The French crash was during take off:

http://en.wikipedia.org/wiki/Air_France_Flight_4590

it is rumoured that the Tu-144 crash at the Paris airshow was caused by the pilot overiding the flight control system to make a sharper turn,the g-forces pulled the plane apart..

But my guess is with the French recon plane,i saw a documentary about that and its seems the most viable cause..

they probably came to some sort of agreement not to inform the public,as both countries were embarrased.