Narrative:

Shortly after reaching FL210, we lost the #2 dc generator along with a dc bus #2, inverter #2, bus tie contactor, and dc service/utility bus. Since this is basically an 'electric' airplane, along with the above stated failures, we eventually lost both air data computers and the EFIS on the first officer's side. An emergency was then declared and we returned to sju. After completing all the checklists, an uneventful landing from a visual approach to runway 8 was executed, without any further complications. I believe the problem started with the failure of the #2 dc generator and quickly deteriorated with the bus tie contactor failure thereby faulting all the other #2 system. If the bus tie contactor would have worked correctly, all the #2 system could have automatically 'tied up' to the #1 generator (dc) and received their power from it. However, the failure of the #2 dc generator is considered a serious problem on the ATR42 series aircraft. The checklist 'dc generator fault' actually requires you to 'land at the nearest suitable airport' and avoid IMC conditions. A thorough amount of teamwork was required to return the aircraft back to sju. As a crew, I believe we did an excellent job, so did ATC in guiding us back to sju.

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Original NASA ASRS Text

Title: AN ATR42 CAPT RPTED A TOTAL ELECTRICAL FAILURE IN THE VICINITY OF COY, CAUSING HIM TO RETURN TO SJU, PR.

Narrative: SHORTLY AFTER REACHING FL210, WE LOST THE #2 DC GENERATOR ALONG WITH A DC BUS #2, INVERTER #2, BUS TIE CONTACTOR, AND DC SVC/UTILITY BUS. SINCE THIS IS BASICALLY AN 'ELECTRIC' AIRPLANE, ALONG WITH THE ABOVE STATED FAILURES, WE EVENTUALLY LOST BOTH AIR DATA COMPUTERS AND THE EFIS ON THE FO'S SIDE. AN EMER WAS THEN DECLARED AND WE RETURNED TO SJU. AFTER COMPLETING ALL THE CHKLISTS, AN UNEVENTFUL LNDG FROM A VISUAL APCH TO RWY 8 WAS EXECUTED, WITHOUT ANY FURTHER COMPLICATIONS. I BELIEVE THE PROB STARTED WITH THE FAILURE OF THE #2 DC GENERATOR AND QUICKLY DETERIORATED WITH THE BUS TIE CONTACTOR FAILURE THEREBY FAULTING ALL THE OTHER #2 SYS. IF THE BUS TIE CONTACTOR WOULD HAVE WORKED CORRECTLY, ALL THE #2 SYS COULD HAVE AUTOMATICALLY 'TIED UP' TO THE #1 GENERATOR (DC) AND RECEIVED THEIR PWR FROM IT. HOWEVER, THE FAILURE OF THE #2 DC GENERATOR IS CONSIDERED A SERIOUS PROB ON THE ATR42 SERIES ACFT. THE CHKLIST 'DC GENERATOR FAULT' ACTUALLY REQUIRES YOU TO 'LAND AT THE NEAREST SUITABLE ARPT' AND AVOID IMC CONDITIONS. A THOROUGH AMOUNT OF TEAMWORK WAS REQUIRED TO RETURN THE ACFT BACK TO SJU. AS A CREW, I BELIEVE WE DID AN EXCELLENT JOB, SO DID ATC IN GUIDING US BACK TO SJU.

Data retrieved from NASA's ASRS site as of July 2007 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.