience for the travellers - tons of factors that start piling up.

What reason do you think airlines have for flying longer routes than neccessary?

Please, for God's sake, don't tell me that Minneapolis, Saint Paul (MSP) is in that direction.

Haven't we been over this already? Curvature of the earth an shiet, ring any bells? Look at how a non-equatorial satellite orbit looks when plotted on a map - often a sinus-like curve. Why would a satellite fly in a curve over the earth? Answer, it doesn't - of course. Oh, and 3x



PS: yes, airlines don't pay higher costs - travellers do. But higher costs = fewer travellers = lower profit, so it does cost airlines too. Elementary stuffs!

[Mize]

Originally Posted by UniversalTruth

Thanks for the nice opinion.

Well, come on, you seriously think you're onto something?

Yes, but it's you who pays the bill in the end, not the airlines.

Are you serious? Go track airline profit as a function of oil prices. They all lose big money when fuel prices go up as they aren't a collusion monopoly like the oil companies.

Please, for God's sake, don't tell me that Minneapolis, Saint Paul (MSP) is in that direction.

Of course it is. Go get a globe and a piece of string. Now put one end on the start and another on the destination - that's the "great arc" and the shortest distance.

Of course that shortest distance makes no consideration for the jet stream or weather which the airlines take into consideration.

[zed]

there was a experiment done ~4 years ago (when gas prices were very high) with a big commercial jet.
IIRC flying from europe to sydney (hmm stopover) anyways they flew about 20% further than normal, extra 2 hours or so but used about 20% less gas, they done it by using wind patterns.
i.e. the savings were quite big

[tongue_of_colicab]

Would be interresting to see how that turns out if you take in to consideration the extra stress on the airplane and aircrew along with the fact that flying for 2 hours longer means you lose 2 hours in which you could have an additional 300+ paying passengers going someplace else with your aircraft.

[Mize]

fyi, the airframe stress at cruising is negligible. >>90% is takeoff and landing.
Crews are relatively cheap and, on long flights, a couple hours won't shift capacity. On shorter flights crew and time are more interesting, but fuel is the #1 cost.

zed, 20% = 2 hours means a flight of 10 hrs - it wasn't Sydney mate. Hell Los Angeles to Sydney is like 18 hrs, right?

Anyway, as I said, the airlines aim for the most fuel efficient route. Always.

[RudeCurve]

Originally Posted by Mize

fyi, the airframe stress at cruising is negligible. >>90% is takeoff and landing.

Are you sure about that? About 2/3 of every flight that I've taken there was at some point during the flight some scary turbulence that shakes the whole plane as if you were experiencing an earthquake.

[aaronspink]

Originally Posted by Zaphod

Two engine aircraft also fly different paths than four engine ones, due to requirements about how far you can be from an alternate airport at any given time. I assume this implies a more northerly route.

With the current twins doing transpacific and transatlantic flights, this really isn't true anymore. Almost all the large twins are using with ETOPS-180/207 or ETOPS-240+. The GE equipped 777s are approved for ETOPS-330, and the 787/350 are planning for ETOPS-330/350 as well.

ETOPS-180 is enough to make the flight paths the same for all aircraft on all routes except for deep southern ocean routes (South Africa<>South America, Australia<>South Africa/America).

So anything crossing the northern oceans regardless of 2 or 4 engines are flying the same paths.

[aaronspink]

Originally Posted by UniversalTruth

Yes, but it's you who pays the bill in the end, not the airlines.

not it is the airlines.

Please, for God's sake, don't tell me that Minneapolis, Saint Paul (MSP) is in that direction.

Only 2 factors generally play into the routes airlines take: Great Circle and Jet stream. In this case the optimal route for GC cuts across the UK, but there is a high speed jetstream in the way that they would have to run against which makes no sense to do, to they are going further north in order to bypass it. You can be sure that airlines take the most optimal route possible. They have entire teams plotting courses for flights along with a significant amount of computing power to plot optimal courses.