Narrative:

On apr/sat/96 air carrier flight xx mex-sfo we had a rapid cabin depressurization. At the time we were at FL350 1 hour from mexico city. We were VMC on direct routing to altar intersection. We asked mexico city control for the MEA in our area. He was unable to tell us. We descended to the sector altitude in VMC. At that altitude we were unable to talk to mmex except by relay through another air carrier flight in our vicinity. Callback conversation with reporter revealed the following information: reporter idented aircraft as A320. Cause of depressurization was a bad controller caused from faulty circuitry. Also, the A320 had 2 press controllers, the active one and a backup. During this incident, as per aircraft design, when the main controller failed and the outflow valve went to full open, the backup controller was designed to activate after 45 seconds, but with the outflow valve full open, 45 seconds was far too long of a delay. Since this incident plus two others experienced with this air carrier, airbus changed the circuitry so that now if a press controller fails there is only a 4 second delay before the backup takes over. The reporter was unhappy with the mexican controller working his flight. The controller was of no help in providing needed information to the flight crew, information such as the minimum vectoring altitude in their sector, etc.

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Original NASA ASRS Text

Title: ACFT EQUIP PROB. EMER DSCNT DUE TO DEPRESSURIZATION. FAULTY CIRCUITRY IN PRESSURE CTLR PLUS TOO LONG OF DELAY FOR BACKUP CTLR TO ACTIVATE. OXYGEN MASKS DEPLOYED AND CABIN ALT WENT TO 22000 FT.

Narrative: ON APR/SAT/96 ACR FLT XX MEX-SFO WE HAD A RAPID CABIN DEPRESSURIZATION. AT THE TIME WE WERE AT FL350 1 HR FROM MEXICO CITY. WE WERE VMC ON DIRECT ROUTING TO ALTAR INTXN. WE ASKED MEXICO CITY CTL FOR THE MEA IN OUR AREA. HE WAS UNABLE TO TELL US. WE DSNDED TO THE SECTOR ALT IN VMC. AT THAT ALT WE WERE UNABLE TO TALK TO MMEX EXCEPT BY RELAY THROUGH ANOTHER ACR FLT IN OUR VICINITY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR IDENTED ACFT AS A320. CAUSE OF DEPRESSURIZATION WAS A BAD CTLR CAUSED FROM FAULTY CIRCUITRY. ALSO, THE A320 HAD 2 PRESS CTLRS, THE ACTIVE ONE AND A BACKUP. DURING THIS INCIDENT, AS PER ACFT DESIGN, WHEN THE MAIN CTLR FAILED AND THE OUTFLOW VALVE WENT TO FULL OPEN, THE BACKUP CTLR WAS DESIGNED TO ACTIVATE AFTER 45 SECONDS, BUT WITH THE OUTFLOW VALVE FULL OPEN, 45 SECONDS WAS FAR TOO LONG OF A DELAY. SINCE THIS INCIDENT PLUS TWO OTHERS EXPERIENCED WITH THIS ACR, AIRBUS CHANGED THE CIRCUITRY SO THAT NOW IF A PRESS CTLR FAILS THERE IS ONLY A 4 SECOND DELAY BEFORE THE BACKUP TAKES OVER. THE RPTR WAS UNHAPPY WITH THE MEXICAN CTLR WORKING HIS FLT. THE CTLR WAS OF NO HELP IN PROVIDING NEEDED INFO TO THE FLC, INFO SUCH AS THE MINIMUM VECTORING ALT IN THEIR SECTOR, ETC.

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.