TURB ENCOUNTER NEAR SPARTANBURG; SC.

Narrative

IN CRUISE AT FL330; .78 MACH. ACFT WAS IMC AND EXPERIENCING LIGHT CHOP. WX RADAR WAS OPERATING AND PAINTING NO RETURNS ALONG OUR RTE OF FLT. WITHOUT WARNING; ACFT ENTERED INTENSE CONVECTIVE PHENOMENON. ACFT EXPERIENCED SEVERE TURB AS IT FIRST LOST ALT; FOLLOWED BY AN ALT GAIN; FOLLOWED BY ANOTHER LOSS. ACFT DEVIATED BTWN 32500 FT AND 33500 FT MSL. ACFT WAS BEING FLOWN BY AUTOPLT WHEN INCIDENT BEGAN; BUT LOST BOTH THE PITCH AND ROLL MODES DURING ALT EXCURSIONS. INCIDENT LASTED 20-30 SECONDS. PLTS ASSUMED CTL FROM AUTOPLT AND RETURNED TO STABLE CONDITIONS AT FL330 AS TURB ENDED. WHEN THE INCIDENT OCCURRED; THE SEAT BELT SIGN WAS ON AND THE FLT ATTENDANTS WERE CONDUCTING THEIR SVC. THE FLT ATTENDANTS RPTED NO INJURIES TO THEMSELVES AND AT THE TIME RPTED NO INJURIES TO PAX. DURING THE DEPLANING AT DCA; 1 PAX STATED SHE HAD A SORE NECK. NONE OF THE PLTS HAD EXPERIENCED ANYTHING LIKE THAT BEFORE. WE ADVISED ATC OR OUR ALTDEV BUT WE WERE NOT EXPLICIT. WE DID NOT SAY WE HAD EXPERIENCED 30 SECONDS OF SEVERE TURB AS WE SHOULD HAVE STATED. WE SHOULD ALSO HAVE EXPLICIT INFORMED ATC WE WERE UNABLE TO MAINTAIN ASSIGNED ALT; RATHER THAN SAYING WE HAD DEVIATED FROM OUR ASSIGNED ALT DUE TO WX. THE INCIDENT ITSELF WAS UNAVOIDABLE. IN HINDSIGHT; I WOULD HAVE BEEN MUCH MORE EXPLICIT AND INFORMATIVE IN COMMUNICATING OUR EXPERIENCE TO ATC. I SHOULD HAVE GIVEN A PIREP RATHER THAN MERELY ADVISING OF OUR ALTDEV.