I think we’ve established that jet streams have nothing to do with it (for one thing, 19,000 feet is too low for jet streams).
But could aviation dopers clear something up? The Wikipedia article talks about jet streams as narrow, transient things that are not continuous and come and go of their own accord. But the same article asserts that commercial aviation exploits jet streams to cut west-to-east travel time, and conversely makes out that east-to-west flights must carefully avoid them.
This seems like a contradiction. It seems that if you randomly fly around in a jet at typical cruising altitudes, you are very unlikely to encounter a jet stream. Is the Wikipedia article mixing up jet streams with mere prevailing winds? Or are the effects of a jet stream felt over a wider area than the “1 to 3 miles” of the Wikipedia article? That is, it is not so much an isolated tunnel of fast-moving air, but more a wider region in which air tends to move faster?
I’m not an aviator, but it seems clear enough to me. If the cost of altering course to exploit (or avoid) the jet stream is offset by the benefit of doing the same, then that’s what they’ll do. For short hops that aren’t anywhere near a jet stream, it doesn’t enter the equation. On a long eastbound haul, even if you’re not close to a jet stream, it may make sense to go out of your way to catch it. If you’re close to the jet stream on a westbound haul, it makes sense to get out of it as soon as you can.
I’m sure they also take lesser prevailing air currents into consideration wherever it makes sense. Depending on the route, the regional weather patterns might be more a more important consideration than the jet stream. It all depends on where you are and where you’re going.
Yeah, but it’s not like there’s just one jet stream running like a convenient conveyor belt from west to east. It meanders and breaks down, or just doesn’t exist, for long stretches. Seems like following a jet stream would most often involve major diversions, which would probably defeat the object of following it in the first place. Maybe they only exploit jet streams when the conditions are just right, but that would mean airlines employing a radically different routing strategy on a few random occasions. With the strong emphasis on safety and routine in the aviation industry, this seems unlikely.
The jet stream is random, but within a fairly well-known degree of variance. For certain east-west routes, I imagine they have some pre-existing alternate flight plans that can exploit the jet stream if it’s not too radical a diversion. I know the Tokyo-Atlanta haul is always 3 hours shorter on the eastbound leg due to heavy overlap with the jet stream. For New York to LA I doubt the jet stream even figures into the flight plan except for minor correction to avoid it at certain times of the year.
If you’re getting a satellite feed off of an internet site then you aren’t getting accurate information. There is no radar service over the ocean to feed the system. If this is the case you were seeing the last reported altitude due to a glitch in the system (radar would normally cover the rise to 38,000 feet).
Planes will fly at lower altitudes due to mechanical problems such as a pressurization leak or a rudder bleed system. However, they would not make an ocean crossing under such conditions. I’ve seen it done in legs less than 2 hrs long and then only under ideal conditions.
Really? It doesn’t look to me like there should be much overlap at all on that route. The geodesic from Tokyo to Atlanta would take you mostly over Alaska and Canada, while the jet stream is mostly in the vicinity of 45 degrees latitude. It seems like staying that far south ought to add more distance than it’s worth.
Post number 6 in this link (messageboard for flyerlink.com) shows Nov 16 2008 flight paths from Narita (NRT)-Atlanta (ATL) and vice-versa.
Summary for those who don’t want to click through:
It appears that going over Canada/Alaska is the shortest path, and it is used when going from ATL to NRT, but the path is significantly further south on the return trip to take advantage of the jet stream.
Actually, the Jetstream wiki shows a similar path from Tokyo to Los Angeles.
