BE76 ACFT IN CRUISE ON VFR FLT PLAN ON FLT FOLLOWING BY BUR TRACON ENCOUNTERED WAKE TURB FROM ARRIVING B737-300 ACFT DSNDING FOR APCH INTO BUR. THE B737 WAS 3 MI IN FRONT OF RPTR ACFT; YET THE WAKE WAS SEVERE ENOUGH TO CAUSE TEMPORARY LOSS OF CTL.

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APPROX 5 MI (NM) W OF VAN NUYS ARPT BE76 ENCOUNTERED THE WAKE TURB OF A DSNDING B737. THE BE76 WAS BEGINNING A VFR DSCNT FOR THE LAX SPECIAL FLT RULES AREA AND WAS AT 5000 FT MSL WHEN THE EVENT OCCURRED. THE BE76 HAD VISUAL CONTACT WITH THE B737 AS THE B737 DSNDED FROM 8000 FT MSL TO INTERCEPT THE BURBANK RWY 8 LOC. THE B737 CAME FROM THE L OF THE BE76 AND LEVELED OFF MOMENTARILY AT 5000 FT MSL IN FRONT OF THE BE76 JUST AS THE BE76 BEGAN A TURN TO THE SE FOR THE CORRIDOR OVER LAX. UPON ENCOUNTERING THE B737'S WAKE; THE BE76 ENTERED AN UNCOMMANDED 90 DEG BANK L TURN AND 30 DEG NOSE DOWN ANGLE. THE STUDENT RETARDED THE THROTTLES TO 14 INCH MANIFOLD PRESSURE BUT (NEITHER PLT) WAS ABLE TO RECOVER CTL OF THE AIRPLANE FOR APPROX 4 SECONDS. NO DAMAGE VISIBLE TO AIRPLANE; NO INJURIES TO CREW. WAKE TURB WAS NOT CONSIDERED TO BE A FACTOR AND NO ADVISORY WAS GIVEN FROM SOCAL. HOWEVER IT WAS ENCOUNTERED ABOVE THE FLT PATH OF A GENERATING AIRPLANE...IT CAN HAPPEN ANYWHERE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CALLBACK IN CONJUNCTION WITH THE WAKE TURB INCIDENT CALLBACK QUESTIONNAIRE. RPTR INSTRUCTOR PLT BELIEVES THE B737 WAS A -300 MODEL BECAUSE OF THE LARGE ENGS. WHEN THEY LOST CTL OF THE ACFT AND DSNDED APPROX 700 FT AND WHEN ASKED IF ATC COMMENTED ON THE ALT LOSS; RPTR SAID THAT THEY HAD JUST REQUESTED A DSCNT SO THE CTLR WOULDN'T NOTICE. RPTR AND HIS STUDENT WERE SHOCKED BY THE SEVERITY OF THE WAKE AND ESPECIALLY SINCE THE B737 WAS SO FAR AWAY; 3 MI.