Narrative:

While cruising at 17000 ft on air carrier airlines flight xyz from evansville, in, to detroit, mi, we experienced a generator overtemp annunciator on the left generator and performed the emergency checklist. As instructed, we shut down the left generator by opening the relay. The left generator light illuminated, confirming this. The left generator overtemp light extinguished after approximately 2 mins. Overheat condition resolved. Maintenance was notified. The flight was in VMC and agreed with company to continue to dtw. After about 10 mins, the left overtemp light reilluminated. Dispatch was notified along with maintenance the flight was now diverting to indianapolis. In our judgement it was the safest decision because there was no more procedure to follow and we wanted a mechanic to look at the generator. We notified ZAU and declared an emergency as our left engine began to vibrate with variations in torque. Once the power was reduced for descent, we decided to keep the engine running as all other indications (oil propeller and engine, torque, itt, ng) were relatively stable and engine was producing power. Callback conversation with reporter revealed the following information: the reporter stated the problem was a mechanically failed generator but was not advised if the generator actually came apart. The reporter said the generator cooling overboard vent was all sooted up and was a good indication that the generator was internally disintegrating.

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Original NASA ASRS Text

Title: A SAAB 340 IN CRUISE AT 17000 FT DECLARED AN EMER AND DIVERTED DUE TO THE L DC GENERATOR FAILURE AND L ENG VIBRATIONS.

Narrative: WHILE CRUISING AT 17000 FT ON ACR AIRLINES FLT XYZ FROM EVANSVILLE, IN, TO DETROIT, MI, WE EXPERIENCED A GENERATOR OVERTEMP ANNUNCIATOR ON THE L GENERATOR AND PERFORMED THE EMER CHKLIST. AS INSTRUCTED, WE SHUT DOWN THE L GENERATOR BY OPENING THE RELAY. THE L GENERATOR LIGHT ILLUMINATED, CONFIRMING THIS. THE L GENERATOR OVERTEMP LIGHT EXTINGUISHED AFTER APPROX 2 MINS. OVERHEAT CONDITION RESOLVED. MAINT WAS NOTIFIED. THE FLT WAS IN VMC AND AGREED WITH COMPANY TO CONTINUE TO DTW. AFTER ABOUT 10 MINS, THE L OVERTEMP LIGHT REILLUMINATED. DISPATCH WAS NOTIFIED ALONG WITH MAINT THE FLT WAS NOW DIVERTING TO INDIANAPOLIS. IN OUR JUDGEMENT IT WAS THE SAFEST DECISION BECAUSE THERE WAS NO MORE PROC TO FOLLOW AND WE WANTED A MECH TO LOOK AT THE GENERATOR. WE NOTIFIED ZAU AND DECLARED AN EMER AS OUR L ENG BEGAN TO VIBRATE WITH VARIATIONS IN TORQUE. ONCE THE PWR WAS REDUCED FOR DSCNT, WE DECIDED TO KEEP THE ENG RUNNING AS ALL OTHER INDICATIONS (OIL PROP AND ENG, TORQUE, ITT, NG) WERE RELATIVELY STABLE AND ENG WAS PRODUCING PWR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE PROB WAS A MECHANICALLY FAILED GENERATOR BUT WAS NOT ADVISED IF THE GENERATOR ACTUALLY CAME APART. THE RPTR SAID THE GENERATOR COOLING OVERBOARD VENT WAS ALL SOOTED UP AND WAS A GOOD INDICATION THAT THE GENERATOR WAS INTERNALLY DISINTEGRATING.

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.