Severe (or more) turbulence... how common?

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

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

But for sure
I lost 2000' (I couldn't believe it when I looked at the altimeter after
recovering the plane...

[...]

I don't know whether this was "severe turbulence" according to
the definition. [...] I did keep the plane under
control - my main concern being to avoid hitting Vne.


Unless you intended to lose 2000 feet, I'd say the plane was not under control.
The wings may have been level, but two thousand uncommanded feet of altitude
loss qualifies to me as severe turbulence. And whether it was smooth or not is
irrelevant - bumpy air is "chop", altitude deviations are "turbulence". Sort
of.

Jose

--
(for Email, make the obvious changes in my address)

Well, I was about to start descending, and it was quite handy to lose
2000', but I certainly wasn't planning to lose it THAT quickly!
In any case I reported it as severe turbulence at the time.

I forgot to mention that I had a 25kt tailwind - nothing remarkable -
at 9500'. It sped up to 40kt or so over the ridge, I was briefly
showing ground speed over 200kt.

John

"Teacherjh" wrote in message
...

But for sure
I lost 2000' (I couldn't believe it when I looked at the altimeter after
recovering the plane...

[...]

I don't know whether this was "severe turbulence" according to
the definition. [...] I did keep the plane under
control - my main concern being to avoid hitting Vne.


Unless you intended to lose 2000 feet, I'd say the plane was not under
control.
The wings may have been level, but two thousand uncommanded feet of
altitude
loss qualifies to me as severe turbulence. And whether it was smooth or
not is
irrelevant - bumpy air is "chop", altitude deviations are "turbulence".
Sort
of.

Jose

--
(for Email, make the obvious changes in my address)

Smooth air does not consitute turbulence, nor does an altitude
excursion in smooth air. Mountain wave often causes uncommanded
altitude excursions of substantial magnitude but the air is absolutely
smooth. That is not turbulence. The airplane is under control, it is
just in an air mass that is rising or descending faster than the
airplane has the performance to overcome.

In general turbulence is defined as the force you feel as you are
thrown against the seat belt. So, it isn't even light until you are
being tossed against the belt. Severe is where control of the
airplane is in doubt and there may well be some question as to whether
the airplane will hold together. It is truly no fun at all when you
get into a condition where you cannot cause the airplane to return to
wings level flight due to the frequency and violence of the
displacements that are occurring. You also may face the risk of being
rendered unconscious due to striking the ceiling of the cabin.

Fortunately, it is rare.

If I recall correctly, a severe turbulence encounter in a transport
category aircraft requires a full airframe inspection. It's a good
idea in an FAR 23/CAR 3 airplane as well as a good friend bent the
wings of his Meridian last summer while avoiding thunderstorms when he
encountered severe turbulence.

All the best,
Rick

(Teacherjh) wrote in message ...

But for sure
I lost 2000' (I couldn't believe it when I looked at the altimeter after
recovering the plane...

[...]

I don't know whether this was "severe turbulence" according to
the definition. [...] I did keep the plane under
control - my main concern being to avoid hitting Vne.


Unless you intended to lose 2000 feet, I'd say the plane was not under control.
The wings may have been level, but two thousand uncommanded feet of altitude
loss qualifies to me as severe turbulence. And whether it was smooth or not is
irrelevant - bumpy air is "chop", altitude deviations are "turbulence". Sort
of.

Jose

"John Harper" wrote in message
news:1075755778.686463@sj-nntpcache-5...
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


If its smooth, its not turbulence. When you are flying roughly
perpendicular to a ridgeline and encounter a rotor there is a very strong
updraft and then an equally strong downdraft (of course the order is
reversed if you are going the other way). The terrain sounds like a good
setup for a wave if the air is stable and the wind is perpendicular to the
ridges and increases with height.

The numbers don't really match up with the reported conditions. To get
2000' of altitude loss in 10 seconds would require winds of well over 100kts
since the vertical speed is going to average 120kts. If you are interested
in mountain waves you should read the book "Exploring the Monster" which is
about the Sierra Wave Project which studied the very powerful wave systems
on the east side of the Sierra Nevada near Bishop. The Owens Valley is an
ideal wave generator being 10,000' deep, perpendicular to the jetstream and
about one wavelength wide. Gliders regularly reach 40,000' there and in the
Carson Valley farther north.

Mike
MU-2