Strange Vmo limits.
This was discussed a while ago, but there was no conclusive answer. So...
On the BAe ATP (and on other turboprops) the Vmo curve has strange "breaks" in the curve at certain altitudes. The following is from the ATP:
SL ---> 15.000' - @SL, 227kts then increases linearly up to 230 at 15.000.
15.000'--->22.000' - at/above 15.000 it has suddenly reduced to 220 then it increases to 221 @ 22.000'
22.000'--->25.000 (max) - decreases linearly from 221 at 22.000' to 208 at 25.000'
Anyone able to explain why? If it has to do with Mcrit due to the thick wings - why then the (sudden) decrease followed by an increase. And why the sudden "break" at 15.000'?