Narrative:

My student and I were flying a routine cross-country flight. After crossing over ZZZ airport; both my student and I noticed a faint 'winding' sound and started to smell a burning smell that was electrical in nature. We did not notice any smoke inside the cabin. Originally thinking it was an electrical issue within the cabin; we reverted back to past training on troubleshooting electrical issues within the cabin. During our troubleshooting process; we climbed 300 feet high of our assigned altitude of 6;000' feet MSL (mean sea level) accidentally. At first we shut down the electronics via the master switch; then turned all switches off; then master on; and subsequently the other electrical switches but couldn't find any evidence of smoke or fire in the cabin; however we still smelled the same level of the burning smell that was electrical in nature throughout our troubleshooting process. After troubleshooting the interior electrical system; I noticed the 'M' bus amps indication as yellow flashing and '-6.0'. We did not check to see if there was a 'low volts' indication on the pfd (primary flight display) since we automatically assumed the issue to be related to the alternator and the sense of panic was starting to take over. We did however find the 'low volts annunciator' checklist; and started that checklist since we assumed the issue to be related to the alternator. At that time; ATC (air traffic control) started to consume my mental processes and asked if we wanted to divert; and if we wanted to declare an emergency. Since I was unsure of the burning smell and was leery of an engine fire; I decided to declare and emergency and was reminded ZZZ airport was behind us; I forgot to squawk 7700. While that was happening we totally switched gears to landing mode because ZZZ was so close; and we did not complete the 'low volts annunciator' checklist to its entirety. We diverted to ZZZZ and during final approach to land on runway xx at ZZZ; ATC asked if we wanted emergency vehicles there to meet us. Again; because I was leery of an engine fire; I asked that emergency services be there. After a normal landing without incident; we found a parking spot; shut down the aircraft and waited for emergency services. I called the local FSS (flight service station) to close our flight plan; and called one of the flight school owners to notify our situation. When the fire services came; they checked for any signs of fire and found no signs of fire. Even with all electrical power shut off and the engine shut down; we still could smell the burning smell that was electrical in nature from the front right of the engine cowling. After some time; the owner of the flight school called with one of our contracted mechanics (a&P/ia) (airframe & powerplant/inspection authorized) and we walked through some checks. We found that when the master switched 'on'; the 'alt field' circuit breaker popped; and with a second check; it popped again. The general consensus was the alternator was the suspected; but not confirmed; issue. Before we left the aircraft at ZZZ; we tied down the aircraft; secured the control lock; closed all windows and doors; and took walk-around photos of the aircraft parked. We found no damage to any surfaces on the aircraft and no visible signs of any fire. The day after; a mechanic was flown out to the aircraft parked at ZZZ. The mechanic found the 'power' lead of the alternator to be disconnected and in turn grounded itself to the alternator which cause the alternator to 'burn' out; this the confirmed case of alternator failure.

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Original NASA ASRS Text

Title: Flight instructor and student flying a C172 aircraft encountered alternator failure inflight.

Narrative: My student and I were flying a routine cross-country flight. After crossing over ZZZ airport; both my student and I noticed a faint 'winding' sound and started to smell a burning smell that was electrical in nature. We did not notice any smoke inside the cabin. Originally thinking it was an electrical issue within the cabin; we reverted back to past training on troubleshooting electrical issues within the cabin. During our troubleshooting process; we climbed 300 feet high of our assigned altitude of 6;000' feet MSL (Mean Sea Level) accidentally. At first we shut down the electronics via the master switch; then turned all switches off; then master on; and subsequently the other electrical switches but couldn't find any evidence of smoke or fire in the cabin; however we still smelled the same level of the burning smell that was electrical in nature throughout our troubleshooting process. After troubleshooting the interior electrical system; I noticed the 'M' bus amps indication as yellow flashing and '-6.0'. We did not check to see if there was a 'Low Volts' indication on the PFD (Primary Flight Display) since we automatically assumed the issue to be related to the alternator and the sense of panic was starting to take over. We did however find the 'Low Volts Annunciator' checklist; and started that checklist since we assumed the issue to be related to the alternator. At that time; ATC (Air Traffic Control) started to consume my mental processes and asked if we wanted to divert; and if we wanted to declare an emergency. Since I was unsure of the burning smell and was leery of an engine fire; I decided to declare and emergency and was reminded ZZZ airport was behind us; I forgot to squawk 7700. While that was happening we totally switched gears to landing mode because ZZZ was so close; and we did not complete the 'Low Volts Annunciator' checklist to its entirety. We diverted to ZZZZ and during final approach to land on Runway XX at ZZZ; ATC asked if we wanted emergency vehicles there to meet us. Again; because I was leery of an engine fire; I asked that emergency services be there. After a normal landing without incident; we found a parking spot; shut down the aircraft and waited for emergency services. I called the Local FSS (Flight Service Station) to close our flight plan; and called one of the flight school owners to notify our situation. When the fire services came; they checked for any signs of fire and found no signs of fire. Even with all electrical power shut off and the engine shut down; we still could smell the burning smell that was electrical in nature from the front right of the engine cowling. After some time; the owner of the flight school called with one of our contracted mechanics (A&P/IA) (Airframe & Powerplant/Inspection Authorized) and we walked through some checks. We found that when the master switched 'on'; the 'Alt Field' circuit breaker popped; and with a second check; it popped again. The general consensus was the alternator was the suspected; but not confirmed; issue. Before we left the aircraft at ZZZ; we tied down the aircraft; secured the control lock; closed all windows and doors; and took walk-around photos of the aircraft parked. We found no damage to any surfaces on the aircraft and no visible signs of any fire. The day after; a mechanic was flown out to the aircraft parked at ZZZ. The mechanic found the 'power' lead of the alternator to be disconnected and in turn grounded itself to the alternator which cause the alternator to 'burn' out; this the confirmed case of alternator failure.

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.