THE CREW OF AN MD80 EXPERIENCED LOSS OF CABIN PRESSURE AT 10000 FT DURING CLBOUT.

Narrative

ON INITIAL CLBOUT; EARS POPPED. ASKED THE FO IF THE CABIN WAS PRESSURIZING AND HE STATED EVERYTHING WAS NORMAL. AFTER PASSING 10000 FT; GOT A CABIN ALT LIGHT AND AURAL WARNING. IMMEDIATELY LEVELED OFF AT 11000 FT AND INFORMED ZLA OF OUR PROB. AFTER RUNNING THE 'UNSCHEDULED CABIN CLBING' CHKLIST WE GOT THE CABIN STABILIZED AND INFORMED ZLA THAT WE WANTED A STEP-CLB AT 13000 FT. LOST THE CABIN AGAIN AND DECLARED AN EMER WITH ZLA. RAN THE 'RAPID DEPRESSURIZATION' CHKLIST AND RETURNED TO LAX FOR AN UNEVENTFUL LNDG. SUPPLEMENTAL INFO FROM ACN 509899: ON CLBOUT FROM BUR; ACFT APPEARED TO PRESSURIZE NORMALLY. PASSING 10000 FT (CLRED TO 13000 FT) WE GOT CABIN ALT LIGHT AND AURAL WARNING. CAPT LEVELED ACFT AT 11000 FT. FO TOLD ATC WE HAD A PRESSURIZATION PROB AND NEEDED TO LEVEL OFF. WENT TO FLOW LIGHT OR UNSCHEDULED CLB CHKLIST. ALL WAS NORMAL AND PRESSURIZATION STABILIZED. CAPT CLBED TO 13000 FT. CABIN BEGAN TO CLB AGAIN AND LIGHT AND AURAL WARNING APPEARED. RAN RAPID DEPRESSURIZATION CHKLIST AND GOT CABIN TO PRESSURIZE NORMALLY IN MANUAL. SUDDENLY CABIN BEGAN ANOTHER UNSCHEDULED CLB; GOT LIGHT AND AURAL WARNING. CAPT DECLARED AN EMER AND DSNDED TO 10000 FT. OPERATED PRESSURIZATION IN MANUAL. UNEVENTFUL DIVERSION TO LAX.