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Cactus521

freefall

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Can anyone tell me why airliners sometimes drop rapidly without warning? A friend told me recently that the plane he was on dropped suddenly over the Atlantic, with the people not weraing seatbelts ending up in adjascent seats. This happened twice within quite a short space of time and it scared him senseless.I'm not sure I'd have enjoyed it either?!!! *gulp*Is it a pressure thing or wind? Is it classed as a stall? Is it dangerous? Or quite a common/frequent occurence? I really know nothing about why this might happen.Curiously,Simon.

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It doesn'thappen too often fortunately, but it IS the reason why you always hear on any flight to 'please remain seated and keep your seatbelt on' as a preference, even after the 'safety belt sign' goes off.The phenomemen is usually caused by sudden down drafts ( I think that is the English word for it), i.e. air moving down with high speeds. This happens for instance when air from a cumulonimbus cloudhits you. In front of such clouds there is a good chance of heavy upwards and downwards air currents, caused by difference in temperature around and in such weather systems.I agree, it is not nice to be in an airliner when that happens, pretty scary, although this is not too dangerous as long as there is enough height.More dangerous are the microbursts that occur when the down draft hits the earth surface and causes a star pattern of very high turbulence. This is extrmely dangerous for landing or departing aircraft and airliner pilots get special training nowadays to recognize situations where this might occur. :-outta Francois :-wave[table border=0 cellpadding=10 cellspacing=0][tr][td valign=bottom" align="center]"At home in the wild"[/td][td valign=bottom" align="center][link:avsim.com/alaska/alaska_052.htm|Don's Alaskan Bush Charters]"Beavers Lead the Way"[/td][td valign=bottom" align="center][link:www.avsim.com/vfr_center/mainpages/vfr_flights_main_page.htm]VFR Flight Center]"Looking Good Outside"[/td][/tr][tr][td valign=top" align="center]http://bfu.avsim.net/sigpics/logo75b.gif[/td][td valign="top" align="left" colspan=2]http://www.fssupport.com/images/moose2.gif[/td][tr][/table]________________________Francois A. "Navman" DumasAssociate Editor &Forums AdministratorAVSIM Online![/bemail: fdumas@avsim.com________________________

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Thanks for the info, Francois. :)

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I've had, as many others too I'm sure, the same experience in a Cessna 150. We had rented a plane at Buttonville north of Toronto for a flight to Toronto City Centre (island airport) and back. Made it down to the island fine and upon departure, asked for clearance to do a lap around the CN tower. Somewhere in the last 3/4 of the lap, we were hit with a huge downdraft. This thing was so powerful and out of nowhere, if we hadn't had our seatbelts on we would have been flying the rest of the trip home open air style.CF-AOA

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I have encountered as a passenger such drops (coffee cup rising) in airliners crossing the Great Lakes in a path from New York to Minneapolis which crosses Buffalo NY when transitioning from over land to water. It was sunny with some scattered stuff above and below. Thermals can occur at land/water transitions as well as cloud effects due to sudden temperature variances over the different surfaces and the air currents caused by atmospheric attempts to neutralize pressure and density differences.It's fun to watch wings flap on a big airliner, but it cost me a white shirt.Anyway, if you monitor on-line aviation weather anywhere, look for pilot reports of turbulence, get the location, and check the observations in that area to get an idea of cause/effect.

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Just east of the Rockies, you always want to make sure you're in your seat with the seatbelt fastened. The same holds true if you're crossing the Sierras, especially between Bakersfield and Reno. I've been on several flights where we've hit the clear air chop, and have experienced some rather intense "freefalls". The worst (about 80 miles E of the Rockies) was eerily fascinating, because the beverage carts "floated" about a foot above the aisle, and in front of me I could see meal trays, cups, forks, & knives doing the same weightless "dance". No one was injured, but that aisle cleared out in nothing flat. I don't think anyone got up from their seats until we landed in MSP...The reason why this happens so often in mountain areas is due to the dynamics of the prevailing winds. They literally start rotating as they spill off of the lee side of the mountain range, and this can go up into the flight levels. That's why some of the most amazing sailplane records are set near Reno..... Catch the "up" side of these rotating winds, and you can ride a glider up into the flight levels.I'm less certain of the dynamics over the ocean. But I believe some of it has to do with the way the jet stream interacts with local wind currents. A sign of trouble....scattered lenticular clouds (I call them the "UFO" clouds since they take on that type of shape). I used to live in Gardnerville, NV, and ofter saw these clouds when the jet stream was nearly overhead.-John

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