A320 FLC EXPERIENCED UNKNOWN TURB AT MOD ENRTE TO SFO. RPTR BELIEVES IT WAS WAKE TURB CAUSED BY A PRECEDING ACFT. ATC AND TCASII DID NOT REVEAL TFC AHEAD OF THE FLT. RPTR SPECULATES IT HAD NOT DISSIPATED.

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DURING DSCNT INTO SFO (MOD 2 ARR) WE ENCOUNTERED POSSIBLE WAKE TURB. THE RIDE HAD BEEN SMOOTH PRIOR TO THIS AND THE CAPT HAD JUST ASKED ATC ABOUT RIDES AND WAS TOLD IT WAS SMOOTH SO THE SEAT BELT SIGN WAS OFF. PASSING FL190 THE ACFT PITCHED DOWN APPROX 5 DEGS AND ROLLED R APPROX 20 DEGS. THIS WAS FOLLOWED BY A SECOND BUMP ABOUT 10 SECONDS LATER. (THE CAPT GOT THE SEAT BELT SIGN BACK ON PRIOR TO THE SECOND BUMP.) THE FIRST FA NOTIFIED THE CAPT THAT 1 FA IN THE REAR HAD BEEN THROWN TO THE FLOOR AND MIGHT BE INJURED. AS HE DEALT WITH THE FA'S; I WAS FLYING THE APCH AND MAY HAVE DRIFTED L OF COURSE (QUIET BRIDGE VISUAL). ONCE ON THE GND; THE CAPT ELECTED TO HAVE EMT'S MEET US. WE WERE CLRED TO THE GATE 'BY ANY RTE' BY GND. AS I TALKED WITH THE COMPANY THE CAPT WAS TALKING WITH THE FIRST FA TRYING TO DETERMINE THE EXTENT OF POSSIBLE INJURIES. WE LATER FOUND OUT THAT GND HAD TRIED TO CALL US SEVERAL TIMES. THERE WERE NO PAX INJURIES. I CAN THINK OF NO ACTION WE COULD HAVE TAKEN TO PREVENT THIS OCCURRENCE; SINCE THE RIDE HAD BEEN SMOOTH PRIOR TO THIS AND RPTED SMOOTH AHEAD. GREATER ATTN ON MY PART WOULD HAVE RESULTED IN A BETTER APCH AND PERHAPS NOT MISSING GND'S CALL(S). CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN THE WAKE TURB CALLBACK QUESTIONNAIRE. CALLBACK CONVERSATION WITH RPTR ON ACN 364961 REVEALED THE FOLLOWING INFO: THIS RPTR WAS OCCUPYING THE R SEAT AS THE PIC WHILE HE WAS GIVING IOE IN THE A320 TO A NEW CAPT. THE FLT HAD BEEN VERY ROUGH WITH LIGHT TO MODERATE TURB FROM INITIAL CLB TO THE W SIDE OF THE SIERRA MOUNTAIN RANGE WHERE IT SUDDENLY BECAME VERY SMOOTH; ACCORDING TO THE RPTR. AS THEY STARTED THEIR DSCNT ON THE STAR; THE RPTR SAID THAT HE REQUESTED RIDE RPTS FROM THE ARTCC CTLR. HE HEARD THE CTLR TALK TO OTHER ACRS AHEAD OF HIM; BUT DOES NOT REMEMBER THEIR CALL SIGNS. THEY RPTED THEIR RIDES AS SMOOTH. JUST BEFORE HE ADJUSTED HIS TCASII'S RANGE TO 5 NM FOR THE APCH ENVIRONMENT; HE SAID THERE WAS AN ACFT 15-20 NM AHEAD. AT 19000 FT THE ACFT SUDDENLY ROLLED AND YAWED TO THE R ABOUT 20 DEGS OF ROLL AND ABOUT 10 DEGS OF YAW. THE STUDENT CAPT STARTED HIS RECOVERY BY DISCONNECTING THE AUTOPLT AND SMOOTHLY ROLLING TO WINGS LEVEL; THE RPTR SAID. HE ALSO SAID THAT HE RPTED THIS TO THE ARTCC CTLR. AT ABOUT THE SAME TIME THE RPTR PUT THE SEAT BELT SIGN ON AND MADE AN ANNOUNCEMENT THAT THE FLT ATTENDANTS SHOULD SIT DOWN IN THE NEAREST AVAILABLE SEAT IMMEDIATELY. SHORTLY AFTER THIS ANNOUNCEMENT; HE SAID; THEY HAD THE NEXT WAKE EVENT WHICH WAS A REPEAT OF THE PREVIOUS ENCOUNTER EXCEPT THAT THE AUTOPLT WAS ALREADY OFF FOR THIS ONE. AGAIN; HE SAID; THE RECOVERY WAS SMOOTH. HE THEN WAS CALLED BY THE LEAD FLT ATTENDANT WHO RPTED INJURIES TO ALL FLT ATTENDANTS WITH THE AFT FLT ATTENDANT THE MOST SEVERE. THE FLT ATTENDANTS WERE TAKEN TO THE HOSPITAL WHERE THE AFT FLT ATTENDANT REMAINED OVERNIGHT. ALL OF THEM ARE NOW RECOVERED AND ON THE LINE; ACCORDING TO THE RPTR. THE RPTR SAID THAT HE MET WITH FLT DEPT MGRS AND THEY WERE VERY INTERESTED IN THE INCIDENT. HE PARTICIPATED IN A CONFERENCE CALL TO ALL MGRS ABOUT THE PROB AND THE COMPANY HAS INCLUDED THIS INCIDENT IN THEIR TRAINING TAPES FOR RECURRENT GND SCHOOL.