EMB145 FO REPORTS RUDDER SYSTEM FAILURE DURING CLIMB RENDERING AUTOPILOT AND YAW DAMPER INOPERATIVE. ACFT IS HAND FLOWN TO DESTINATION AT FL280.

Narrative

AT 12000 FT WITH THE AUTOPLT ON IN FLC MODE THE ACFT STARTED TO PITCH UP AND DOWN TO CHASE THE 270 KT AIRSPD. SO; I SWITCHED TO VERT SPD MODE ON THE FCP AND SELECTED THE CORRECT VERT SPD FOR 270 IAS. I WAS TRYING TO SMOOTH OUT THE CLB ATTITUDE FOR PAX COMFORT. AT 13000 FT MSL THE AURAL 'AUTOPLT; AUTOPLT' SOUNDED. THERE WERE 3 EICAS MESSAGES: AUTOPLT FAIL (RED); RUDDER SYS 1-2 INOP (AMBER) YAW DAM FAIL (AMBER). I DID HAVE MY HANDS ON THE CTLS AND RESUMED CTL OF THE ACFT UNDER HAND FLYING CONDITIONS. THE ACFT WAS TRIMMED AND IN A GOOD PITCH ATTITUDE; NO ROLL CONDITION FOR THE CLB CONFIGN. I FLEW THE ACFT TO CRUISE ALT WHILE CAPT REVIEWED THE AOM AND CALLED MAINT CTL AND DISPATCH. I WORKED THE RADIOS AND FLEW THE ACFT TO A CRUISE ALT OF 28000 FT MSL. WE WERE NOT RVSM EQUIPPED BECAUSE THE AUTOPLT FAILURE SO I CHANGED OUR SUFFIX AND TOOK 28000 FT FOR DIRECTION OF FLT. THE CAPT DID DECLARE AN EMER BECAUSE OF THE LOSS OF A FLT CTL SYS. THE REST OF THE FLT WAS UNEVENTFUL. THE REASON FOR THE AUTOPLT FAILURE IS STILL UNKNOWN TO ME AT THIS TIME.