On touchdown the aircraft ‘porpoised’, initially nose down, due to contact with the heels of the skids followed almost immediately by the cyclic being displaced fully aft and a progressive left (lateral) cyclic displacement. The cyclic was then centralised longitudinally as the aircraft pitched up before it was again displaced fully aft, on this occasion for a protracted period, out of phase with the oscillation in pitch attitude. The pitch oscillation continued (albeit to a lesser extent) and whilst full aft cyclic was maintained, the collective was lowered fully causing the disc attitude to be such that the MRB struck the tail. There was a subsequent violent roll of the airframe, before a full cessation of movement; this is assessed to be as a consequence of the impact forces.