AIRFRAME ICE ON THE HORIZ STABILIZER CAUSES SERIOUS VIBRATION AND JEOPARDIZES ACFT CONTROLLABILITY.

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WHILE ON THE GND IN TVC THE ACFT WAS VISUALLY CHKED FOR ICE ACCUMULATION AND NONE WAS RPTED. THROUGHOUT DEP AND CRUISE; ACFT WAS CLEAN AND ON TOP THERE WAS AN OVCST WHERE IT WAS CLR ABOVE. UPON DSCNT INTO MQT THE ACFT ENTERED THE CLOUDS AT 5000 FT MSL. ALL ANTI-ICING AND DE- ICING EQUIP WAS SELECTED ON AND OPERATING NORMALLY. ONCE ENTERING THE CLOUDS MODERATE RIME ICE WAS ENCOUNTERED AND RPTED TO SAWYER APCH. WE WERE CLRED TO 3600 FT MSL AND WERE BEING VECTORED FOR THE ILS TO RWY 8 APCH. AIRFRAME DE-ICING WAS REMOVING THE RIME ICE AS IT WAS BUILDING AND ALL SYS WERE OPERATING. PRIOR TO FINAL APCH FIX THE ACFT WAS CONFIGURED TO LAND. THE CREW DID NOTICE A TEMP INVERSION ALOFT; BUT ICING REMAINED MODERATE AND WAS BEING SHED BY DE-ICING BOOTS. UPON REACHING 2200 FT MSL ON THE LOC AND GS THE ACFT YAWED L AND THE BALL DEFLECTED TO THE R. THE CAPT CONFIRMED NO PWR WAS LOST AND QUESTIONED THE FO ON HOW THE ACFT WAS HANDLING. AT THIS POINT THE TAIL SECTION SHOOK EXCESSIVELY AND THE ACFT FELT AS IF IT WERE STARTING A ROLL TO THE R. THE CREW EXECUTED AN IMMEDIATE GAR AND KEPT THE ACFT TO ITS PRESENT CONFIGN. WE ESTABLISHED A POSITIVE RATE OF CLB AT 135 KTS ON RWY HDG; AND A CLB RATE OF 1500 FT. ONCE WE ESTABLISHED ALT THE FLAPS WERE SELECTED TO 15 DEGS AND A NORMAL CLB WAS PERFORMED. FLT DIVERTED TO GRB WHERE A NORMAL APCH AND LNDG WAS MADE. UPON VISUAL INSPECTION OF THE ACFT. CLR ICE WAS VISIBLE ON ALL AIRFOILS AND RIME ICE ON ALL UNPROTECTED AREAS. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: RPTR ADDED THAT HIS CARRIER HAS HAD ABOUT 6 CASES OF SEVERE TAIL ICING THAT HE IS AWARE OF. SOME OF IT HAS BEEN GAP SEAL ICING AND NOT A SIMILAR PROB TO THIS ONE. HE DESCRIBED THE TAIL SHAKE AS IN ALL AXES. HE SAID THE PEOPLE SITTING IN THE TAIL GOT A VERY INTERESTING RIDE. HE SAID THEY RETRACTED THE FLAPS FROM 30 DEGS TO 15 DEGS AFTER THEY HAD ESTABLISHED THE CLB. HE CHOSE TO DIVERT TO GRB RATHER THAN TVC BECAUSE HE DID NOT WANT TO CROSS LAKE MICHIGAN WITH THE AIRPLANE FLYING THE WAY IT WAS. HE SAID THAT THE SHAKING DIMINISHED AS THE FLAPS WERE RAISED BUT NEVER COMPLETELY STOPPED. SUPPLEMENTAL INFORMATION FROM ACN 259289: AT 600 FT AGL; WITH APCH STABILIZED AND AT A SPD OF 135-140 KIAS (VAPP PLUS 15-20 KIAS); CAPT STATED A QUESTION REGARDING YAW DAMPENER. AT THE SAME TIME; I HAD NOTICED A 'SETTLING FEELING' AND MOVED THE PWR TO 55 PERCENT TORQUE (FROM 35 PERCENT) TO COMPENSATE. TAIL BEGAN SHAKING CTL YOKE IN RHYTHMIC PULSES AT APPROX 1/2 RATE OF STICK SHAKER. INITIATED GAR; ESTABLISHED CLB AT PLUS 7 DEGS PITCH; 135 KIAS; PLUS 1500 FPM. SHAKING CONTINUED THROUGHOUT CLB AND OVERSPD SOUNDED CONTINUOUSLY EVEN THOUGH WE WERE 15 KTS BELOW WHERE IT SHOULD HAVE SOUNDED. CONTINUED CLB TO ABOVE CLOUD DECK. ACCELERATED AND RAISED FLAPS.