Narrative:

On climb out form mexico city airport (ele 7340') we experienced a cabin altitude alert horn. We had been cleared directly to FL350 and were climbing our medium large transport aircraft at maximum rate. Before action could be taken to reverse the climb of the cabin the oxygen masks dropped in the passenger compartment. The passengers subsequently donned the masks. I as first officer was trying to isolate the problem as well as deal with the now incoming calls from the flight attendants and mex departure control. In attempting to solve the problem I cycled the bleeds and went manual on the out flow valve to make sure it was closed. The cabin began to pressurize and the trip was continued to san antonio, tx without further incident. The question is did I forget to turn the bleeds on prior to takeoff? The bleed switch position was not noted by myself or the captain as being off upon reading the receiving aircraft checklist. We had brought this same aircraft in the night before and the position that I left the bleed switches in was on with the APU on and providing cabin air conditioning. Even when maintenance shut down the APU the bleed should have been left on. In conclusion I would like to say that yes it is possible that we both overlooked the bleed switch position. A possible remedy to this occurring again would be to add this switch position to the recall button that you push as part of your taxi checklist. As it is now when you mess press recall you get no indication that your engine bleed switches are off. Supplemental information from acn #88317: enroute to sat became confronted with problem of severe WX. I made decision to top building WX at 33000'.

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Original NASA ASRS Text

Title: ACR MLG ALLOWED CABIN ALT TO CLIMB ABOVE 10000 MSL CAUSING PASSENGER MASKS TO DROP. PRESSURIZATION RECOVERED FLT THEN CONTINUED TO DESTINATION BUT FLEW ILLEGAL ABOVE 25000 MSL ACCOUNT AUTO PRESENTATION PAX OXYGEN NO LONGER AVAILABLE.

Narrative: ON CLIMB OUT FORM MEXICO CITY ARPT (ELE 7340') WE EXPERIENCED A CABIN ALT ALERT HORN. WE HAD BEEN CLRED DIRECTLY TO FL350 AND WERE CLIMBING OUR MLG ACFT AT MAX RATE. BEFORE ACTION COULD BE TAKEN TO REVERSE THE CLIMB OF THE CABIN THE OXYGEN MASKS DROPPED IN THE PASSENGER COMPARTMENT. THE PASSENGERS SUBSEQUENTLY DONNED THE MASKS. I AS F/O WAS TRYING TO ISOLATE THE PROBLEM AS WELL AS DEAL WITH THE NOW INCOMING CALLS FROM THE FLT ATTENDANTS AND MEX DEP CTL. IN ATTEMPTING TO SOLVE THE PROBLEM I CYCLED THE BLEEDS AND WENT MANUAL ON THE OUT FLOW VALVE TO MAKE SURE IT WAS CLOSED. THE CABIN BEGAN TO PRESSURIZE AND THE TRIP WAS CONTINUED TO SAN ANTONIO, TX WITHOUT FURTHER INCIDENT. THE QUESTION IS DID I FORGET TO TURN THE BLEEDS ON PRIOR TO TKOF? THE BLEED SWITCH POSITION WAS NOT NOTED BY MYSELF OR THE CAPT AS BEING OFF UPON READING THE RECEIVING ACFT CHECKLIST. WE HAD BROUGHT THIS SAME ACFT IN THE NIGHT BEFORE AND THE POSITION THAT I LEFT THE BLEED SWITCHES IN WAS ON WITH THE APU ON AND PROVIDING CABIN AIR CONDITIONING. EVEN WHEN MAINT SHUT DOWN THE APU THE BLEED SHOULD HAVE BEEN LEFT ON. IN CONCLUSION I WOULD LIKE TO SAY THAT YES IT IS POSSIBLE THAT WE BOTH OVERLOOKED THE BLEED SWITCH POSITION. A POSSIBLE REMEDY TO THIS OCCURRING AGAIN WOULD BE TO ADD THIS SWITCH POSITION TO THE RECALL BUTTON THAT YOU PUSH AS PART OF YOUR TAXI CHECKLIST. AS IT IS NOW WHEN YOU MESS PRESS RECALL YOU GET NO INDICATION THAT YOUR ENGINE BLEED SWITCHES ARE OFF. SUPPLEMENTAL INFORMATION FROM ACN #88317: ENROUTE TO SAT BECAME CONFRONTED WITH PROBLEM OF SEVERE WX. I MADE DECISION TO TOP BUILDING WX AT 33000'.

Data retrieved from NASA's ASRS site as of August 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.