Narrative:

We were 200 miles east of ZZZ at FL360. We experienced a transponder failure with the #1 transponder. ATC notified us and we switched to the #2. The #2 apparently did not work either so we were checking circuit breakers when we hear the cabin warning horn go off. We looked up at the pressurization and noticed it was at 11000 ft and climbing. We donned our oxygen masks and proceeded with our memory items. I was the PNF and notified ATC that we lost our cabin and need to come down now. They immediately gave us FL240 then 16000 ft. The captain proceeded with the emergency descent and I continued with the checklist. I had gone from automatic on the controller to stby and then over to manual dc and made sure the outflow valve was closed. I proceeded to continue with the checklist when we received another group of caution lights. We got a low idle light and a GPWS inoperative light. We continued the descent down to 14000 ft in which we were cleared to by ATC. We noticed that the cabin did pressurize again in manual and had to open the outflow valve a little to control the cabin altitude. The checklist was complete and we continued to ZZZ. Upon landing in ZZZ; the stick shaker came on for about 1 minute then we received a master caution for the pressure. I looked up and both packs had tripped. We also received a buffer alert on the FMC. I reached up and turned the packs to the off position. Once they were off the pack trip lights eventually went off. The only thing I did not do correctly was declare an emergency and squawk 7700. ATC apparently did declare an emergency for us and understood the situation. Other than that; everything went like in the sim. This was a scenario that took a little thinking because of the different master cautions that were appearing during the descent.callback conversation with reporter revealed the following information: reporter stated that he has not heard from maintenance about the cause of this event; but when describing the indications to a check airman was told this appeared to be the classic ground air sense switch failure. The crew took about 2 mins to identify the warning horn as the cabin altitude warning because they were troubleshooting other abnormal indications that didnT seem to have a common cause. Because depressurization was occurring slowly; the cabin climbed slightly above 12000 ft. The crew did not hesitate to commence a descent once they identified the cabin altitude.

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Original NASA ASRS Text

Title: A B737-300 AT FL360 EXPERIENCED MULTIPLE SYSTEM ANOMALIES AND LOSS OF CABIN PRESSURIZATION. THERE WAS A DELAY IN RECOGNITION OF THE CABIN ALT WARNING HORN. AN EMER WAS DECLARED WITH AN EMER DSCNT.

Narrative: WE WERE 200 MILES EAST OF ZZZ AT FL360. WE EXPERIENCED A XPONDER FAILURE WITH THE #1 XPONDER. ATC NOTIFIED US AND WE SWITCHED TO THE #2. THE #2 APPARENTLY DID NOT WORK EITHER SO WE WERE CHKING CIRCUIT BREAKERS WHEN WE HEAR THE CABIN WARNING HORN GO OFF. WE LOOKED UP AT THE PRESSURIZATION AND NOTICED IT WAS AT 11000 FT AND CLBING. WE DONNED OUR OXYGEN MASKS AND PROCEEDED WITH OUR MEMORY ITEMS. I WAS THE PNF AND NOTIFIED ATC THAT WE LOST OUR CABIN AND NEED TO COME DOWN NOW. THEY IMMEDIATELY GAVE US FL240 THEN 16000 FT. THE CAPT PROCEEDED WITH THE EMER DSCNT AND I CONTINUED WITH THE CHKLIST. I HAD GONE FROM AUTO ON THE CTLR TO STBY AND THEN OVER TO MANUAL DC AND MADE SURE THE OUTFLOW VALVE WAS CLOSED. I PROCEEDED TO CONTINUE WITH THE CHKLIST WHEN WE RECEIVED ANOTHER GROUP OF CAUTION LIGHTS. WE GOT A LOW IDLE LIGHT AND A GPWS INOP LIGHT. WE CONTINUED THE DSCNT DOWN TO 14000 FT IN WHICH WE WERE CLRED TO BY ATC. WE NOTICED THAT THE CABIN DID PRESSURIZE AGAIN IN MANUAL AND HAD TO OPEN THE OUTFLOW VALVE A LITTLE TO CTL THE CABIN ALT. THE CHKLIST WAS COMPLETE AND WE CONTINUED TO ZZZ. UPON LNDG IN ZZZ; THE STICK SHAKER CAME ON FOR ABOUT 1 MINUTE THEN WE RECEIVED A MASTER CAUTION FOR THE PRESSURE. I LOOKED UP AND BOTH PACKS HAD TRIPPED. WE ALSO RECEIVED A BUFFER ALERT ON THE FMC. I REACHED UP AND TURNED THE PACKS TO THE OFF POSITION. ONCE THEY WERE OFF THE PACK TRIP LIGHTS EVENTUALLY WENT OFF. THE ONLY THING I DID NOT DO CORRECTLY WAS DECLARE AN EMER AND SQUAWK 7700. ATC APPARENTLY DID DECLARE AN EMER FOR US AND UNDERSTOOD THE SITUATION. OTHER THAN THAT; EVERYTHING WENT LIKE IN THE SIM. THIS WAS A SCENARIO THAT TOOK A LITTLE THINKING BECAUSE OF THE DIFFERENT MASTER CAUTIONS THAT WERE APPEARING DURING THE DSCNT.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE HAS NOT HEARD FROM MAINT ABOUT THE CAUSE OF THIS EVENT; BUT WHEN DESCRIBING THE INDICATIONS TO A CHK AIRMAN WAS TOLD THIS APPEARED TO BE THE CLASSIC GND AIR SENSE SWITCH FAILURE. THE CREW TOOK ABOUT 2 MINS TO IDENTIFY THE WARNING HORN AS THE CABIN ALT WARNING BECAUSE THEY WERE TROUBLESHOOTING OTHER ABNORMAL INDICATIONS THAT DIDNT SEEM TO HAVE A COMMON CAUSE. BECAUSE DEPRESSURIZATION WAS OCCURRING SLOWLY; THE CABIN CLBED SLIGHTLY ABOVE 12000 FT. THE CREW DID NOT HESITATE TO COMMENCE A DSCNT ONCE THEY IDENTIFIED THE CABIN ALT.

Data retrieved from NASA's ASRS site as of January 2009 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.