It is my understanding that the separation was adequate in terms of the required time or distance. The problem was initiated by the 747 making a wide turn out and the A-300 cutting across the inside of that turn. Had it not done so, but followed the same track as the 747 the better-performing two-holer would have been above the vortices of the 747 all the way.
And yes, it can be really really bad.
I've been rolled right square upside-down at about 600' on final into LAX
. I was flying a Cessna 402 at the time and the turbulence was caused by a 727. Had I known I was going to roll that far I'd have put aileron in the same direction and just gone a full roll. As it was I was fighting the roll all the way over and back.
A friend crashed in the wake of a 747. I looked at the wreckage of his Cessna 206 and I'm almost convinced that the left wing, strut, and door frame were coming off the plane before he hit the ground, torn off by the vortex. I might be wrong about this, but the wing and door frame were still a single unit with almost no other damage except having been ripped from the side of the Cessna.
Happiness is not seeing another trite Ste. Maarten photo all week long.