AN LF31A FLC NEAR PMD AT APPROX FL490 EXPERIENCED AN AUTO PRESSURIZATION CONTROLLER FAILURE AND BEGAN A DSCNT. DURING THE DSCNT AT FL480 THE FLC LOST CTL OF THE CABIN PRESSURE AND INITIATED AN EMER DSCNT.

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THE PURPOSE OF THIS FLT WAS TO REPOSITION FROM SJC TO TUS. THERE WERE NO PAX. WE WERE IN A BLOCK ALT FL470-FL510 APPROX 30 NM ESE OF PMD. LEVEL AT FL488 THE CABIN LIGHT ILLUMINATED. CABIN ALT WAS READING 8000 FT. A NORMAL DSCNT WAS INITIATED. THE CABIN AT THIS TIME WAS BEING MANUALLY CTLED TO DSND AT 700 FPM (AUTO MODE INOP WITH CABIN LIGHT). ABOUT FL480; CTL OF CABIN PRESSURE WAS LOST SUDDENLY; THE RATE OF CLB NEEDLE WAS PEGGED (MAX INDICATION IS 6000 FPM). MANUAL CTL WAS NOT EFFECTIVE. WARNING HORN WITHIN SECONDS. EMER DSCNT PROCS INITIATED. ON THE WAY DOWN; MY RADIO XMISSIONS WERE DIFFICULT FOR ATC TO UNDERSTAND DUE TO THE OXYGEN MASK. I HAD 1 TA IN THE 30'S HOWEVER; ZLA GAVE US A HDG THAT CANCELED IT IN SECONDS. THEY GAVE US A CLR PATH TO PALM SPRINGS. APCHING PSP AT FL180 WE REGAINED A SAFE CABIN ALT. I DECIDED WE COULD SAFELY MAKE THE SHORT FLT TO TUS. ADDITIONALLY; THIS WOULD GIVE US TIME TO CLR UP THE CHKLISTS AND PROPERLY BRIEF FOR AN UNHURRIED LNDG. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT MAINT HAS REPLACED THE PRESSURIZATION CTL MODULE AND THAT DURING THE TIME OF THIS EVENT THE FLC WERE ABLE TO VERIFY THAT THEIR PROB WAS THE CONTROLLER BECAUSE THEY COULD HEAR THAT THE OUTFLOW VALVE WAS TRYING TO REGULATE THE PRESSURE.