On the other hand, does the A300 have a hydrolic backup? It's an older bird. Also EMP would not cause the noise heard on the cockpit recorders.
I don't think the A300 has backup hydraulics, but I'm not sure. What I remember is that the manufacturer touted the fact that it had redundant computer systems so that the failure of one or even two wouldn't cause a crash.
But if they all went out at once I think all the pilots could do is watch the view.