Narrative:

ATC reported the transponder code had been lost. Autoplt failed immediately following. Lights dimmed. Turned off all electrical except one communication set. Checked alternator circuit breaker ok, alternator switch cycled, no change. Landed at reedsville airport. The alternator warning light never activated. The a&P checked the electrical system and found the battery dead with one cell low on water. Charged battery and replaced in plane. Started engine and alternator charged sixty amps. After recheck of system, continued flight to ann arbor without incident. Suspected cause: stuck voltage regulator. Future action: will activate additional electrical equipment periodically to observe the needle move. When only the radios are active, the current usage is so small that the gauge needle appears to be on zero charge.

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Original NASA ASRS Text

Title: CPR SMA HAD ELECTRICAL PROBLEM FAILURE AT CRUISE ALT.

Narrative: ATC REPORTED THE XPONDER CODE HAD BEEN LOST. AUTOPLT FAILED IMMEDIATELY FOLLOWING. LIGHTS DIMMED. TURNED OFF ALL ELECTRICAL EXCEPT ONE COM SET. CHECKED ALTERNATOR CIRCUIT BREAKER OK, ALTERNATOR SWITCH CYCLED, NO CHANGE. LANDED AT REEDSVILLE ARPT. THE ALTERNATOR WARNING LIGHT NEVER ACTIVATED. THE A&P CHECKED THE ELECTRICAL SYSTEM AND FOUND THE BATTERY DEAD WITH ONE CELL LOW ON WATER. CHARGED BATTERY AND REPLACED IN PLANE. STARTED ENGINE AND ALTERNATOR CHARGED SIXTY AMPS. AFTER RECHECK OF SYSTEM, CONTINUED FLT TO ANN ARBOR WITHOUT INCIDENT. SUSPECTED CAUSE: STUCK VOLTAGE REGULATOR. FUTURE ACTION: WILL ACTIVATE ADDITIONAL ELECTRICAL EQUIPMENT PERIODICALLY TO OBSERVE THE NEEDLE MOVE. WHEN ONLY THE RADIOS ARE ACTIVE, THE CURRENT USAGE IS SO SMALL THAT THE GAUGE NEEDLE APPEARS TO BE ON ZERO CHARGE.

Data retrieved from NASA's ASRS site as of August 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.