SEVERE WAKE TURB.

Narrative

ON DEC/SAT/94 I WAS RETURNING TO THE OAK ARPT FR OM A CURRENCY/PLEASURE FLT IN MY CESSNA 182 SKYLANE. AT APPROX 27 NM DME NW OF THE ARPT; I CONTACTED BAY APCH. I ADVISED I WAS VFR AT 3500 FT BUT REQUESTED AN IFR CLRNC TO EXECUTE THE ILS 27R APCH AT OAK. OAK WAS RPTING 2700 FT OVCST; 15 MI VISIBILITY AND LIGHT RAIN SHOWERS. WX TO THE NW OF THE FIELD WAS 6000 FT VFR; A SLOW-MOVING FRONT WAS ENTERING THE BAY AREA. BAY APCH INITIALLY PROVIDED ME A 140 DEG HDG AND ASKED IF I COULD MAINTAIN VFR. I ADVISED THAT I COULD BUT WOULD SOON NEED THE IFR CLRNC CLOSER IN AT 3500 FT. THE CTLR SHORTLY THEREAFTER ADVISED ME TO CLB AND MAINTAIN 4000 FT; AND THAT I WAS CLRED TO THE OAK ARPT VIA RADAR VECTORS FOR THE ILS RWY 24R. APPROX 8-10 MI N OF THE ARPT; THE CTLR ADVISED OF XING TFC; A HVY 747. I ADVISED I WAS IMC; AND NO CONTACT. I THEN SAW THE B747 EMERGE FROM A LAYER AHEAD AND TO MY L. I REQUESTED AN IMMEDIATE VECTOR FOR WAKE TURB. BAY TRACON ADVISED ME TO 'TURN R TO 140 DEGS.' AFTER A PERIOD OF TIME (PROBABLY ABOUT 1 MIN); TRACON ADVISED ME TO 'TURN L TO 100 DEGS.' SHORTLY AFTER COMPLETING THE HDG CHANGE; I FLEW THROUGH WHAT I BELIEVE WAS WAKE TURB FROM THE B747. MY ACFT WAS STRONGLY JOLTED CAUSING APCH PLATE BINDERS TO BE LIFTED FROM THE CTR CONSOLE BTWN THE 2 FRONT SEATS AND DEPOSITED IN THE BACK SEAT. OTHER PIECES OF PLT EQUIP (FLASHLIGHTS; SECTIONAL CHARTS; A HAND-HELD GPS; PENS; ETC) WERE THROWN ABOUT THE CABIN. I RECEIVED A BRUISE TO MY L UPPER THIGH FROM THE SEAT BELT; AND A STRAIN TO MY LOWER BACK. I WOULD CHARACTERIZE THIS TURB AS SEVERE; AS CTL OF THE ACFT WAS MOMENTARILY LOST. I BROUGHT THIS ACFT BACK TO STRAIGHT AND LEVEL AND TURNED R TO AVOID WHAT I THOUGHT COULD POTENTIALLY BE MORE TURB FROM THE OTHER WINGTIP. I THEN ADVISED BAY TRACON OF WHAT HAPPENED. BREAKING INTO AN AREA OF VFR WX I CANCELED MY IFR CLRNC; DSNDED AND LANDED AT OAK. NO DAMAGE TO THE ACFT WAS EVIDENT. I CONTACTED BAY TRACON AFTER LNDG. THE SUPVR ADVISED ME THAT THE XING TFC HAD BEEN A 747-400; HEAVILY LOADED FOR ITS NON-STOP SFO-LONDON FLT. SHE ADVISED THAT I HAD CROSSED BEHIND THE B747; BUT COULD NOT TELL ME HOW FAR. I WOULD SUGGEST THAT APPROPRIATE AUTH DETERMINE WHAT IS A SAFE XING DISTANCE BTWN LIGHT ACFT AND SUCH HVY ACFT AND ATC BE AWARE OF THE SIGNIFICANCE OF ALLOWING THESE TYPES OF ACFT TO COME TOO CLOSE. I HAVE BEEN A PLT FOR 21 YRS; FLYING LIGHT ACFT; HELIS THROUGH BUSINESS JETS. I HAVE NEVER HAD AN EXPERIENCE LIKE THIS.