B737 PRESSURIZATION CONTROLLER FAILED; INCREASING PRESSURE IN CABIN.

Narrative

PASSING FL280 FOR FL290; CABIN BEGAN INTENSE DSCNT; DRIVING THE CABIN ALT DOWN FROM APPROX 4000 TO 0; AND DIFFERENTIAL PRESSURE TOWARD THE YELLOW ARC. ASSOCIATED EAR AND SINUS DISCOMFORT TO CREW AND PAX WAS STRONG. THE CABIN THEN REVERSED COURSE TOWARDS A CLB; THEN BACK TO AN INTENSE 4000 FPM PLUS DSCNT. I BRIEFED TO BEGIN THE MEMORY ITEMS FOR ABNORMAL PRESSURIZATION CHKLIST. I ATTEMPTED TO ALLEVIATE SOME OF THE PRESSURE BY TURNING OFF THE L PACK; WITH LITTLE OR NO CHANGE. SUBSEQUENTLY; THE FO ALSO THOUGHT TO TURN OFF THE R PACK; AND WE WERE MOMENTARILY DEPRESSURIZED; BUT I TURNED THE PACK BACK ON IMMEDIATELY. THE CABIN CONTINUED WILD GYRATIONS FROM AN APPROPRIATE CABIN ALT TO RAPID DSCNT; MAX DIFFERENTIAL; AND BACK TO RAPID CLB. THE CABIN ALT HORN THEN WENT OFF WITH A CABIN ALT APCHING 11000 FT. AT NO TIME WERE THERE ANY ASSOCIATED SYS FAULTS OR MASTER CAUTIONS. AFTER ESTABLISHING CREW COMS; I CONTINUED THE ABNORMAL PRESSURIZATION CHKLIST AND OPERATED THE PRESSURIZATION IN MANUAL MODE; WHICH DID STOP THE CABIN FROM CLBING FURTHER OR A FAST DSCNT. WE ASKED ATC FOR LOWER AND AN IMMEDIATE RETURN TO BWI. SUBSEQUENT APCH AND LNDG WERE UNEVENTFUL. ADD PROCS/TRAINING FOR DIFFERENTIAL EXCEEDANCE.