Turbulence penetration speed is related to max manoeuvring speed Va. However, instead of being the fastest you can go where the wing stalls prior to exceeding max load limit as a result of control mishandling, Vturb (
Vb?) allows for sudden wind gusts momentarily increasing the TAS or angle of attack. How strong a gust you ask? I'm not sure, but FAR25 probably has the answer.
So if you fly faster than
Vb, a sudden updraft or side-draft or whatever, may cause the aircraft to exceed max load limit / Vno / Mmo before the pilot can react. If you fly much slower though, a sudden patch of turbulence may cause you to reach low speed buffet.
Moral of the story: if you fly at
Vb, you will be protected from Vs on the one hand and max load limit on the other, from all but the most statistically improbable wind gusts.
All the above dates back to when I did ATPL's about three years ago, so all care and no responsibility eh?
cheers,
O8
[ 30 October 2001: Message edited by: Oktas8 ]