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

"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

"John Harper" wrote in message news:1075704296.323452@sj-nntpcache-5...

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


I've had it twice in 15 yrs. (about 1900 flying hrs.).

The first was on my student dual X-C. It was windy, but we weren't
flying over any mountains or ridges. It was one big jolt and that was
it. My instructor had just undone his shoulder harness to retrieve
something from the back seat. His head slammed into the ceiling and
was a little disoriented for a few minutes. Both my hands and feet
left the controls when it hit. I had an interesting bruise from the
shoulder harness and on my shins where they hit the bottom of the
panel.

The second was coming out of a pass in the Alaska Range on the
leeward side. Winds aloft at the peaks were in the 40 Kt range and
there were standing lenticulars all over the place. I flew into a
rotor right about where it should have been. Not very smart and I
should have known better. The plane was uncontrollable in pitch and
roll for about 15 seconds.

John Galban=====N4BQ (PA28-180)

I flew from vegas to Ontario (in the LA basin) last wednesday, comming over the
mountains (ziggy 3 arrival) we had a 1000 FPM downdraft and on the approach to
ONT it was horrible. I couldnt stay on the ILS for nothing. We was bouncing all
over the place. The downdraft was not a problem because I had to decend from
12000 to 9200 anyways, but I did have to lead leveling off by about 500 ft.

I fly into the LA area all the time and that had to be the worst day so far. But
it was to be expected with the storms moving in and out.

John Harper wrote:

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

If you ever experience truely *severe* turbulence you will never have
any doubt as to what *severe* really means.

The air is not smooth, it is not just an uncommanded altitude
excursion. It is something to behold.

I only hit severe once and fortunately had slowed to Va. The plane
stalled in level flight at Va. That is one whale of a ride!

Now, I've been in moderate (things not secured tend to fly around the
cockpit) a good many times and it's not a lot of fun, but severe is
memorable.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com