Narrative:

Both pilots were reserve captains with limited experience in aircraft and seat. XA55 home base sign in with diversion for WX at destination. Event occurred in cruise with approx. 12 hours of duty time after a divert and on our 4th leg of the day; captain flying. Approximately 1 hour into our flight in cruise at FL290 mach .77 our first indication of a problem was the uncommanded disconnect of the autopilot and autothrottles. As we regained control of the aircraft it appeared that the left engine was rolling back. We checked the annunciator panel and had numerous annunciators including mach trim; yaw dampener; stall indicator; left gen; left CSD and I believe others that I can not recall. The captain's flight instruments were also erratic and intermittent with flickering displays and a rolling heading indicator. We declared an emergency and advised ATC that it appeared we had lost the left engine. ATC recommended an airport and we elected to divert there and began our descent. Along with the mentioned problems we became aware of an intermittent clicking sound and flickering lights and displays that I normally associate with the main buses changing power sources. It happened frequently throughout the descent. During the descent the electrical power began to stabilize and we realized that the engine was producing normal thrust throughout the event and that it may be only an electrical problem. We checked the CSD gauges and noticed the left CSD temp pegged at red line. We started the APU and began the CSD low oil pressure checklist as that was one of our numerous annuciators. The first officer (first officer) ran the CSD low oil pressure checklist and disconnected the left CSD as directed by the checklist and we brought the APU on the left bus per the checklist. At this time we were in holding at 7;000 feet; as we elected to burn fuel so as to not land over max landing weight. Still over our max landing weight and with the situation stabilized and our problem now clear; and with two operating gen's we elected to rescind the emergency and change our divert to [an airport] better suited to handle the passengers and aircraft. I transferred control of the aircraft to the first officer so I could better communicate with ATC; company; flight attendant's and passengers. We landed with no further incident.it was very confusing with the faulty engine and flight instrument indications as a result of (I'm guessing) an unstable left bus due to the unusual nature of the CSD failure. I believe that the left CSD failed in an unusual manner causing the left gen and crosstie to switch back and forth repeatedly as the left CSD went on and off speed. It is not at all how we had been trained for a CSD; bus or gen fault. The unusual failure combined with fatigue and my inexperience as a captain and on the S80 led me to make a hasty decision. If I had a 'do over'; I would like to have delayed my decision and taken more time to evaluate the situation. It wouldn't have taken long to realize that the airspeed was not bleeding off despite the erratic engine indications and that the real problem was solely electrical which would then have lead me to the proper course which would have probably been to start the APU; disconnect the left CSD per the checklist and continue to our original destination.

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Original NASA ASRS Text

Title: During cruise flight the crew of an MD-83 experienced autopilot and autothrottle disconnects as well as numerous annunciator warnings along with erratic flight instrument failures. The nature of the fault indications initially led the Captain to believe that an engine failure had occurred. An emergency was declared and a diversion initiated. The true nature of the problem was eventually determined to be a CSD failure; appropriate procedures were followed; and the flight continued uneventfully to the original destination airport.

Narrative: Both pilots were reserve captains with limited experience in aircraft and seat. XA55 home base sign in with diversion for WX at destination. Event occurred in cruise with approx. 12 hours of duty time after a divert and on our 4th leg of the day; Captain flying. Approximately 1 hour into our flight in cruise at FL290 Mach .77 our first indication of a problem was the uncommanded disconnect of the autopilot and autothrottles. As we regained control of the aircraft it appeared that the left engine was rolling back. We checked the annunciator panel and had numerous annunciators including Mach Trim; Yaw Dampener; Stall Indicator; L Gen; L CSD and I believe others that I can not recall. The Captain's flight instruments were also erratic and intermittent with flickering displays and a rolling heading indicator. We declared an emergency and advised ATC that it appeared we had lost the left engine. ATC recommended an airport and we elected to divert there and began our descent. Along with the mentioned problems we became aware of an intermittent clicking sound and flickering lights and displays that I normally associate with the Main Buses changing power sources. It happened frequently throughout the descent. During the descent the electrical power began to stabilize and we realized that the engine was producing normal thrust throughout the event and that it may be only an electrical problem. We checked the CSD gauges and noticed the L CSD Temp pegged at red line. We started the APU and began the CSD Low Oil Pressure Checklist as that was one of our numerous annuciators. The First Officer (FO) ran the CSD Low Oil Pressure Checklist and disconnected the left CSD as directed by the checklist and we brought the APU on the left bus per the checklist. At this time we were in holding at 7;000 feet; as we elected to burn fuel so as to not land over Max Landing weight. Still over our max landing weight and with the situation stabilized and our problem now clear; and with two operating GEN's we elected to rescind the emergency and change our divert to [an airport] better suited to handle the passengers and aircraft. I transferred control of the aircraft to the FO so I could better communicate with ATC; Company; flight attendant's and passengers. We landed with no further incident.It was very confusing with the faulty engine and flight instrument indications as a result of (I'm guessing) an unstable L Bus due to the unusual nature of the CSD failure. I believe that the L CSD failed in an unusual manner causing the L GEN and Crosstie to switch back and forth repeatedly as the L CSD went on and off speed. It is not at all how we had been trained for a CSD; BUS or GEN fault. The unusual failure combined with fatigue and my inexperience as a Captain and on the S80 led me to make a hasty decision. If I had a 'do over'; I would like to have delayed my decision and taken more time to evaluate the situation. It wouldn't have taken long to realize that the airspeed was not bleeding off despite the erratic engine indications and that the real problem was solely electrical which would then have lead me to the proper course which would have probably been to start the APU; disconnect the L CSD per the checklist and continue to our original destination.

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.