On Wed, May 05, 2010 at 11:29:36AM -0400, P. J. Alling scripsit: > On 5/5/2010 10:17 AM, Graydon wrote: > >On Wed, May 05, 2010 at 09:58:58AM -0400, P. J. Alling scripsit: > >>I've do a little research, and it appears that no matter what the > >>"Mail's" agenda, there was little enough reason for a blankett ban > >>air travel. Plenty of blame to go around. > >Sure there is. > > > >The ash is not evenly distributed. The ash is not predictably > >distributed. There's, oh, one chance in a hundred thousand of an > >emergency and some lesser chance of a crash if an aircraft flies through > >the ash cloud, and because it's not a nice neat plume it's difficult to > >route around. (It could well be worse than that; there isn't a large > >body of statistical data on flying wide-body jet aircraft through ash > >plumes because on those few occasions when it has been done it has gone > >extremely wrong.) > > > >There's between 22 and 25 thousand air movements in the affected area > >of Western Europe every day. So one chance in 5 some flight has an > >emergency, every day. Four chances in five that you'll get one in a > >week. Do that for two weeks and the odds of a crash get peskily close > >to certain. > > > >Despite which, many of the flights wouldn't have been affected at all. > > > >It's just that the one that *did* get the total engine out and crash > >would have been correctly describable as completely predictable. > > WTF? The US didn't blanket ban air travel after Mount St Helens, > there was no continent wide ban and no air crashes. Yes, there were > several planes that made emergency landings from engine damage but > they were in the air in the area of the volcano when the eruption > occured. Most delays were caused by ripple effects from places > actually effected by the plume, and actual air sampling gave a very > good idea of where the problems areas lay.
St. Helens wasn't the same sort of eruption; St. Helens blew off the top third of the existing cinder cone and scattered that through the atmosphere, it wasn't producing large quantities of ash in the eruption, and the majority of the fine ejecta wound up very high due to the explosive nature of the eruption. (the less fine ejecta came back down.) This particular Icelandic volcano melted its way up through a glacier; volcanic ash is just lava that has cooled into fine sizes -- think powdered glass -- and going up through cold water produces a lot of ash that doesn't go extremely high. So there's lots of ash and it gets up to levels where the jet streams can grab it and spread it around, which are levels where air travel happens. > If the US and Canada had taken the same tack as Europe not a plane > would have flown in North America from Mexico to the Arctic Circle, > for the duration of the several eruptions that took place. That > didn't happen. Flights were canceled only where they were at risk. Which is just what happened this time, too. It's just that this particular volcano provided more risk. The US and Canada have been extremely careful about routing air travel around some Alaskan volcano plumes, for example; we've just been fortunate that the ash plume is mostly in places where it can be routed around. (And the consequences of not routing around were discovered to be all four engines out and 747s don't glide so well...) -- Graydon -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
