Narrative:

During cruise flight at FL330, the autoplt was having difficulty maintaining level flight. Once the autoplt was uncoupled, it was discovered that there was no nose down trim. Dispatch and maintenance was radioed and the problem was not able to be resolved. Destination WX was at minimums with thunderstorms at the field. It was decided that bna had the best WX in the area so an emergency was declared with ZTL and we were cleared to bna. During the diversion, the flight attendants were briefed and were told to prep the cabin for an emergency landing in 20 mins. During our descent, the aircraft was configured early for a ctlability check, at that time the nose up trim failed. A jammed stabilizer landing checklist was completed and a normal flaps 15 degree approach and landing was accomplished. Callback conversation with reporter revealed the following information: the reporter stated the crew first noted the aircraft had no nose down trim in speed trim, main electric trim and manual. The reporter said the aircraft was a B737-300 and the trim operated normally on preflight check and takeoff. The reporter said on descent the aircraft was configured for landing with gear and flaps extended when it was noted the nose up trim also failed in all modes. The reporter stated the landing was uneventful. The reporter said maintenance reported the failure was in the jackscrew gear box which was replaced.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.