A very interesting question, and I have to confess that despite having working in this area for about 10 years, I haven't the foggiest. For the benefit of others, the diagram in question is <A HREF="http://www.jaa.nl/jar/ihs_data/frameset.html?../av_vault/46000/46480/46480.htm" TARGET=_blank>here[/url.
And the JAA definition of airspeeds is [url=http://www.jaa.nl/jar/ihs_data/frameset.html?../av_vault/46000/46481/46481.htm]here</A>
I'm used to Va not being Vs*N1^½ - that is fairly common in more aeroelastic airframes. But in that case it is still at point A.
25.335 clearly says that: -
Va may not be less than VS1 n
, which I think is a typo on the JAA website and means Vs1*n^½, since it certainly isn't a linear relationship. n in this case is the limit load factor at Vc, known to most of us as N1. This makes sense to me, since in my experience, aeroelastic effects leading to a non-square-root stall curve, are generally in a sense that gives a higher Va, never lower.
However it also says that:-
Va need not be more than VC or the speed at which the positive CNmax curve intersects the positive manoeuvre load factor line, whichever is less
Which indicates that Va may at a speed below point A.
So, in summary. I haven't the faintest idea. Perhaps the diagram is a hangover from some previous requirement?
Anybody else got a clue?
G