using DiffEquation can transform to diff sys, but if convert back to transfer function, How is it?
with(DynamicSystems):
sys2 := DiffEquation(sqrt(1-a^2)/(1-a/s));
PrintSystem(sys2);
de := [Diff(x1(t),t) = a*x1(t)+a*u1(t), y1(t) = sqrt(1-a^2)*x1(t)+sqrt(1-a^2)*u1(t)];