CE560XL CITATION FLT CREW HAS A 'STABILIZER MISTRIM COMPARISON' AND 'AUTOPLT PITCH MISTRIM' LIGHTS ALONG WITH A 'MASTER CAUTION' LIGHT. FLT CREW PERFORMS THE EMER PROCS AND RETURNS TO LAND.

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UPON CLBOUT FROM RNO ON THE MUSTANG6 DEP; PASSING THROUGH 14500 FT; WE HAD A 'STABILIZER MIS-COMPARISON' AND 'AUTOPLT PITCH MIS-TRIM' MASTER CAUTION LIGHTS ILLUMINATE AND THEN EXTINGUISH. THE AUTOPLT WAS FLYING THE ACFT. WHEN THE LIGHTS ILLUMINATED; I LOOKED OVER AT THE ACFT PITCH TRIM INDICATOR AND SAW THAT THE ACFT WAS TRIMMED FULL NOSE DOWN. I DISCONNECTED THE AUTOPLT AND TOLD THE PIC THAT I WAS GETTING A VIBRATION IN THE CTL COLUMN. THE PIC THEN RAN THE 'STABILIZER MIS-COMPARISON' EMER CHKLIST. ONE STEP IN THE CHKLIST STATES TO REDUCE SPD TO BELOW 200 KTS. THE ACFT WAS INDICATING APPROX 230 KTS AT THIS POINT. AS I SLOWED THE ACFT BELOW 200 KTS; THE 'STABILIZER MIS-COMPARISON' LIGHT FLASHED ON AND OFF AND THE ACFT STARTED PITCHING DOWN. IT TOOK FULL AFT YOKE TO ARREST THE DSCNT. I INFORMED THE PIC THAT I WAS HAVING DIFFICULTY CTLING THE ACFT AND THAT WE NEEDED TO DECLARE AN EMER AND RETURN TO RNO IMMEDIATELY. AFTER SEVERAL SECONDS; I WAS ABLE TO RETRIM THE ACFT TO LEVEL FLT. THE PIC THEN CONTACTED ONE OF OUR CHIEF PLTS VIA THE ACFT FLT PHONE AND LET HIM KNOW THAT WE WERE RETURNING TO RNO AND THAT WE INTENDED TO DO A NO-FLAP LNDG AS WE DID NOT WANT TO CHANGE THE CONFIGN OF THE ACFT. DURING THIS TIME; I INFORMED THE PIC THAT THE CTLS FELT 'MUSHY' AND I AGREED THAT A NO-FLAP LNDG WAS THE BEST COURSE OF ACTION. WE LANDED UNEVENTFULLY AND UPON INSPECTING THE ACFT AFTER LNDG; WE NOTICED NO DAMAGE AND NOTHING OUT OF THE ORDINARY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR INDICATED THAT THEY PERFORMED THE QRH CHKLIST PROCS AND THE TRIM AND AUTOPLT MALFUNCTION WAS CLRED. HOWEVER; HE INDICATED THAT THERE APPEARED TO BE A VIBRATION AND THAT THE FLT CREW ELECTED TO NOT CHANGE THE CONFIGN OF THE ACFT AND TO PERFORM A 'NO FLAP' LNDG BACK AT THEIR DEP ARPT. POSTFLT INVESTIGATION REVEALED NO PROBS WITH THE ACFT. RPTR INDICATED THAT THEY WERE NOT SURE IF THERE WAS ANYTHING WRONG WITH THE ACFT.