Narrative:

Steady cruise at FL350. 50 NM north of ZZZ; #1 engine generator fell off line and would not rest per procedure. CSD oil pressure/temperature ok. Generator just fell off bus. APU would not start. Descended to FL250; waited 5 mins and attempted to start the APU again. Would not start. Contacted dispatch and maintenance control. Maintenance control had me try one more start on APU with no success. With only 1 generator operating; dispatch and I agreed that it was time to declare an emergency and divert to ZZZ. Recovery and landing uneventful. Callback conversation with reporter revealed the following information: the reporter stated the #1 CSD temperature and oil pressure was normal and the generator just dropped off the bus with the 'generator fail warning' illuminated. Any attempt to reset the generator failed. The APU would not start at cruise altitude and after descending to FL250 still would not start. This airplane was overnight'ed at a station that dropped to 22 degrees below zero and was really cold soaked. 2 attempts on the ground and it started and operated normally. The contract technician checked the #1 CSD and found the oil black.

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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 #1 GENERATOR AND UNABLE TO START APU AT ANY ALT.

Narrative: STEADY CRUISE AT FL350. 50 NM N OF ZZZ; #1 ENG GENERATOR FELL OFF LINE AND WOULD NOT REST PER PROC. CSD OIL PRESSURE/TEMP OK. GENERATOR JUST FELL OFF BUS. APU WOULD NOT START. DSNDED TO FL250; WAITED 5 MINS AND ATTEMPTED TO START THE APU AGAIN. WOULD NOT START. CONTACTED DISPATCH AND MAINT CTL. MAINT CTL HAD ME TRY ONE MORE START ON APU WITH NO SUCCESS. WITH ONLY 1 GENERATOR OPERATING; DISPATCH AND I AGREED THAT IT WAS TIME TO DECLARE AN EMER AND DIVERT TO ZZZ. RECOVERY AND LNDG UNEVENTFUL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE #1 CSD TEMP AND OIL PRESSURE WAS NORMAL AND THE GENERATOR JUST DROPPED OFF THE BUS WITH THE 'GENERATOR FAIL WARNING' ILLUMINATED. ANY ATTEMPT TO RESET THE GENERATOR FAILED. THE APU WOULD NOT START AT CRUISE ALT AND AFTER DSNDING TO FL250 STILL WOULD NOT START. THIS AIRPLANE WAS OVERNIGHT'ED AT A STATION THAT DROPPED TO 22 DEGS BELOW ZERO AND WAS REALLY COLD SOAKED. 2 ATTEMPTS ON THE GND AND IT STARTED AND OPERATED NORMALLY. THE CONTRACT TECHNICIAN CHKED THE #1 CSD AND FOUND THE OIL BLACK.

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.