PLT OF A PA34 SENECA IN IMC HAD BRIEF LOSS OF ACFT CTL APPARENTLY DUE TO WAKE TURB. GYROS TUMBLED AND HE RECEIVED A NO GYRO APCH.

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AT 6000 FT I WAS SKIMMING THE TOPS PROCEEDING DIRECT SAT VORTAC ON A 270 DEG HDG. I RECEIVED CLRNC TO 4000 FT. AT 5900 FT I WAS IN IMC. AT APPROX 5800 FT; I FLEW THROUGH THE FIRST OF 2 PERIODS OF SIMILAR VIOLENT CHOP THAT BEGAN AND ENDED SUDDENLY WITH SMOOTH AIR BTWN. I IMMEDIATELY FELT A G-FORCE SENSATION; AS IF I WAS IN A STEEP R BANK TRYING TO MAINTAIN ALT; AFTER I CAME THROUGH THE SECOND SERIES OF CHOP. BECAUSE OF OCCASIONAL BREAKS IN THE OVCST; THE GND LIGHTS APPEARED TO BE IN AN UNUSUAL POS. THIS WAS THE FIRST OF A SERIES OF QUICK AND SUDDEN UNUSUAL FLT ATTITUDES AS EVIDENCED BY INST INDICATIONS AND VISUAL REFS. BECAUSE OF THE SUDDEN OCCURRENCE OF THE UNUSUAL ATTITUDES I INSTANTLY ASSUMED THAT I HAD HAD A VACUUM FAILURE AND SUBSEQUENT ATTITUDE GYRO FAILURE. THEREFORE; SINCE I WAS IN IMC I DECLARED AN EMER. IT IS NOW MY BELIEF; BASED ON ALL EVENTS; INDICATIONS; AND MY EXPERIENCE THAT I FLEW THROUGH WAKE TURB WHICH CAUSED THE GYROS TO TUMBLE. THE 2 PERIODS OF TURB WERE VERY VIOLENT; JOLTING AND SYMMETRICAL AND COULD HAVE BEEN PRODUCED BY ONE OF THE SEVERAL PLANES FLYING AT SAT AT THAT TIME. THE SURROUNDING AIR WAS SMOOTH AND STABLE WHICH; AS I UNDERSTAND IT; WILL ALLOW WAKE VORTICES TO LINGER. AFTER STABILIZING THE ACFT AT 3000 FT; I WAS OFFERED AND ACCEPTED NO GYRO VECTORS TO THE ILS COURSE AND COMPLETED A PARTIAL PANEL APCH TO 100 FT ABOVE MINIMUMS WITH A SAFE LNDG. ALL EVENTS TOOK PLACE IN IMC SO I AM NOT SURE OF WHAT SPECIFIC ATTITUDES (FLT ATTITUDES) THE AIRPLANE WERE IN. NO TWR RPT WAS REQUIRED. NOTE: THERE WERE 2 GLIMPSES OF GND LIGHTS AND ONE OF THE SKY BECAUSE OF OVCST BREAKS DURING THE PERIOD OF UNUSUAL ATTITUDES BUT THEY DID NOT PROVIDE A VERY SURE MEANS OF KNOWING THE ATTITUDE OF THE AIRPLANE.