A B737-300 IN CRUISE AT FL330 DECLARED AN EMER AND DIVERTED DUE TO THE HORIZ STABILIZER TRIM FAILED IN ALL MODES CAUSED BY A FAILED JACKSCREW GEAR BOX ASSEMBLY.

Narrative

DURING CRUISE FLT AT FL330; THE AUTOPLT WAS HAVING DIFFICULTY MAINTAINING LEVEL FLT. ONCE THE AUTOPLT WAS UNCOUPLED; IT WAS DISCOVERED THAT THERE WAS NO NOSE DOWN TRIM. DISPATCH AND MAINT WAS RADIOED AND THE PROB WAS NOT ABLE TO BE RESOLVED. DEST WX WAS AT MINIMUMS WITH TSTMS AT THE FIELD. IT WAS DECIDED THAT BNA HAD THE BEST WX IN THE AREA SO AN EMER WAS DECLARED WITH ZTL AND WE WERE CLRED TO BNA. DURING THE DIVERSION; THE FLT ATTENDANTS WERE BRIEFED AND WERE TOLD TO PREP THE CABIN FOR AN EMER LNDG IN 20 MINS. DURING OUR DSCNT; THE ACFT WAS CONFIGURED EARLY FOR A CTLABILITY CHK; AT THAT TIME THE NOSE UP TRIM FAILED. A JAMMED STABILIZER LNDG CHKLIST WAS COMPLETED AND A NORMAL FLAPS 15 DEG APCH AND LNDG WAS ACCOMPLISHED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CREW FIRST NOTED THE ACFT HAD NO NOSE DOWN TRIM IN SPD TRIM; MAIN ELECTRIC TRIM AND MANUAL. THE RPTR SAID THE ACFT WAS A B737-300 AND THE TRIM OPERATED NORMALLY ON PREFLT CHK AND TKOF. THE RPTR SAID ON DSCNT THE ACFT WAS CONFIGURED FOR LNDG WITH GEAR AND FLAPS EXTENDED WHEN IT WAS NOTED THE NOSE UP TRIM ALSO FAILED IN ALL MODES. THE RPTR STATED THE LNDG WAS UNEVENTFUL. THE RPTR SAID MAINT RPTED THE FAILURE WAS IN THE JACKSCREW GEAR BOX WHICH WAS REPLACED.