Originally Posted by
LarryJ
The categories have not changed in many decades.
In reporting turbulence, it is usually classed as light, moderate, severe or extreme. The degree is determined by the nature of the initiating agency and by the degree of stability of the air.
Light turbulence momentarily causes slight changes in altitude and/or attitude or a slight bumpiness. Occupants of the airplane may feel a slight strain against their seat belts.
Moderate turbulence is similar to light turbulence but somewhat more intense. There is, however, no loss of control of the airplane. Occupants will feel a definite strain against their seat belts and unsecured objects will be dislodged.
Severe turbulence causes large and abrupt changes in altitude and/or attitude and, usually, large variations in indicated airspeed. The airplane may momentarily be out of control. Occupants of the airplane will be forced violently against their seat belts.
In extreme turbulence, the airplane is tossed violently about and is impossible to control. It may cause structural damage.
Light or moderate intensities can be further defined as either turbulence or chop. Chop is a type of turbulence that causes rapid and somewhat rhythmic bumpiness and is not as uncomfortable nor disruptive to activities as turbulence of the same intensity. We do not communicate the distinction between chop and turbulence with the flight attendants.
I don't doubt that the definitions are the same as always, but in my experience the FAs use a stronger term than is warranted quite often when describing turbulence. Just as when they say "final approach" when they mean "initial approach" or even "initial descent".
But I think there is also a change in expectation all around. Still air is much more reliably identified and found than in years past. A smooth flight used to mean one where the rumblings of the aircraft were not too bad, now it means when they are indistinguishable from sitting in your living room. As a passenger, I do appreciate that advance in knowledge and its application. But, again in my experience, because the nominal condition has been improved so much, the interpretation of terms used to describe turbulence have been rescaled downwards. I would speculate that one of the reasons for this is that the terms are subjective descriptions even in the official definitions, rather than quantitative thresholds of vibration.