Narrative:

At top of descent; 75 NM from ZZZ1; '#2 generator hot' caution illuminated. Conducted EAC which directs crew to turn off respective generator. Approximately 10 seconds after shutting off generator #2; caution extinguished. Called maintenance controller from air. Upon arrival; a mechanic met the airplane and announced maintenance's intent of MEL'ing generator #2. I immediately was hesitant because: 1) MEL is for gcu; which seemed to be operating normally until we shut it off. 2) MEL directs maintenance to inspect visually for signs of overheat (implying that an overheat would be unacceptable). We didn't need to inspect. The caution system revealed an overheat. I relayed this information to maintenance control and wanted an interpretation from someone with operational control. I requested dispatch have the duty officer call me. The duty officer called. I relayed above concerns and requested an interpretation whether MEL relief would be legal. Duty officer enthusiastically said flight was absolutely legal because: 1) there were no visual signs of overheat (MEL wording) so structural integrity was intact. 2) if the generator control was selected off and no further overheat was detected; the gcu could be considered inoperative for the purpose of that MEL. I requested that duty officer consult maintenance control about system operation and call back. When duty officer called back duty officer had consulted maintenance control and said we were having conversation on recorded line (duty officer's solution to refusal to add remark on release). Duty officer said that flight would be safe and legal because maintenance said that the overheat sensor was passively connected to the gcu. Since the overheat caution extinguished when the gcu was selected off; it indicated a malfunction in the gcu which resulted in an incorrect overheat signal. With this information in hand (and no reason to doubt it); I elected to proceed to ZZZ2 after aircraft was MEL'ed by outstation mechanic. At top of descent into ZZZ2; the #2 dc generator caution light once again illuminated. We ran checklist; but no crew action was taken even though gcu was already off. Uneventful landing. Maintenance elected to change out generator #2. Now curious; I observed mechanic remove generator and asked him if he could tell whether the generator really was running hot. He attempted to turn generator armature with little success and said that he thought the bearing in it seemed to be failing and was causing excessive friction and heat. This is a problem because I now believe that the aircraft should have been either repaired in ZZZ1 or the generator removed from the accessory box and ferried. Unclr wording and intent of MEL; judicious interpretation of MEL legality by maintenance control and duty officer. Possibly incorrect facts about system operation relayed to flight crew influenced crew's acceptance of MEL for that flight. Change MEL to more clearly reflect conditions for its use. Compel duty officers to add amendments to releases to reflect ultimate result of discussions about operational suitability (at captain's discretion). Ensure operational pressures do not influence maintenance control and duty officer's interps. Make sure maintenance controllers and duty officers are familiar with respective system operation before issuing system guidance to flight crews.

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Original NASA ASRS Text

Title: A DH8-Q200 'GEN HOT' CAUTION LIGHT ILLUMINATED. MAINT MEL'ED THE GEN WITH THE GCU OFF. MEL WAS INCORRECT BECAUSE A DAMAGED BEARING WAS DISCOVERED AFTER A SECOND FLT WHEN THE 'GEN HOT' LIGHT AGAIN ILLUMINATED.

