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