Yes, that's pretty much what my math came up with too. But for sure
I lost 2000' (I couldn't believe it when I looked at the altimeter after
recovering the plane - I'd been pretty focussed on the ASI since I
was close to redline). And I don't think the whole thing lasted more
than 10 seconds, although of course I wasn't timing it. Maybe it
was longer, but usually these things seem to last longer than they
really do, not less.

The terrain there is a bit special - there's a first ridgeline which is
at 6000-7500', then after a couple of miles there's a lower ridge
at around 4000', with a valley in between at about 2000'. I think
the only reason I recovered (much though I'd like to take credit for
my excellent airmanship :-) ) is that we flew through the downdraft.

I don't know whether this was "severe turbulence" according to
the definition. It was actually quite smooth, except that we were
going down at something around -1G. I did keep the plane under
control - my main concern being to avoid hitting Vne. We came out
about 30 degrees off heading. My wife says we did bank quite
steeply - she was looking out of the windshield, I was focussed on
the instruments. Whether it was "severe" or not, it was certainly quite
an experience, one I'm not in a big hurry to repeat.

John

"Mike Rapoport" wrote in message
ink.net...
Are you sure about those figures? If the acceleration was constant. 2000'
in 10 seconds is a vertical speed of zero increasing to 24,000fpm
(270mph+)
in five seconds and then back to zero in another five seconds. I have
never
heard of anything like it and certainly never experienced anything
similiar.

I have experienced vertical speeds of 5000fpm in mountan waves systems on
the east side of the Sierra near Minden, but those were with 100kt+ winds
at
ridge level (trees knocked down, semis turned over, planes beaking tie
down
ropes ect)

Mike
MU-2

"John Harper" wrote in message
news:1075704296.323452@sj-nntpcache-5...
Flying from Palo Alto to Santa Monica yesterday, we hit (I think) a
rotor
coming over the mountains north of LA. We'd had some fairly strong
up and downdrafts, though nothing really unpleasant, when suddenly
we were going DOWN - about 2000' in 10 seconds or so, everything
stuck to the roof for maybe 5-10 seconds. It was an interesting ride...
most things landed shortly afterwards (and I even found a flashlight
that
had disappeared) although my E6B remained lodged somewhere
and fell on my head on final.

Afterwards, my wife asked me how often this happens... once per
flying lifetime, much less, every few years. I couldn't answer... for
sure
the first time in my 600 hours, but that's not much.

So here's my informal sample... how many people here have had a
similar experience? Anyone care to guess how unlikely this it?

(And to forestall, or try to, the people who tell me I should know
something
about mountain flying, yes I HAVE read Sparky Iverson's book, and
anyway living in the Bay Area it's hard to go anywhere much without
overflying mountains. I was over 2000' above terrain too, 9500'
over a ridgeline at about 6000').

John