B757 CREW ENCOUNTERS TURB W OF ALS.

Narrative

BEST RPTED ALT ACCORDING TO ATC AND PIREPS RPTED FROM DISPATCH WAS FL330 WITH LIGHT CHOP. WE WERE AT FL330 AND ABOUT 20 MINS W OF ALS WHEN ATC TOLD US THAT THERE HAD BEEN PIREPS ISOLATED IN THE VICINITY OF ALS OF LIGHT CHOP TO OCCASIONAL MODERATE TURB WITH SOME MOUNTAIN WAVE -- AGAIN FL330 BEST RPTED RIDE WITH QUITE A BIT OF TFC ON THE RTE AND NOT ALL FLTS WERE ENCOUNTERING IT. I IMMEDIATELY TURNED ON THE SEATBELT SIGN AND WE ADJUSTED OUR AIRSPD TO MACH .78; WHICH WAS BEST TURB SPD; AS A PRECAUTION. APCHING ALS; THERE WAS NO CHANGE IN OUR RIDE OF OCCASIONAL LIGHT CHOP. THERE WERE NO CLOUDS AND AUTOTHROTTLES AND AUTOPLT WERE ON AND WORKING NORMALLY. I HAD LOOKED AWAY FROM THE INST PANEL FOR NO MORE THAN 20 SECONDS AND IN THAT TIME THE AIRSPD HAD GONE FROM MACH .78 TO MACH .86; WHICH WAS BARBER POLE. THE AUTOTHROTTLES WERE RESPONDING BY RETARDING THE THROTTLES BUT NOT FAST ENOUGH TO KEEP THE OVERSPD FROM GOING OFF; SO WE PULLED THEM MANUALLY ALL THE WAY TO IDLE. EVEN THEN IT WAS ABOUT ANOTHER 10 SECONDS BEFORE THE AIRSPD STARTED TO DECREASE. THE AUTOPLT WAS DOING A GOOD JOB OF MAINTAINING OUR ALT. AS THE AIRSPD WAS SLOWING THROUGH MACH .84; I WAS CONCERNED ABOUT IT DROPPING OFF AS DRASTICALLY AS IT HAD INCREASED WHEN WE WOULD CROSS THE OTHER SIDE OF THE MOUNTAIN WAVE; SO I TOLD THE FO (WHO WAS FLYING) TO PUSH UP THE THROTTLES JUST OUT OF IDLE SO THAT THE ENGS WOULD BE ABLE TO RESPOND MORE QUICKLY IF WE SUDDENLY NEEDED THE PWR. JUST AT ABOUT THAT TIME WE ENCOUNTERED SEVERE TURB CHARACTERIZED BY RAPID; VIOLENT JOLTS; WITH SOME ROLLING MOTION. THERE WAS NOT MUCH IN THE WAY OF UP- AND DOWNDRAFTS ASSOCIATED WITH THE TURB; WHICH I BELIEVE IS WHY NONE OF THE FLT ATTENDANTS WERE INJURED. THEY WERE THE ONLY ONES NOT SEATED AT THE TIME. ALL OF THE PAX WERE STRAPPED IN -- MOST HAD BEEN ASLEEP. AS SOON AS WE HIT THE TURB; WE IMMEDIATELY NOTIFIED ATC AND GOT A DSCNT TO FL290 TO TRY TO ESCAPE IT AND AFTER ABOUT 20 SECONDS WE WERE OUT OF IT -- BACK IN JUST OCCASIONAL LIGHT CHOP. A CHK OF THE FLT ATTENDANTS AND CABIN REVEALED NO INJURIES; AND ALL THE ACFT SYS AND OPS APPEARED NORMAL. I CALLED DISPATCH RIGHT AWAY WITH OUR PIREP AND MADE A WRITE-UP IN THE ACFT LOG REGARDING THE SEVERE TURB ENCOUNTER.