CLR AIR TURB -- ACR HITS SEVERE CLEAR AIR TURB AND PAX ARE INJURED.

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CRUISING ALONG AT FL330; SMOOTH; VMC NIGHT TIME CONDITIONS; STARS VISIBLE ABOVE; OVCST LAYER BELOW; COCKPIT LIGHTING DARK; RADAR OFF; SEAT BELT SIGN OFF; 90 KT TAILWIND; HORIZON IN SIGHT. CAPT MADE A POS RPT OVERHEAD CALMA TO TOKYO RADIO ON HF. THEY COPIED AND TOLD US AN ACR FLT 200 MI AHEAD OF US HAD RPTED MODERATE- SEVERE CLR AIR TURB (CAT). ABOUT THE SAME TIME I WAS MONITORING INTERPLANE FREQ 128.95 AND HEARD ANOTHER ACR (AHEAD OF US AT FL350) CONTACT ITS SISTER FLT (COMPANY) TO WARN THEM THAT THEY HAD ENCOUNTERED TURB LIKE 'FALLING OFF A CLIFF.' I TOLD THE CAPT AND HE IMMEDIATELY NOTIFIED THE CHIEF PURSER OF POSSIBLE TURB AHEAD AND TO MAKE AN 'ALL CALL' ANNOUNCEMENT TO THE CABIN CREW. SHORTLY AFTER HE FINISHED TALKING WITH HER (WITHIN 2-3 MINS) WE FELT A SLIGHT 'NIBBLE' OF TURB THEN SUDDENLY A SEVERE JOLT. SINCE IT WAS MY LEG AND I WAS FLYING I GOT ON THE GAUGES IMMEDIATELY TO CHK OUR CONDITION. ATTITUDE WAS LEVEL BUT AIRSPD JUMPED 20 KTS AND ALT CLBED 200 FT. AFTER 2-3 SECONDS AIRSPD DROPPED 40 KTS (20 KTS BELOW BUG SPD) AND ALT DROPPED 400 FT. THE ENCOUNTER WAS OVER IN A MATTER OF SECONDS BUT WE CONTINUED IN LIGHT-MODERATE CHOP FOR AT LEAST 30 MINS. MY GUESS (SPECULATION) IS THAT WE PASSED THROUGH THE VORTEX CORE OF THE JET STREAM. THE JOLT WAS SEVERE ENOUGH THAT I FIGURED IF ANYONE WAS NOT STRAPPED IN IN THE REAR OF THE ACFT WE MIGHT HAVE SOME INJURIES. UNFORTUNATELY WE DID AND 6 PAX WHO DID NOT HAVE THEIR SEAT BELTS FASTENED RECEIVED MINOR INJURIES. THANK GOODNESS NONE WERE SERIOUS AND THEY WERE TREATED RELEASED AT A LCL BAY AREA HOSPITAL AFTER ARR AT SFO. ALTHOUGH FLYING WILL NEVER BE A RISK FREE ENVIRONMENT; I OFFER THE FOLLOWING SUGGESTIONS TO INCREASE SAFETY: TAKE PIREPS AND SIGMETS SERIOUSLY -- DON'T ASSUME YOU HAVE 200 MI TO PREPARE. ALWAYS HAVE RADAR ON AT NIGHT; EVEN IN VMC. ALTHOUGH IT MIGHT NOT PICK UP CAT; IT DOESN'T HURT TO HAVE IT ON. THE FAA SHOULD CONSIDER REQUIRING ALL PAX TO KEEP THEIR SEAT BELTS FASTENED WHILE SEATED -- EVEN WHEN THE SEAT BELT SIGN IS OFF. THIS PRACTICE WORKS ON THE NATION'S HIGHWAYS AND WOULD HELP PREVENT THESE SORTS OF UPSETS ON THE AIRWAYS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS RPTR THINKS THAT THIS WAS THE MOST VIOLENT TURB ENCOUNTER HE HAS EVER HAD. HE WAS MILDLY SURPRISED THAT THE ACFT WITHSTOOD IT SO WELL; IN FACT THE AUTOPLT STAYED ENGAGED. HIS ONLY FUTURE ACTION WOULD BE TO HAVE THE RADAR ON WITH THE TURB MODE DISPLAYING IN THE HOPE THAT THE SHEAR WOULD BE SHOWN ON THE SCOPE AND HE COULD AVOID IT. THE CREW WAS ON A B747- 400 AND THEY HAD SEVERAL WARNINGS THAT TURB HAD BEEN ENCOUNTERED AHEAD OF THEM. THE CAPT HAD JUST BRIEFED THE PURSER ON THE PIREPS WHEN THEY HIT THE TURB. ALTHOUGH THE SEAT BELT SIGNS WERE ON A NUMBER OF PAX DID NOT HAVE THEIR SEAT BELTS FASTENED AND SOME OF THE PAX AND THE FLT ATTENDANTS WERE STANDING. AFTER THE SEVERE TURB; WHICH LASTED ABOUT 40 SECONDS ACCORDING TO THE RPTR; THE ACFT STAYED IN MODERATE TURB FOR ABOUT 40 MINS. DURING THE LATTER PHASE OF TURB THE CAPT ATTEMPTED TO ESCAPE THE ROUGH RIDE BY TURNING TO THE N; BUT AFTER A WHILE HE GAVE UP AND RETURNED TO COURSE.