Now we're getting somewhere!
So what you say is that Vmo is not just a margin to Vd or some sort of airframe buffet/flutter/undesirable handling characteristics etc? And if I understand you correctly, a B737, A319 or Lear Jet have wind shields that can withstand a bird strike at, say, 300KIAS? Then I wonder why the Q400 could not have been fitted with stronger windows? S'pose it would have been much more expensive? Or just that they use the same material as in the older series aircraft, which did not have the "luxury" of travelling at speeds greater than 250-ish anyway.
It would also be very interesting to have a look at the actual certification requirements. Is 8-10.000ft the official certifiation altitude limit when it comes to bird strike, or is it an altitude chosen by DeHavilland?
I'm just trying to understand the hows and whys, and get the full story behind this restriction. That way I can explain it to my colleagues as well, and thereby achieve compliance through knowledge. Or something to that effect
