4dogs SH,Try FAR 25.335(d)...
Stay Alive
That's right 4dogs - same goes for smaller airplanes with FAR 23 (i.e. no
Vb there) although older aeroplanes of UK origin would have a flight envelope per the BCAR's. The basic problem is that people use that book for regulatory aspects of flight envelopes - it is fine for the physics only.
Same goes for Va - there is scope for the designer to choose something different than Vs x sqrt (n1)