RETURN LAND IN DC10-15 AFTER LOSS OF CABIN PRESSURE ON CLBOUT. FUEL DUMPING PROB AROSE DURING CHKLIST USE.

Narrative

CLBING OUT OF LAS THE CABIN PRESSURE BEGAN TO DECREASE (INCREASING CABIN ALT). THE AIR-CONDITIONING PRESSURIZATION DUCT HAD SEPARATED CAUSING AIR PRESSURE TO BE VENTED OUTSIDE THE ACFT. AT APPROX 17000 FT MSL THE ACFT WAS LEVELED OFF AND A DSCNT INITIATED. CABIN ALT CLBED TO A MAX OF APPROX 9000 FT. A RETURN TO LAS WAS INITIATED AND FUEL DUMPING STARTED. THE AUTOMATIC FUEL DUMPING SHUTOFF WAS OBSERVED AFTER ONLY 10000 LBS OF FUEL HAD BEEN DUMPED; WELL BEFORE REACHING A LANDABLE GROSS WT. THE FUEL DUMPING PROC WAS SHUT DOWN AND REINITIATED RESULTING IN 10000 ADDITIONAL LBS OF FUEL DUMPING BEFORE THE AUTOMATIC SHUTOFF AGAIN STOPPED THE FUEL DUMPING. THE FUEL DUMP PROC WAS INITIATED 2 ADDITIONAL TIMES TO REACH A GROSS WT APPROPRIATE FOR LNDG. INITIAL INDICATIONS REVEAL A FAULTY TRANSFER PUMP RELAY MAY BE SENDING INFO ERRONEOUSLY TO THE AUTOMATIC SHUTOFF FEATURE WHICH SHUTS DOWN THE FUEL DUMP. THE LNDG WAS COMPLETED AT LAS UNEVENTFULLY. SUPPLEMENTAL INFO FROM ACN 341348: THERE WAS VERY LITTLE AIRFLOW IN CABIN; CAUSING 1 PAX TO COMPLAIN ABOUT HEART PROB. PAX WAS PUT ON OXYGEN. PARAMEDICS MET ACFT.