Narrative:

Approximately 5 hours into the flight; the aircraft electrical system became unstable with lights and systems shutting off; then on repeatedly. We contacted 767 maintenance via satcom. The best we could determine is the right integrated drive generator (idg); although; not showing an EICAS warning had over temped; and was putting out bad volts and freq. I elected to turn off the generator verses disconnecting the idg; as that is a non-reversible action. The system stabilized. The APU had been placarded inoperative by maintenance. I acted under captain emergency authority to attempt to start the APU to gain second electrical source as [base] advised they showed the item cleared. Two attempts were made to start the APU to no avail. Now down to a single electrical source; we made plans to divert to an enroute airport; approximately 160 mn north of our position. Approach and landing was normal and aircraft was removed from service.an operative APU would have allowed us to continue to destination.

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Original NASA ASRS Text

Title: A B767-300 Captain disconnected the right Integrated Drive Generator (IDG) in flight because of electrical system anomalies which the crew suspected was caused by an overheating IDG. The flight diverted to an enroute airport.

Narrative: Approximately 5 hours into the flight; the aircraft electrical system became unstable with lights and systems shutting off; then on repeatedly. We contacted 767 Maintenance via SATCOM. The best we could determine is the right Integrated Drive Generator (IDG); although; not showing an EICAS warning had over temped; and was putting out bad volts and freq. I elected to turn off the generator verses disconnecting the IDG; as that is a non-reversible action. The system stabilized. The APU had been placarded INOP by maintenance. I acted under Captain emergency authority to attempt to start the APU to gain second electrical source as [base] advised they showed the item cleared. Two attempts were made to start the APU to no avail. Now down to a single electrical source; we made plans to divert to an enroute airport; approximately 160 mn north of our position. Approach and landing was normal and aircraft was removed from service.An operative APU would have allowed us to continue to destination.

Data retrieved from NASA's ASRS site 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.