DIVERSION TO ALTERNATE REQUIRED IN A NIGHT OP WHEN A C- 172 HAS A PRIMARY ELECTRICAL SUPPLY PROB.

Narrative

I WAS GIVING THE LAST DUAL NIGHT FLT TO A STUDENT PLT. AFTER TKOF THE LIGHTS STARTED TO DIM. I WAS ABOUT 20 MI FROM OUR ARPT; PRACTICING LNDGS AT AN ARPT WHICH IS NORMALLY CLASS D; YET CLOSED AT XX00PM AND WAS NOW CLASS E DOWN TO 700 FT AGL. AFTER THE LIGHTS STARTED TO DIM I ASKED THE STUDENT IF HE HAD TURNED THEM DOWN; HE REPLIED 'NO.' I THEN TOOK OVER THE CTLS AND STARTED TO CHK THE AMP METER; IT INDICATED 0 CHARGE OR DISCHARGE. I TRIED RECYCLING THE MASTER; TRIED JUST RUNNING ON THE BATTERY; THEN JUST THE ALTERNATOR. NO RESPONSE. DURING THIS TIME I HAD MADE A BROKEN; PARTIAL CONTACT WITH KALAMAZOO APCH; THEY REPLIED THAT THEY WERE NOT RECEIVING MY XPONDER. I DECIDED TO TURN BACK TO THE UNCTLED ARPT WHERE I KNEW THERE WAS VERY LITTLE TO NO TFC (IN KALAMAZOO THERE WAS NUMEROUS TFC; AND I ALSO HAD NO WAY OF INDICATING THAT I NEEDED LIGHT GUN SIGNALS). I WENT BACK TO BATTLE CREEK; I WAS TRYING TO ISOLATE THE PROB WITHOUT ANY SUCCESS. I TOOK OUT THE POH AND FOLLOWED THE PROCS WHICH ENDED WITH LNDG AS SOON AS PRACTICAL. AT THIS POINT I LOST ALL ELECTRICAL. I WENT DOWNWIND; BASE; FINAL. ON FINAL; WITH MY STUDENT HOLDING OUR FLASHLIGHT ON THE AIRSPD INDICATOR; THE LIGHTS ON THE RWY WENT TO ALMOST COMPLETELY OFF. I THEN DID MY BEST IN MY ATTEMPT TO LAND AND TAXI OFF. I THOUGHT THAT THE LIGHTS ON THE RWY WENT COMPLETELY OFF; YET I HAD NO WAY TO TURN THEM BACK ON. AFTER REPAIRS WERE MADE ON THE AIRPLANE; IT WAS FOUND THAT THE VOLTAGE REGULATOR HAD FAILED.