  We investigate the Fefferman spaces of conformal type which are induced, via
parabolic geometry, by the quaternionic contact (qc) manifolds introduced by
O.Biquard. Equivalent characterizations of these spaces are proved: as
conformal manifolds with symplectic conformal holonomy of the appropriate
signature; as pseudo-Riemannian manifolds admitting conformal Killing fields
satisfying a conformally invariant system of conditions analog to G. Sparling's
criteria; and as the total space of a SO(3)- or $S^3$-bundle over a qc manifold
with the conformally equivalent metrics defined directly by Biquard. Global as
well as local results are acquired.
