We show that the CR structure on the twistor space of a quaternionic contact
structure described by Biquard is normal if and only if the Ricci curvature of
the Biquard connection commutes with the endomorphisms in the quaternionic
structure of the contact distribution.Comment: 15pages, LaTeX2e, typos corrected, final version to appear in Quart.
J. Math. (Oxford
