Narrative:

In the vicinity of VOR at FL350 we were just starting to deviate around some isolated thunderstorms when we experienced an electrical disruption. We isolated the problem to be a popped xfer bus #1 circuit breaker. We lost several items on board such as automatic pressurization; WX radar; captain's instruments; egpws; #1 aft fuel pump; yaw damper; ACARS; and both FMC's. There were no lights illuminated on the electrical panel. I started the APU and powered the #1 bus. This was of no help. The pressurization system was having difficulty holding the cabin (climbed to 9500 ft). The first officer was able to fly the aircraft with raw data. Soon after; the autoplt and autothrottle disconnected. I consulted the flight manual for an irregular procedure that addressed our situation. There was not a specific checklist that we could reference. I elected to push in the circuit breaker in accordance with the circuit breaker resetting policy. We were able to restore the entire system. I set up a phone patch with dispatch and maintenance control. We discussed the circuit breakers in question. The maintenance controller also addressed some circuit breakers that we would need to keep an eye on. Approximately 5 mins later the circuit breaker popped again. We were able to reestablish the phone patch. The maintenance controller recommended we push the breaker in again. We discussed the use of manual dc for pressurization and it functioned normally for the duration of the flight. Since we were day VMC and had restored everything; we elected to continue. Approximately 10 mins later; the circuit breaker popped again. I elected to leave the breaker out. We declared an emergency and now focused all of our attention on the approach and landing in ZZZ which was now our nearest suitable airport. ATC offered an approach to runway xx but the ILS was OTS. We elected to use runway yy. I switched the EFIS to both on right to recapture my instruments; but was not successful. The first officer executed a visual approach backed up by raw data. The emergency equipment was standing by. On final approach we had an anti-skid inoperative light illuminate. The approach; landing and rollout were normal with the exception of a #1 reverser light unlock light not illuminated; the reverser operated normally. I was able to taxi to the gate normally. During the descent I briefed the chief purser as to the nature of the problem; but elected to not brief the passenger as all indications in the cabin were normal. I did make an announcement at the gate that we experienced a 'loss of a system' and thus the reason for the emergency equipment. I completed a thorough review of all irregular procedures and still could not find an appropriate procedure. I discussed the situation with the gate mechanic who 'guessed' that it may have been a relay problem. Callback conversation with reporter revealed the following information: the reporter stated the cause of the loss of the #1 xfer bus is unknown as maintenance has not released any information. A second hand report has the #1 transformer rectifier being the culprit but reporter discounted that report.

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Original NASA ASRS Text

Title: A B737-300 IN CRUISE AT FL350 DECLARED AN EMER AND DIVERTED DUE TO LOSS OF THE XFER BUS #1 AND RELATED EFIS; AUTOPLT; #1 AFT FUEL PUMP AND OTHER SYS POWERED FROM THE #1 XFER BUS.

Narrative: IN THE VICINITY OF VOR AT FL350 WE WERE JUST STARTING TO DEVIATE AROUND SOME ISOLATED TSTMS WHEN WE EXPERIENCED AN ELECTRICAL DISRUPTION. WE ISOLATED THE PROB TO BE A POPPED XFER BUS #1 CIRCUIT BREAKER. WE LOST SEVERAL ITEMS ON BOARD SUCH AS AUTO PRESSURIZATION; WX RADAR; CAPT'S INSTS; EGPWS; #1 AFT FUEL PUMP; YAW DAMPER; ACARS; AND BOTH FMC'S. THERE WERE NO LIGHTS ILLUMINATED ON THE ELECTRICAL PANEL. I STARTED THE APU AND POWERED THE #1 BUS. THIS WAS OF NO HELP. THE PRESSURIZATION SYS WAS HAVING DIFFICULTY HOLDING THE CABIN (CLBED TO 9500 FT). THE FO WAS ABLE TO FLY THE ACFT WITH RAW DATA. SOON AFTER; THE AUTOPLT AND AUTOTHROTTLE DISCONNECTED. I CONSULTED THE FLT MANUAL FOR AN IRREGULAR PROC THAT ADDRESSED OUR SITUATION. THERE WAS NOT A SPECIFIC CHKLIST THAT WE COULD REF. I ELECTED TO PUSH IN THE CIRCUIT BREAKER IN ACCORDANCE WITH THE CIRCUIT BREAKER RESETTING POLICY. WE WERE ABLE TO RESTORE THE ENTIRE SYS. I SET UP A PHONE PATCH WITH DISPATCH AND MAINT CTL. WE DISCUSSED THE CIRCUIT BREAKERS IN QUESTION. THE MAINT CTLR ALSO ADDRESSED SOME CIRCUIT BREAKERS THAT WE WOULD NEED TO KEEP AN EYE ON. APPROX 5 MINS LATER THE CIRCUIT BREAKER POPPED AGAIN. WE WERE ABLE TO REESTABLISH THE PHONE PATCH. THE MAINT CTLR RECOMMENDED WE PUSH THE BREAKER IN AGAIN. WE DISCUSSED THE USE OF MANUAL DC FOR PRESSURIZATION AND IT FUNCTIONED NORMALLY FOR THE DURATION OF THE FLT. SINCE WE WERE DAY VMC AND HAD RESTORED EVERYTHING; WE ELECTED TO CONTINUE. APPROX 10 MINS LATER; THE CIRCUIT BREAKER POPPED AGAIN. I ELECTED TO LEAVE THE BREAKER OUT. WE DECLARED AN EMER AND NOW FOCUSED ALL OF OUR ATTN ON THE APCH AND LNDG IN ZZZ WHICH WAS NOW OUR NEAREST SUITABLE ARPT. ATC OFFERED AN APCH TO RWY XX BUT THE ILS WAS OTS. WE ELECTED TO USE RWY YY. I SWITCHED THE EFIS TO BOTH ON R TO RECAPTURE MY INSTS; BUT WAS NOT SUCCESSFUL. THE FO EXECUTED A VISUAL APCH BACKED UP BY RAW DATA. THE EMER EQUIP WAS STANDING BY. ON FINAL APCH WE HAD AN ANTI-SKID INOP LIGHT ILLUMINATE. THE APCH; LNDG AND ROLLOUT WERE NORMAL WITH THE EXCEPTION OF A #1 REVERSER LIGHT UNLOCK LIGHT NOT ILLUMINATED; THE REVERSER OPERATED NORMALLY. I WAS ABLE TO TAXI TO THE GATE NORMALLY. DURING THE DSCNT I BRIEFED THE CHIEF PURSER AS TO THE NATURE OF THE PROB; BUT ELECTED TO NOT BRIEF THE PAX AS ALL INDICATIONS IN THE CABIN WERE NORMAL. I DID MAKE AN ANNOUNCEMENT AT THE GATE THAT WE EXPERIENCED A 'LOSS OF A SYS' AND THUS THE REASON FOR THE EMER EQUIP. I COMPLETED A THOROUGH REVIEW OF ALL IRREGULAR PROCS AND STILL COULD NOT FIND AN APPROPRIATE PROC. I DISCUSSED THE SITUATION WITH THE GATE MECH WHO 'GUESSED' THAT IT MAY HAVE BEEN A RELAY PROB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CAUSE OF THE LOSS OF THE #1 XFER BUS IS UNKNOWN AS MAINT HAS NOT RELEASED ANY INFO. A SECOND HAND RPT HAS THE #1 TRANSFORMER RECTIFIER BEING THE CULPRIT BUT RPTR DISCOUNTED THAT RPT.

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.