AN MD80; ON CLB AT 10000 FT; DECLARED AN EMER DUE TO THE L CONSTANT SPD DRIVE OVERTEMP OFF SCALE. CREW DID NOT DISCONNECT CONSTANT SPD DRIVE AND RETURNED TO DEP ARPT WHERE A MAINT INSPECTION REVEALED THAT THE CONSTANT SPD DRIVE HAD COME APART.

Narrative

UPON ARR AT ZZZ FROM ZZZ1 WHILE ON THE RAMP; THE L GENERATOR TRIPPED OFF LINE AND WOULD NOT RESET. WE DEFERRED THE GENERATOR UNDER A PROVISION THAT ALLOWS FOR THE GENERATOR TO BE TURNED OFF BUT LEAVE THE CSD CONNECTED. AFTER TKOF FROM ZZZ; THE CSD STARTED A SLOW RISE IN TEMPERATURE UNTIL IT WENT COMPLETELY OFF SCALE. WHEN THE TEMP ROSE THROUGH ABOUT 140 DEGS; WE RAN THE CSD HIGH OIL TEMP CHKLIST AND ATTEMPTED TO DISCONNECT THE CSD. THE TEMP CONTINUED TO RISE EVEN AFTER WE ATTEMPTED THE DISCONNECT. WE MADE THE DECISION TO RETURN TO ZZZ CONCERNED THAT THE CSD OIL TEMP WAS OFF SCALE HIGH (ABOVE 180 DEGS). MADE AN UNEVENTFUL OVERWT LNDG IN ZZZ.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: INDICATIONS ON GENERATOR WERE 50 VOLTS WITH NO FREQUENCY INDICATIONS. THE RPTR CONTACTED MAINT CTL AND MADE DECISION TO DEFER; PER THE MEL; THE L GENERATOR AS INOPERATIVE AND THE CONTRACT TECHNICIAN CALLED TO ACCOMPLISH SPECIAL PROCS INCLUDING OIL QUANTITY CHK OF THE CONSTANT SPD DRIVE AND AUX POWER UNIT. ALL SPECIAL PROCS IN THE MEL WERE ACCOMPLISHED EXCEPT THE CONSTANT SPD DRIVE WAS NOT DISCONNECTED DUE TO THE COMPANY POLICY OF NOT DISCONNECTING THE CONSTANT SPD DRIVE IF THE CREW AND THE MAINT CTLR AGREE THE GENERATOR FAULT WAS NOT SPEED RELATED. THE RPTR STATED THE AIRPLANE WAS DISPATCHED. IN CLB AT 10000 FT; THE CONSTANT SPD DRIVE TEMP WENT OUT OF THE RED INDICATION SCALE. THE CONSTANT SPD DRIVE LOW OIL PRESSURE LIGHT ILLUMINATED AND REMAINED ON. THE RPTR NOTED THE CONSTANT SPD DISCONNECT SWITCH HAD TO BE HELD FOR AT LEAST 50 SECONDS BEFORE DISCONNECT WAS ACCOMPLISHED; NORMAL TIME IS 3 SECONDS. AN EMER WAS DECLARED AND THE FLT RETURNED TO DEP ARPT. THE CONTRACT TECHNICIAN ON ARR; APCHED THE ENG AND SMELLED HOT OIL. TECHNICIAN THEN OPENED THE OIL SOAKED COWLING AND DISCOVERED THE CONSTANT SPD DRIVE HAD COME APART AND THE OIL SIGHT GAUGE HAD BLOWN OUT. THE RPTR STATED THAT IN HINDSIGHT; THE CONSTANT SPD DRIVE SHOULD HAVE BEEN DISCONNECTED PRIOR TO DEP.