FLC OF A FOKKER 100 WHILE ON FINAL APCH TO DCA EXPERIENCED A STABILIZER TRIM PROB. ACFT WENT TO FULL NOSE DOWN TRIM WHEN THE #1 AUTOPLT WAS DISCONNECTED; AND THEN ACFT WENT INTO A FULL NOSE UP TRIM CONDITION. FLC DECLARED EMER; EXECUTED A MISSED APCH AND DIVERTED TO IAD.

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IN A DSCNT FROM 4000 FT TO 3000 FT; SLOWING TO 180 KTS; FLAPS 8 DEGS; CLRED FOR THE MOUNT VERNON VISUAL RWY 36 AT DCA. TURNING BASE; I DISCONNECTED THE #1 AUTOPLT TO HAND FLY THE APCH. I IMMEDIATELY FELT A HVY NOSE DOWN FORCE ON THE CTL COLUMN. USE OF MY TRIM SWITCH ON THE YOKE HAD NO EFFECT. I GLANCED AT THE TRIM INDICATOR AND NOTICED FULL NOSE DOWN TRIM. I CALLED FOR FLAPS 15 DEGS; GEAR DOWN; AND THE ACFT RESPONDED POSITIVELY. WE WERE HIGH ON THE DSCNT PROFILE; SO I CALLED FOR FLAPS 25 DEGS. THE ACFT RESPONDED POSITIVELY AND I FELT CTL RETURNING. THE STABILIZER TRIM THEN RAN FROM A FULL NOSE DOWN CONDITION TO FULL NOSE UP. THE DECISION WAS MADE TO GAR. I GOT THE GEAR UP AND BOTH THE FO AND I HAD THE YOKE HELD FORWARD ALL THE WAY TO THE STOP. AT THAT POINT THE #1 AND #2 STABILIZER TRIM FAILURE MESSAGES CAME UP ON THE MFDU. THE FO RAN THE PROC AND ACCOMPLISHED THE ITEMS. IN THE MEANTIME I'M FIGHTING AN ACFT IN A FULL NOSE UP TRIM CONFIGN; 145 KTS OF AIRSPD; MAINTAINING FLT JUST BARELY. THE FO STATED TO ME THAT HE ALSO HAD HEARD THE CALVARY CHARGE BLARING AND HAD DISCONNECTED THE AUTOPLT DISCONNECT BAR. I CAN'T CONFIRM THIS AS I WAS BUSY AT THE TIME TRYING TO MAINTAIN SOME CTL AND AVOIDING THE WASHINGTON MONUMENT ETC. AS SOON AS THE STABILIZER TRIM SWITCHES ON THE FLT AUGMENTATION PANEL WERE TURNED OFF; THE STABILIZER TRIM RAN RAPIDLY BACK TO 1 UNIT NOSE UP AND STAYED THERE. I GOT THE PWR IN; AUTOTHROTTLES DISCONNECTED; AND GRADUALLY NURSED THE PWR AND PITCH TO SOME SEMBLANCE OF LEVEL FLT. WE RETRACTED THE FLAPS TO 15 DEGS. WE DECLARED AN EMER AND REQUESTED VECTORS TO IAD WITH A LONGER RWY. I FLEW FINAL APCH WITH 25 DEGS FLAPS AT 180 KTS AND LANDED UNEVENTFULLY. BECAUSE OF OUR SIT AT THE TIME I DO NOT KNOW IF WE OVERFLEW THE RESTR AREA NEAR THE MONUMENTS; CAPITOL; ETC. THAT WAS THE LEAST OF OUR PROBS AT THAT TIME. I WOULD LIKE TO COMMEND THE FO FOR HIS PROFESSIONALISM IN THE COCKPIT DURING AN EXTREMELY STRESSFUL AND CRITICAL TIME. I WOULD ALSO LIKE TO COMMEND FLT ATTENDANTS X AND Y FOR THE PROFESSIONAL WAY THEY CARRIED OUT THEIR DUTIES -- CALMING THE PAX AND PREPARING THEM FOR AN EMER LNDG DURING THIS EMER.