Like with areas with strong tailwinds, do airlines ever route trips over areas of uniform, mildly ascending airmasses, such as benefit sailplane activties? Theoretically, this could reduce fuel burn on overland legs (to the extent that undue turbulence is avoided).

Faro

[Edited 2009-05-13 03:22:41]

I'd expect that the scale of such atmospheric effects would be too small to warrant the change in routing to use them. And most planes cruise above the weather.

When I lay out flight plans for the widebodies we schedule in the office I work in, we use different settings of seasonal winds - i.e. 85%, or 75%, depending on the mission. This is mostly just to get a ballpark figure on fuel burn and operating costs. I assume just like intra-US IFR routing, trans-atlantic and trans-pacific routing has preferred routing and travel lanes for crossing the oceans and polar routes that actually must be filed for on the flight plan.

But once you are in the air the game changes significantly. A lot of times pilots' can request deviations or new flight routing in order to hop in the jetstream or ask for different altitudes to avoid turbulence or lessen a headwind. This is especially true for east-bound trans-continental flights in the US. I've read and heard plenty of stories of planes getting in the 700MPH ground speed realm because of a serious tailwind.

Its like the flat escalators underground at ATL - you may have to walk in the wide lanes between the escalators if the faster escalator lanes are too crowded, but if there is room and clearance, you can hop on, exert the same amount of work, but reduce travel time and overall energy used.  

Unless you are about to sit on the ATL-NRT flight for an endless amount of time, in which case I walk the mile

Well, thermals are only one of the types of rising air mass that are out there. It might be feasible to cruise in portions of 'mountain wave' in the lee of a large, relatively straight mountain range. Examples could be the Andes and Rockies, though I don't believe this is done in practice.

This mountain wave lift is associated also with strong turbulence and was responsible for breaking up a BOAC 707 over Mount Fuji back in the day. It shows as lenticular clouds running parallel to the mountains. Whereas I wouldn't wedge a large jet in it, something like a small business aircraft might get some benefits from it - if they didn't mind bouncing around a bit, of course  

Most smaller lift source, like thermals and ridge lift, are too small, or meaningful only too near the ground, to be of much use to an airliner. Mountain waves might be big enough, but are often very, very rough (actually pretty much any of the sources of lift can, and often are, pretty turbulent) - not something you really want to subject passengers to.

I can personally vouch for the (potential) roughness of mountain waves - having had one crack my skull against the canopy hard enough to make me see stars - and leave a very nice lump. But other than the lump, that was one *heck* of a soaring day! I topped out at over 22,000ft.  

Quoting Rwessel (Reply 4): Most smaller lift source, like thermals and ridge lift, are too small, or meaningful only too near the ground, to be of much use to an airliner.

What about depressions? From my climatology primer, they are areas of gently rising air with regional extent.

Faro

Quoting Faro (Reply 5): What about depressions? From my climatology primer, they are areas of gently rising air with regional extent.

The key is that the air needs to be rising fast enough to be useful, AFAIK, the lifting of the low pressure air mass is pretty slow overall (although it can be locally more intense), although I can't seem to find any typical numbers on that at the moment.

But aren't all those mentioned effects large contributing factors in the formation and location of the jet streams, so airlines are using them indirectly anyway?

jet streams are the result of continental air masses.