Narrative: AT TOP OF DSCNT; 75 NM FROM ZZZ1; '#2 GENERATOR HOT' CAUTION ILLUMINATED. CONDUCTED EAC WHICH DIRECTS CREW TO TURN OFF RESPECTIVE GENERATOR. APPROX 10 SECONDS AFTER SHUTTING OFF GENERATOR #2; CAUTION EXTINGUISHED. CALLED MAINT CTLR FROM AIR. UPON ARR; A MECH MET THE AIRPLANE AND ANNOUNCED MAINT'S INTENT OF MEL'ING GENERATOR #2. I IMMEDIATELY WAS HESITANT BECAUSE: 1) MEL IS FOR GCU; WHICH SEEMED TO BE OPERATING NORMALLY UNTIL WE SHUT IT OFF. 2) MEL DIRECTS MAINT TO INSPECT VISUALLY FOR SIGNS OF OVERHEAT (IMPLYING THAT AN OVERHEAT WOULD BE UNACCEPTABLE). WE DIDN'T NEED TO INSPECT. THE CAUTION SYS REVEALED AN OVERHEAT. I RELAYED THIS INFO TO MAINT CTL AND WANTED AN INTERP FROM SOMEONE WITH OPERATIONAL CTL. I REQUESTED DISPATCH HAVE THE DUTY OFFICER CALL ME. THE DUTY OFFICER CALLED. I RELAYED ABOVE CONCERNS AND REQUESTED AN INTERP WHETHER MEL RELIEF WOULD BE LEGAL. DUTY OFFICER ENTHUSIASTICALLY SAID FLT WAS ABSOLUTELY LEGAL BECAUSE: 1) THERE WERE NO VISUAL SIGNS OF OVERHEAT (MEL WORDING) SO STRUCTURAL INTEGRITY WAS INTACT. 2) IF THE GENERATOR CTL WAS SELECTED OFF AND NO FURTHER OVERHEAT WAS DETECTED; THE GCU COULD BE CONSIDERED INOP FOR THE PURPOSE OF THAT MEL. I REQUESTED THAT DUTY OFFICER CONSULT MAINT CTL ABOUT SYS OP AND CALL BACK. WHEN DUTY OFFICER CALLED BACK DUTY OFFICER HAD CONSULTED MAINT CTL AND SAID WE WERE HAVING CONVERSATION ON RECORDED LINE (DUTY OFFICER'S SOLUTION TO REFUSAL TO ADD REMARK ON RELEASE). DUTY OFFICER SAID THAT FLT WOULD BE SAFE AND LEGAL BECAUSE MAINT SAID THAT THE OVERHEAT SENSOR WAS PASSIVELY CONNECTED TO THE GCU. SINCE THE OVERHEAT CAUTION EXTINGUISHED WHEN THE GCU WAS SELECTED OFF; IT INDICATED A MALFUNCTION IN THE GCU WHICH RESULTED IN AN INCORRECT OVERHEAT SIGNAL. WITH THIS INFO IN HAND (AND NO REASON TO DOUBT IT); I ELECTED TO PROCEED TO ZZZ2 AFTER ACFT WAS MEL'ED BY OUTSTATION MECH. AT TOP OF DSCNT INTO ZZZ2; THE #2 DC GENERATOR CAUTION LIGHT ONCE AGAIN ILLUMINATED. WE RAN CHKLIST; BUT NO CREW ACTION WAS TAKEN EVEN THOUGH GCU WAS ALREADY OFF. UNEVENTFUL LNDG. MAINT ELECTED TO CHANGE OUT GENERATOR #2. NOW CURIOUS; I OBSERVED MECH REMOVE GENERATOR AND ASKED HIM IF HE COULD TELL WHETHER THE GENERATOR REALLY WAS RUNNING HOT. HE ATTEMPTED TO TURN GENERATOR ARMATURE WITH LITTLE SUCCESS AND SAID THAT HE THOUGHT THE BEARING IN IT SEEMED TO BE FAILING AND WAS CAUSING EXCESSIVE FRICTION AND HEAT. THIS IS A PROB BECAUSE I NOW BELIEVE THAT THE ACFT SHOULD HAVE BEEN EITHER REPAIRED IN ZZZ1 OR THE GENERATOR REMOVED FROM THE ACCESSORY BOX AND FERRIED. UNCLR WORDING AND INTENT OF MEL; JUDICIOUS INTERP OF MEL LEGALITY BY MAINT CTL AND DUTY OFFICER. POSSIBLY INCORRECT FACTS ABOUT SYS OP RELAYED TO FLT CREW INFLUENCED CREW'S ACCEPTANCE OF MEL FOR THAT FLT. CHANGE MEL TO MORE CLEARLY REFLECT CONDITIONS FOR ITS USE. COMPEL DUTY OFFICERS TO ADD AMENDMENTS TO RELEASES TO REFLECT ULTIMATE RESULT OF DISCUSSIONS ABOUT OPERATIONAL SUITABILITY (AT CAPT'S DISCRETION). ENSURE OPERATIONAL PRESSURES DO NOT INFLUENCE MAINT CTL AND DUTY OFFICER'S INTERPS. MAKE SURE MAINT CTLRS AND DUTY OFFICERS ARE FAMILIAR WITH RESPECTIVE SYS OP BEFORE ISSUING SYS GUIDANCE TO FLT CREWS.

Data retrieved from NASA's ASRS site as of May 2009 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.