Narrative:

Recurrency being given to a multi-commercial instrument rated pilot. Climbed to 4000 ft above the beach training area (approximately 10 NM south of chawktaw nolf). Performed air work and then failed left engine (pulled mixture lever). Student executed bold face procedures and secured engine uneventfully. Started the restart checklist when we selected the left starter to turn the engine over, all electrical system failed, released the switch and system returned. No rotation on engine. Informed pns that we were single engine and began a slow descent into the milton pattern (from the south). Winds were favoring runway 18. Entered an extended right downwind for runway 18 at milton (2r4).upon turning base to final, we selected gear down -- once again total electrical failure. Told student and assisted him in executing a single engine go around (no communications) with the intention of doing a manual gear extension then returning to land. When passing through 600 ft MSL (approximately 500 ft AGL) noted a very faint gear down indicator. Soon thereafter, a bright and steady gear down indication appeared and the electrical system returned. Aircraft stabilized at 700 ft MSL and we elected to leave gear down for fear it would freeze midway up if it came up at all. I elected to accept a tailwind landing and we performed a slow teardrop turn back toward runway 36. Landing was uneventful. Upon inspection, corroded battery terminals were found. Told student that he performed exceptionally well utilizing CRM concepts (I was an flight engineer on a 6-MAN helicopter crew for 11 yrs). I discovered after speaking with a mechanic that an aircraft's alternators, once excited, still rely on the battery to continue excitation, unlike an automobile they are not self-sustaining once excited. Simplistically it makes sense, but from a safety standpoint it seems like the battery is relied upon too much in the electrical system.

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Original NASA ASRS Text

Title: A PIPER 30 AT 4000 FT LOST ALL ELECTRICAL SYS WHEN LOADING THE BATTERY BY ENG STARTER OR LNDG GEAR OP CAUSED BY CORRODED BATTERY TERMINALS.

Narrative: RECURRENCY BEING GIVEN TO A MULTI-COMMERCIAL INST RATED PLT. CLBED TO 4000 FT ABOVE THE BEACH TRAINING AREA (APPROX 10 NM S OF CHAWKTAW NOLF). PERFORMED AIR WORK AND THEN FAILED L ENG (PULLED MIXTURE LEVER). STUDENT EXECUTED BOLD FACE PROCS AND SECURED ENG UNEVENTFULLY. STARTED THE RESTART CHKLIST WHEN WE SELECTED THE L STARTER TO TURN THE ENG OVER, ALL ELECTRICAL SYS FAILED, RELEASED THE SWITCH AND SYS RETURNED. NO ROTATION ON ENG. INFORMED PNS THAT WE WERE SINGLE ENG AND BEGAN A SLOW DSCNT INTO THE MILTON PATTERN (FROM THE S). WINDS WERE FAVORING RWY 18. ENTERED AN EXTENDED R DOWNWIND FOR RWY 18 AT MILTON (2R4).UPON TURNING BASE TO FINAL, WE SELECTED GEAR DOWN -- ONCE AGAIN TOTAL ELECTRICAL FAILURE. TOLD STUDENT AND ASSISTED HIM IN EXECUTING A SINGLE ENG GAR (NO COMS) WITH THE INTENTION OF DOING A MANUAL GEAR EXTENSION THEN RETURNING TO LAND. WHEN PASSING THROUGH 600 FT MSL (APPROX 500 FT AGL) NOTED A VERY FAINT GEAR DOWN INDICATOR. SOON THEREAFTER, A BRIGHT AND STEADY GEAR DOWN INDICATION APPEARED AND THE ELECTRICAL SYS RETURNED. ACFT STABILIZED AT 700 FT MSL AND WE ELECTED TO LEAVE GEAR DOWN FOR FEAR IT WOULD FREEZE MIDWAY UP IF IT CAME UP AT ALL. I ELECTED TO ACCEPT A TAILWIND LNDG AND WE PERFORMED A SLOW TEARDROP TURN BACK TOWARD RWY 36. LNDG WAS UNEVENTFUL. UPON INSPECTION, CORRODED BATTERY TERMINALS WERE FOUND. TOLD STUDENT THAT HE PERFORMED EXCEPTIONALLY WELL UTILIZING CRM CONCEPTS (I WAS AN FE ON A 6-MAN HELI CREW FOR 11 YRS). I DISCOVERED AFTER SPEAKING WITH A MECH THAT AN ACFT'S ALTERNATORS, ONCE EXCITED, STILL RELY ON THE BATTERY TO CONTINUE EXCITATION, UNLIKE AN AUTOMOBILE THEY ARE NOT SELF-SUSTAINING ONCE EXCITED. SIMPLISTICALLY IT MAKES SENSE, BUT FROM A SAFETY STANDPOINT IT SEEMS LIKE THE BATTERY IS RELIED UPON TOO MUCH IN THE ELECTRICAL SYS.

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.