A seneca descending into sat had an upset that is believed to be from wake turbulence. The upset caused both gyros to tumble.

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Attributes
ACN	420710
Time
Date	199811
Day	Wed
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : sat airport : sat
State Reference	TX
Altitude	msl bound lower : 3000 msl bound upper : 5800
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : sat
Operator	general aviation : personal
Make Model Name	PA-34-200 Seneca I
Operating Under FAR Part	Part 91
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	observation : passenger
Qualification	pilot : commercial pilot : instrument pilot : cfi
Experience	flight time last 90 days : 150 flight time total : 1300 flight time type : 120
ASRS Report	420710
Person 2
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Events
Anomaly	aircraft equipment problem : critical inflight encounter : weather other anomaly other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : regained aircraft control flight crew : declared emergency
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

At 6000 ft we were proceeding direct to sat VOR on a 270 degree heading. Approach cleared us to 4000 ft. We entered IMC at 5900 ft. At approximately 5800 ft we hit 2 short episodes of violent symmetrical jolts with smooth air in between. I was reading the approach plate for the ILS 12R when suddenly I felt the airplane was in a steep right bank. I looked up at the flight instruments and the attitude indicator confirmed this. The steep bank was the first one of several sudden unusual attitudes, which caused the gyros to tumble and consequently provided us with false instrument indications. Thinking we had had a vacuum failure, we declared an emergency. We stabilized the aircraft at 3000 ft and received no- gyro vectors to the ILS final approach course. The runway came in sight 200 ft above minimums and a safe landing was made. It is my belief, based on instrument and occasional visual references, the events as they happened and my experience that we had flown through (severe) wake turbulence, causing unusual aircraft attitudes and consequently tumbling of the gyro instruments.

Original NASA ASRS Text

Title: A SENECA DSNDING INTO SAT HAD AN UPSET THAT IS BELIEVED TO BE FROM WAKE TURB. THE UPSET CAUSED BOTH GYROS TO TUMBLE.

Narrative: AT 6000 FT WE WERE PROCEEDING DIRECT TO SAT VOR ON A 270 DEG HDG. APCH CLRED US TO 4000 FT. WE ENTERED IMC AT 5900 FT. AT APPROX 5800 FT WE HIT 2 SHORT EPISODES OF VIOLENT SYMMETRICAL JOLTS WITH SMOOTH AIR IN BTWN. I WAS READING THE APCH PLATE FOR THE ILS 12R WHEN SUDDENLY I FELT THE AIRPLANE WAS IN A STEEP R BANK. I LOOKED UP AT THE FLT INSTS AND THE ATTITUDE INDICATOR CONFIRMED THIS. THE STEEP BANK WAS THE FIRST ONE OF SEVERAL SUDDEN UNUSUAL ATTITUDES, WHICH CAUSED THE GYROS TO TUMBLE AND CONSEQUENTLY PROVIDED US WITH FALSE INST INDICATIONS. THINKING WE HAD HAD A VACUUM FAILURE, WE DECLARED AN EMER. WE STABILIZED THE ACFT AT 3000 FT AND RECEIVED NO- GYRO VECTORS TO THE ILS FINAL APCH COURSE. THE RWY CAME IN SIGHT 200 FT ABOVE MINIMUMS AND A SAFE LNDG WAS MADE. IT IS MY BELIEF, BASED ON INST AND OCCASIONAL VISUAL REFS, THE EVENTS AS THEY HAPPENED AND MY EXPERIENCE THAT WE HAD FLOWN THROUGH (SEVERE) WAKE TURB, CAUSING UNUSUAL ACFT ATTITUDES AND CONSEQUENTLY TUMBLING OF THE GYRO INSTS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.