LGT ACFT IN CRUISE ENCOUNTERED SEVERE TURB. ACFT AIRSPD INCREASED INTO OVERSPD WARNING AND VIOLENT TURB AS RPTR CAPT TOOK OVER ACFT; REDUCING PWR; REDUCING AIRSPD BY USE OF SPOILERS.

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THE FLT WAS A SCHEDULED ACR PAX FLT FROM SLC TO STL IN A B727-200. THE FLT WAS OPERATING AT FL330 IN LEVEL CRUISE. PRIOR TO ENCOUNTERING THE SEVERE TURB; THE FLT HAD EXPERIENCED ONLY SMALL AREAS OF INTERMITTENT LIGHT CHOP. THE FLT HAD MOSTLY BEEN ABOVE THE CLOUD LAYERS; OPERATING IN CLR AIR OR INTERMITTENT HIGH CLOUDS. THE FLT WAS FLYING AN ATC ASSIGNED HDG FOR NAV TO THE ANX VOR. THE FO WAS THE PF. THE SEAT BELT SIGN HAD BEEN ON AND OFF DURING THE FLT. ABOUT 10-15 MINS PRIOR TO THE TURB; THE FO HAD UPDATED THE PAX AS TO OUR ETA; LOCATION; TURNED THE SEAT BELT SIGN OFF AND MADE HIS ANNOUNCEMENT TO KEEP THE BELTS FASTENED WHILE IN THEIR SEATS. ZDV ISSUED US A RPT THAT THERE WERE AREAS OF LIGHT; MODERATE; AND SEVERE TURB IN THE AREA FROM FL290 TO FL370. THE CLOUD LAYERS BELOW US CLRED. WITHOUT ANY WARNING THE ACFT ENTERED THE TURB. THE ACFT HAD AN ABRUPT AIRSPD INCREASE (MACH OVERSPD WARNING) FOLLOWED BY VIOLENT TURB. I TOOK COMMAND OF THE FLT CTLS. REDUCED PWR. PUT ON IGNITION; AND USED SPOILER TO REDUCE SPD. ALT INCREASED BY ABOUT 300 FT. FO REQUESTED AND RECEIVED CLRNC TO DSND TO FL290 SOON AFTER INITIAL ENCOUNTER. THE FE PUT SEAT BELT SIGN ON AT THE START OF THE TURB WHILE THE FO WAS OBTAINING THE CLRNC TO DSND TO FL290. DURING THE DSCNT TO FL290 THE FE OPENED THE DOOR TO SEE HOW THE CABIN AND PAX WERE DOING. WE DSNDED TO FL290. TOTAL DURATION OF SEVERE TURB WAS 2-3 MINS. THE ACFT REMAINED CTLABLE THROUGHOUT THE TURB. THE LOCATION AT THE TIME OF THE TURB WAS W OF DENVER JUST E OF THE MOUNTAINS. I MADE A PA ANNOUNCEMENT AFTER LEVELING AT FL290 FOR A FLT ATTENDANT TO RPT TO THE COCKPIT. THE FLT ATTENDANTS CAME FORWARD AND SAID THAT THERE WERE NO APPARENT INJURIES. THE SVC HAD BEEN COMPLETED AND CARTS HAD BEEN STOWED PRIOR TO THE ENCOUNTER. I ASKED THE FLT ATTENDANTS TO CHK EACH OF THE PAX AND RPT BACK. AFTER CHKING BACK WITH ME THEY SAID THAT IT APPEARED EVERYONE HAD BEEN IN THEIR SEATS AT THE ONSET. I ASKED ALL THE FLT ATTENDANTS TO CHK AND QUESTION EACH PAX TO ASCERTAIN IF THERE HAD BEEN INJURIES. I TOLD THE FLT ATTENDANTS THAT WE WERE CLOSE TO DEN AND COULD LAND VERY QUICKLY. AFTER A THOROUGH CHKING AND QUESTIONING BY ALL 4 FLT ATTENDANTS; I WAS TOLD THERE WERE NO INJURIES. SPILLED BEVERAGES APPEARED TO BE THE ONLY THING THAT HAPPENED. THE FO MADE A WALK THROUGH THE CABIN TALKING TO THE PEOPLE ABOUT 10 MINS AFTER THE TURB. NO ONE THAT HE SPOKE TO INDICATED THAT THEY WERE HURT. THE REMAINDER OF THE FLT WAS UNEVENTFUL. THE PAX APPEARED FINE AS THEY DISEMBARKED. THE FO AND MYSELF STOOD AT THE DOORWAY DURING THE DISEMBARKATION. WE DID NOT HEAR ANY COMPLAINTS OF INJURY FROM THE PAX.