Right - since flying a specific indicated altitude is nothing more than flying a line of constant pressure, I'd much rather fly into a warm High than a cold Low.
-p Cory Papenfuss wrote: >> > As a pilot, I've heard lots of other pilots questioning the > discrepancy between the altimeter and GPS. It's two main factors... the > difference between the mathematical model of the earth the GPS uses (not > spherical) being one, but the non-standard pressure lapse rate with > altitude. That's primarily due to non-standard temperature, but can be > affected by other things such as windshear with winds aloft. Of course > the GPS must also support manually entering the current barometric > altimeter setting or else the resulting barometric reading is crap. (e.g. > standard day is 29.92 inHg, but good-weather high might be 30.30 inHg) > > Pilots deal with this more often then most hikers since they > often fly higher than most hikers, and also fly through weather systems > (rather than hikers waiting for weather systems to pass them). > > One interesting tidbit that's taught to pilots in Alaska and > Canada but not in the rest of the US deals with cold-weather compass > errors. Consider a pilot beginning a long descent to an airport at low > elevation, but there's high terrain along the way. The colder the weather > is from standard (e.g. arctic conditions) and the higher the terrain is > above the airport, the more inaccurate the pressure altimeter is relative > to *true* (i.e. "not hitting the rocks") altitude shown on aeronautical > charts. Most of the times it's not an issue, but it can be under the > right circumstances. > > -Cory > -- 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.
