Narrative:

The purpose of this flight was to reposition from sjc to tus. There were no passenger. We were in a block altitude FL470-FL510 approximately 30 NM ese of pmd. Level at FL488 the cabin light illuminated. Cabin altitude was reading 8000 ft. A normal descent was initiated. The cabin at this time was being manually controled to descend at 700 FPM (automatic mode inoperative with cabin light). About FL480, control of cabin pressure was lost suddenly, the rate of climb needle was pegged (maximum indication is 6000 FPM). Manual control was not effective. Warning horn within seconds. Emergency descent procedures 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 heading that canceled it in seconds. They gave us a clear path to palm springs. Approaching psp at FL180 we regained a safe cabin altitude. I decided we could safely make the short flight to tus. Additionally, this would give us time to clear up the checklists and properly brief for an unhurried landing. Callback conversation with reporter revealed the following information: reporter states that maintenance has replaced the pressurization control module and that during the time of this event the flight crew were able to verify that their problem was the controller because they could hear that the outflow valve was trying to regulate the pressure.

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Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.