Narrative:

Items that run off our left main dc bus started to intermittently fail. Then all dc items on captain side died. After switching control to first officer we began troubleshooting. Pressurization was lost, temperature control was lost. At full hot cargo and cabin door warning lights illuminated. An emergency was declared and a landing at mfd, oh, was made. Landing was normal. Everything pointed to a left dc bus failure, however, none of the appropriate caution lights were on. In talking to maintenance afterward, they said the left generator surged and popped numerous circuit breakers. The gcu which controls bus ties and turns on caution lights became inoperative. Because of this, our situation was not displayed on the annunciator panel. Numerous caution lights illuminated, but they had nothing to do with this electrical system, which confused our initial conclusion.

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Original NASA ASRS Text

Title: LTT HAS ELECTRICAL DC BUS FAILURE. EMER DECLARED.

Narrative: ITEMS THAT RUN OFF OUR L MAIN DC BUS STARTED TO INTERMITTENTLY FAIL. THEN ALL DC ITEMS ON CAPT SIDE DIED. AFTER SWITCHING CTL TO FO WE BEGAN TROUBLESHOOTING. PRESSURIZATION WAS LOST, TEMP CTL WAS LOST. AT FULL HOT CARGO AND CABIN DOOR WARNING LIGHTS ILLUMINATED. AN EMER WAS DECLARED AND A LNDG AT MFD, OH, WAS MADE. LNDG WAS NORMAL. EVERYTHING POINTED TO A L DC BUS FAILURE, HOWEVER, NONE OF THE APPROPRIATE CAUTION LIGHTS WERE ON. IN TALKING TO MAINT AFTERWARD, THEY SAID THE L GENERATOR SURGED AND POPPED NUMEROUS CIRCUIT BREAKERS. THE GCU WHICH CTLS BUS TIES AND TURNS ON CAUTION LIGHTS BECAME INOP. BECAUSE OF THIS, OUR SIT WAS NOT DISPLAYED ON THE ANNUNCIATOR PANEL. NUMEROUS CAUTION LIGHTS ILLUMINATED, BUT THEY HAD NOTHING TO DO WITH THIS ELECTRICAL SYS, WHICH CONFUSED OUR INITIAL CONCLUSION.

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.