Narrative:

On previous flight; ATC was intermittently receiving our transponder. We followed checklists but still did not continuously work. Our autothrottle also would not stay engaged. On descent; we got a low idle light; do not use speed brake and the cabin pressure seemed not to be working properly. We wrote it up and the mechanic worked on it for a couple of hours. He could not find a problem so the company and mechanic signed it off as could not duplicate. On departure; ATC advised us again that they were not receiving our transponder. Our autothrottle also was not working. We attempted to get hold of company in the departure airport and finally reached dispatch through ACARS on level off FL310. Dispatch re-released us. We took a turn and then proceeded to get a cabin warning horn. We were losing pressurization. We started a descent; notified ATC and put on our oxygen masks. The captain was able to stop and control the cabin in manual mode. The captain pulled out the qrc and ran the depressurization checklist and emergency descent checklist. We continued down to 13;000. We notified the flight attendants of our incident and made sure that the masks did not drop in the back and that no one was injured in the descent. They confirmed that everyone was fine and that the masks did not drop. The cabin didn't get any higher than approximately 10;500 ft. We were already dispatched to a nearby airport; so we continued on with no further incidents. The mechanic and maintenance control were unable to diagnose the problem prior to departure.

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Original NASA ASRS Text

Title: A B737-400 pressurization control malfunctioned causing the Cabin Altitude Alert to sound so an emergency was declared and the flight diverted. The autothrottles and transponders were also malfunctioning.

Narrative: On previous flight; ATC was intermittently receiving our transponder. We followed checklists but still did not continuously work. Our autothrottle also would not stay engaged. On descent; we got a low idle light; do not use speed brake and the cabin pressure seemed not to be working properly. We wrote it up and the mechanic worked on it for a couple of hours. He could not find a problem so the Company and Mechanic signed it off as could not duplicate. On departure; ATC advised us again that they were not receiving our transponder. Our autothrottle also was not working. We attempted to get hold of company in the departure airport and finally reached Dispatch through ACARS on level off FL310. Dispatch re-released us. We took a turn and then proceeded to get a cabin warning horn. We were losing pressurization. We started a descent; notified ATC and put on our oxygen masks. The Captain was able to stop and control the cabin in manual mode. The Captain pulled out the QRC and ran the depressurization checklist and emergency descent checklist. We continued down to 13;000. We notified the flight attendants of our incident and made sure that the masks did not drop in the back and that no one was injured in the descent. They confirmed that everyone was fine and that the masks did not drop. The cabin didn't get any higher than approximately 10;500 FT. We were already dispatched to a nearby airport; so we continued on with no further incidents. The mechanic and Maintenance Control were unable to diagnose the problem prior to departure.

Data retrieved from NASA's ASRS site as of July 2013 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.