FLC EXPERIENCES UNCOMMANDED ROLL AND PITCH DOWN.

Narrative

AT FLAPS 5 DEGS AND 180 KTS; WE EXPERIENCED A STRONG AIRFRAME VIBRATION. SHORTLY THEREAFTER THE ACFT BEGAN AN UNCOMMANDED ROLL TO THE R WITH BANK ANGLES EXCEEDING 30 DEGS. FULL OPPOSITE CTL WHEEL INPUT HAD NO IMMEDIATE EFFECT ON DECREASING ROLL RATE. IT WAS MY PERCEPTION THAT THE ACFT WAS GOING TO CONTINUE ROLLING OVER ONTO ITS BACK. A SHORT TIME LATER I WAS ABLE TO REGAIN CTL OF THE ACFT. THE AUTOPLT WAS THEN ENGAGED BUT STRONG VIBRATION CONTINUED. SHORTLY AFTER THE AUTOPLT WAS DISENGAGED; THE ACFT WENT INTO AN ABRUPT 10 DEG DIVE AND FULL AFT CTL WHEEL POS HAD NO EFFECT. AT THIS POINT NO ONE ON BOARD BELIEVED WE WERE GOING TO RECOVER. EVENTUALLY THE CTLS TOOK EFFECT AND A NORMAL PITCH ATTITUDE WAS ATTAINED. AN EMER WAS DECLARED AND LNDG WAS UNEVENTFUL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT DURING THE PITCH DOWN THE COPLT NOTICED THE STABILIZER TRIM WAS NOT MOVING BUT HEARD A GRINDING NOISE COMING FROM THE THROTTLE QUADRANT. AFTER THE FLT LANDED; A TEST FLT WAS ACCOMPLISHED WHICH WAS NORMAL EXCEPT THE COPLT NOTICED METAL SHAVINGS COMING FROM THE CTL QUADRANT. ON TAXI IN FROM THE TEST FLT; THE SPOILER HANDLE WOULD NOT STOW AND AN INSPECTION REVEALED SEVERAL BEARINGS IN THE STABILIZER TRIM FOLLOW UP SYS FAILED. A TIE ROD AND A DRIVE GEAR. THE RPTR STATED HE DID NOT BELIEVE THE COMPANY POS THAT HIS EXPERIENCE WAS RELATED TO THE WAKE OF A PREVIOUSLY LANDED DC-8 AND A BOEING 757 WHICH LANDED AHEAD OF THE DC-8. THE ROLL WAS SO SLOW AND PERSISTENT THE FLC THOUGHT THEY WERE GOING TO ROLL OVER ON THEIR BACK. THEN THE PITCH OVER WAS SO SLOW AND PERSISTENT THEY THOUGHT THEY WERE GOING TO HIT THE GND. BOTH MOTIONS WERE OPPOSED BY FULL CTL INPUTS AND SECONDS WENT BY BEFORE THE AIRPLANE SHOWED ANY TENDENCY TO RESPOND TO BOTH ROLL AND PITCH.