INFLT ENG SHUTDOWN REQUIRES A DIVERSION TO ALTERNATE. PRIMARY ELECTRICAL SUPPLY PROB PRECEDED THE ENG SHUTDOWN.

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FLT PLAN WAS (PWM) PORTLAND; ME; TO (IAD) WASHINGTON; DULLES. AFTER DEP; WHILE AT FL240; RIGHT GENERATOR FAILED ON A BA-4100. SHORTLY THEREAFTER VIBRATION AND NOISE WERE NOTED COMING FROM R ENG. CHKLIST WAS COMPLETED FOR THE GENERATOR FAILURE AND FLT WAS CONTINUED. APPROX 30 MIN AFTER GENERATOR FAILED; VIBRATIONS BECAME CONTINUOUS AND TORQUE BEGAN TO RISE AND FALL. THE ERRATIC ENG MEMORY ITEMS WERE ACCOMPLISHED AND ENG WAS SHUT DOWN. WE DECLARED THE EMER AND DIVERTED INTO PROVIDENCE LNDG WITHOUT FURTHER INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE NORMAL MEANS OF SHUTTING DOWN A FAILED GENERATOR IS TO COMPLY WITH THE CHKLIST AND ACTUATE THE ELECTRICAL CONTACTOR SWITCH WHICH TURNS THE GENERATOR OFF. THIS SHOULD ALLOW THE SHAFT TO AUTO SHEAR FROM THE ENG. THAT DID NOT HAPPEN. FO FEELS THAT THIS DESIGN IS MARGINAL AT BEST AND FELT THAT THE ONLY REASON THE CAPT HAD INITIALLY ELECTED TO CONTINUE THE FLT (UP TO THE POINT OF ENG VIBRATIONS) WAS THAT THE ENRTE WX WAS SO CLR. HE STATED THAT THIS ACFT HAS MARGINAL LEVELS OF ELECTRICAL GENERATION.