Narrative:

On climb out ATC said transponder failed, switched to no 2 and no help. Approximately 3 min later ATC informed xpond back on and then shortly after failed again. At this time the autothrottle tripped off. It later reset only to trip again. Passing 31000 we decided to start a descent to get a lower altitude until we sorted out the now 3 failures which seemed totally unrelated out. ATC gave us FL240. Approximately 3 min later the ground proximity fail light came on. That was enough for us and we asked for direct ZZZ I called the cabin and told the flight attendant #1 to put everything up and that we were returning to ZZZ. Approximately 2 min later what we thought was the takeoff warning horn came on. I told the first officer to just fly the aircraft and I contacted dispatch on the direct frequency and asked for maintenance. At this time we decide to forget ZZZ and divert to ZZZ1 which was right under us. While talking with maintenance master caution came on and the cabin oxygen light came on. At this time we realized we had lost control of the cabin and we declared an emergency and ran the two checklists. Notified the cabin when we were below 10000 and told them we were diverting to ZZZ1 and to expect to be on the ground in less than 10 min. In addition at this time the engine low idle light and the equipment cooling exhaust off light came on. Callback conversation with reporter revealed the following information: the reporter stated with the first failures of the ATC transponders the aircraft ground shift was suspected, but if this were the case a whole lot of systems would be failed at the same time. The reporter said as the aircraft climbed other systems began to fail progressively and when control of the cabin pressure was lost an emergency was declared and diversion initiated. The reporter stated maintenance found and replaced an intermittent squat sensor on the landing gear. Callback from acn 591080: the reporter stated because of the progressive failure of several systems the captain was suspecting a major malfunction or a possible electrical fire and we descended. The reporter said when the cabin pressure was lost it was time to declare an emergency and divert. The reporter stated the problem was reported to have been in the ground sensing circuit.

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Original NASA ASRS Text

Title: A B737-300 AT FL310 DECLARED AN EMER AND DIVERTED DUE TO SEVERAL VITAL ACFT SYSTEMS FAILING PROGRESSIVELY FOLLOWING A GROUND-AIR SWITCH FAILURE.

Narrative: ON CLB OUT ATC SAID XPONDER FAILED, SWITCHED TO NO 2 AND NO HELP. APPROX 3 MIN LATER ATC INFORMED XPOND BACK ON AND THEN SHORTLY AFTER FAILED AGAIN. AT THIS TIME THE AUTOTHROTTLE TRIPPED OFF. IT LATER RESET ONLY TO TRIP AGAIN. PASSING 31000 WE DECIDED TO START A DSCNT TO GET A LOWER ALT UNTIL WE SORTED OUT THE NOW 3 FAILURES WHICH SEEMED TOTALLY UNRELATED OUT. ATC GAVE US FL240. APPROX 3 MIN LATER THE GND PROX FAIL LIGHT CAME ON. THAT WAS ENOUGH FOR US AND WE ASKED FOR DIRECT ZZZ I CALLED THE CABIN AND TOLD THE FA #1 TO PUT EVERYTHING UP AND THAT WE WERE RETURNING TO ZZZ. APPROX 2 MIN LATER WHAT WE THOUGHT WAS THE TKOF WARNING HORN CAME ON. I TOLD THE FO TO JUST FLY THE ACFT AND I CONTACTED DISPATCH ON THE DIRECT FREQ AND ASKED FOR MAINT. AT THIS TIME WE DECIDE TO FORGET ZZZ AND DIVERT TO ZZZ1 WHICH WAS RIGHT UNDER US. WHILE TALKING WITH MAINT MASTER CAUTION CAME ON AND THE CABIN OXYGEN LIGHT CAME ON. AT THIS TIME WE REALIZED WE HAD LOST CTL OF THE CABIN AND WE DECLARED AN EMER AND RAN THE TWO CHKLISTS. NOTIFIED THE CABIN WHEN WE WERE BELOW 10000 AND TOLD THEM WE WERE DIVERTING TO ZZZ1 AND TO EXPECT TO BE ON THE GND IN LESS THAN 10 MIN. IN ADDITION AT THIS TIME THE ENG LOW IDLE LIGHT AND THE EQUIP COOLING EXHAUST OFF LIGHT CAME ON. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED WITH THE FIRST FAILURES OF THE ATC TRANSPONDERS THE ACFT GND SHIFT WAS SUSPECTED, BUT IF THIS WERE THE CASE A WHOLE LOT OF SYSTEMS WOULD BE FAILED AT THE SAME TIME. THE RPTR SAID AS THE ACFT CLBED OTHER SYSTEMS BEGAN TO FAIL PROGRESSIVELY AND WHEN CTL OF THE CABIN PRESSURE WAS LOST AN EMER WAS DECLARED AND DIVERSION INITIATED. THE RPTR STATED MAINT FOUND AND REPLACED AN INTERMITTENT SQUAT SENSOR ON THE LNDG GEAR. CALLBACK FROM ACN 591080: THE RPTR STATED BECAUSE OF THE PROGRESSIVE FAILURE OF SEVERAL SYSTEMS THE CAPTAIN WAS SUSPECTING A MAJOR MALFUNCTION OR A POSSIBLE ELECTRICAL FIRE AND WE DESCENDED. THE RPTR SAID WHEN THE CABIN PRESSURE WAS LOST IT WAS TIME TO DECLARE AN EMER AND DIVERT. THE RPTR STATED THE PROB WAS RPTED TO HAVE BEEN IN THE GND SENSING CIRCUIT.

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.