WAKE ENCOUNTER -- A COMMUTER ACFT HITS THE WAKE OF A B767-200 AND RECOVERS; BUT CHANGES RWYS TO AVOID ANY FURTHER ENCOUNTERS.

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WE WERE APCHING THE PITTSBURG AREA AND ADVISED THAT WE WERE FOLLOWING A B767 5 MI AHEAD. THE CAPT AND I SPOTTED THE TFC AHEAD OF US. AT THE TIME WE WERE AT 6000 FT AND WERE QUESTIONING WHETHER WE WERE ACTUALLY 5 MI BEHIND THE B767. APCH CTL THEN INSTRUCTED US TO SLOW TO 180 KTS AND DSND TO 4000 FT. I WAS HESITANT TO START A DSCNT TO AN ALT BELOW THE B767. I STARTED A DSCNT; BUT THE CAPT AND I DECIDED TO LEVEL OFF AT 5000 FT AND START DOWN AGAIN ONCE I WAS A DOT ABOVE THE GS. UNFORTUNATELY; I DSNDED BELOW THE B767 AND AT ABOUT 10 MI OUT; WE ROLLED TO THE L ABOUT 20-30 DEGS. WE LANDED WITHOUT FURTHER INCIDENT ON RWY 28L. AFTER REVIEWING THE SIT; I SHOULD NOT HAVE ACCEPTED THE DSCNT CLRNC TO 4000 FT. WE DID NOT HAVE TCASII ON BOARD TO CONFIRM THE 5 MI DISTANCE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR WAS FLYING A BAE JETSTREAM 31 AND THE PRECEDING ACFT WAS A B767-200. THE FLC OF THE JETSTREAM COULD SEE THE PRECEDING ACFT; BUT THEY COULD NOT TELL ITS TYPE BECAUSE OF A BRIGHT SUNLIGHT REFLECTION FROM IT IN THE MORNING SUN. WHEN THE CTLR STARTED THE RPTR DOWN TO 4000 FT THE FLC ASKED ABOUT THE PRECEDING TYPE AND THEN THEY DECIDED TO SLOW THEIR DSCNT RATE IN AN ATTEMPT TO STAY ABOVE ANY POSSIBLE WAKE. THEY WERE AT 5000 FT BY NOW AND THEY HIT THE WAKE AS THEY WERE DISCUSSING THAT POSSIBILITY. THE ACFT WAS ONLY PARTIALLY CONTROLLABLE AND THE FO (FLYING) APPLIED A LARGE AMOUNT OF R RUDDER AND THE CAPT ADDED SOME R AILERON AND THE ACFT; AFTER SOME HESITATION; SLOWLY ROLLED WINGS LEVEL. THE RPTR SAID THAT THE CAPT DECIDED AFTER THE ENCOUNTER TO NOT FOLLOW THE B767-200 AND ORDERED A GAR. AS HE ADVANCED THE PWR THE CAPT INFORMED THE CTLR OF HIS DECISION AND THE CTLR OFFERED RWY 28R TO THEM AND THEY ACCEPTED PERFORMING A VISUAL APCH.