Narrative:

Approximately 40nm from my destination on a 135 passenger carrying leg; the left alternator annunciator light illuminated. I ran the checklist; noted no change in the illuminated annunciator light and noted no load on the associated load meter. Per the checklist; I turned off the left alternator for the duration of the leg. I noted the loss of equipment to ATC; and continued on to land without event. After ending the 135 leg and dropping off my passengers; I was scheduled to fly an empty; part 91 ferry leg back to home base. Since this leg would be daytime; VFR; part 91; I assumed it would be legal to fly this leg with an inoperative alternator. But in an abundance of caution; I elected to call the home office to advise them of the situation and ensure my plan to fly the ferry leg with the inoperative alternator was in compliance with our operational specs. One of the company principals answered the phone and the chief pilot was present in the room with him during the conversation. I apprised them of the situation and was told that making the VFR ferry flight was fine. With this advice; I flew the airplane home with the left alternator turned off. The flight was uneventful. I did not at this time reference the MEL because I did not believe it applied to this part 91 leg; and because I did not think that the MEL would be more restrictive than the underlying part 91 daytime; VFR equipment requirement. Upon arriving at home base; I wrote up the alternator issue in the discrepancy log. The next day; maintenance informed me and the chief pilot that the alternator 'failure' was the result of a broken alternator drive shaft that had fallen back into the engine crank case and caused visible metal shards to be found in the engine sump. The chief pilot and I were both shocked at this news. At no time during any of the relevant flight legs was there any indication of any kind (aural; tactile; engine gauge; etc.) that there might be any engine issue. The affected engine ran normally and smoothly on all relevant legs. The chief pilot and I then referenced the issue in the aircraft MEL; something neither of us had done previously. The MEL stated that the plane could be flown in with an illuminated alternator annunciator during day VFR flight as long as the affected alternator had been inspected and found to be operable. The MEL also stated that it did not cover flight conducted under part 91.so technically; I was legal. But I still feel like I made a huge mistake by relying on the advice of others when I should have checked the MEL. My sense is that the MEL language referenced above was included because this drive shaft failure was a known potential issue; however; the MEL made no reference to the potential severity of observing what normally would be considered a very benign annunciator indication.

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Original NASA ASRS Text

Title: BE58 pilot experiences an alternator failure on a part 135 flight and lands safely at the destination airport. The reporter contacts the Chief Pilot to ensure that a part 91 ferry flight back to base with the alternator inoperative is legal and is told that it is. The flight is uneventful but maintenance informs that the Alternator 'failure' was the result of a broken alternator drive shaft that had fallen back into the engine crank case and caused damage.

Narrative: Approximately 40nm from my destination on a 135 passenger carrying leg; the left Alternator Annunciator light illuminated. I ran the checklist; noted no change in the illuminated annunciator light and noted no load on the associated load meter. Per the checklist; I turned off the left Alternator for the duration of the leg. I noted the loss of equipment to ATC; and continued on to land without event. After ending the 135 leg and dropping off my passengers; I was scheduled to fly an empty; Part 91 ferry leg back to home base. Since this leg would be daytime; VFR; Part 91; I assumed it would be legal to fly this leg with an inoperative alternator. But in an abundance of caution; I elected to call the home office to advise them of the situation and ensure my plan to fly the ferry leg with the inoperative alternator was in compliance with our Operational Specs. One of the company Principals answered the phone and the Chief Pilot was present in the room with him during the conversation. I apprised them of the situation and was told that making the VFR ferry flight was fine. With this advice; I flew the airplane home with the left alternator turned off. The flight was uneventful. I did not at this time reference the MEL because I did not believe it applied to this part 91 leg; and because I did not think that the MEL would be more restrictive than the underlying Part 91 daytime; VFR equipment requirement. Upon arriving at home base; I wrote up the Alternator issue in the discrepancy log. The next day; maintenance informed me and the Chief Pilot that the Alternator 'failure' was the result of a broken alternator drive shaft that had fallen back into the engine crank case and caused visible metal shards to be found in the engine sump. The Chief Pilot and I were both shocked at this news. At no time during any of the relevant flight legs was there any indication of any kind (aural; tactile; engine gauge; etc.) that there might be any engine issue. The affected engine ran normally and smoothly on all relevant legs. The Chief Pilot and I then referenced the issue in the aircraft MEL; something neither of us had done previously. The MEL stated that the plane could be flown in with an illuminated alternator annunciator during day VFR flight as long as the affected alternator had been inspected and found to be operable. The MEL also stated that it did not cover flight conducted under Part 91.So technically; I was legal. But I still feel like I made a huge mistake by relying on the advice of others when I should have checked the MEL. My sense is that the MEL language referenced above was included because this drive shaft failure was a known potential issue; however; the MEL made no reference to the potential severity of observing what normally would be considered a very benign annunciator indication.

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.