INSTRUCTOR PLT OF A C172 DECLARED AN EMER AND DIRECTED HIS INST INSTRUCTOR STUDENT TO RETURN TO LAND AFTER AN ELECTRICAL SMOKE WAS SMELLED COMING FROM THE INST PANEL.

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ON FEB/XA/99; I WAS GIVING FLT INSTRUCTION TO A CFII CANDIDATE. IN ORDER TO PROVIDE REALISTIC DISTR AND SIMULATE AS CLOSELY AS POSSIBLE A REAL EMER; I PULLED THE ALTERNATOR CIRCUIT BREAKER SHORTLY AFTER START-UP. AFTER ABOUT 1/2 HR OF FLYING AROUND DOING INST WORK; THE STUDENT NOTICED THE RADIOS BLINK OFF/ON. HE QUICKLY SURVEYED THE BREAKER PANEL TO NOTICE THE CIRCUIT BREAKER POPPED (ACTUALLY PULLED BY ME) AND WE HAD A DISCUSSION ABOUT CHKING EVERY SO OFTEN; THE ELECTRICAL SYS. WELL DONE. I PUSHED THE CIRCUIT BREAKER BACK IN. AS WE STARTED TO SET UP FOR AN ILS TO RWY 14 AT CXO; WE NOTICED THE ALTERNATOR CIRCUIT BREAKER WAS POPPED (ABOUT 2 MINS ELAPSED TIME SINCE I PUSHED IT IN). SINCE IT POPPED FOR REAL; WE DECIDED IT WOULD BE BEST TO USE THE CHKLIST. SO WE PULLED OUT THE POH AND EXECUTED THE CHKLIST FOR 'LOW VOLTAGE' SINCE THE AMMETER INDICATED A DISCHARGE. UPON COMPLETION OF THE CHKLIST AND RESETTING OF THE CIRCUIT BREAKER; WE IMMEDIATELY SMELLED WHAT WE PERCEIVED BURNING INSULATION OR SOMETHING ELECTRICAL. WE IMMEDIATELY BEGAN TO SHUT DOWN ELECTRICAL EQUIP AND PULLED THE CIRCUIT BREAKER BACK OUT. AT THIS POINT; WE COULD NOT SEE ANY SMOKE VISIBLE; BUT THE BURNING SMELL WAS STRONG AND DEFINITE. WE DEDUCED THAT SOMETHING WAS PROBABLY SMOLDERING AND ABOUT TO CATCH FIRE SO WE SQUAWKED 7700 AND DECLARED AN EMER ON 122.95 (CXO CTAF) TO CLR OTHER ACFT OUT OF THEIR PATTERN. NOT WANTING TO LEAVE THE ELECTRICAL SYS ON; WE DECIDED TO SHUT THE MASTER SWITCH OFF. WE TURNED ON THE RADIO ONLY TO RPT 10 MI; 5 MI AND 1 MI FINAL. TURNING THE MASTER ON WOULD CAUSE THE SMELL AGAIN. WE LANDED ON THE XWIND RWY 14 AND TAXIED TO THE TERMINAL TO BE MET BY FIRE TRUCKS; EMS; AND LCL POLICE. EVERYONE SEEMED DISAPPOINTED THAT THERE WAS NO GREAT AMOUNT OF SMOKE BILLOWING FROM THE COCKPIT AND WONDERED WHY WE DECLARED AN EMER. AFTER GIVING OUR NAMES; ADDRESSES AND PHONE NUMBERS TO THE LCL CREW; WE FOUND A MECH WHO MIGHT BE ABLE TO DIAGNOSE (OR AT LEAST CONFIRM OR DENY) OUR CLAIMS OF SOMETHING BURNING IN THE ACFT. THE MECH GOT INTO THE ACFT; TURNED THE MASTER SWITCH ON; AND IMMEDIATELY TURNED IT OFF. HE SAID THERE WAS SMOKE COMING FROM THE AREA NEAR THE TURN COORDINATOR. (AT LEAST WE WERE JUSTIFIED IN DECLARING OUR EMER.) MY BOSS OF ACR X FBO X WANTED US TO FLY THE ACFT BACK TO DWH (APPROX 15 MI SW CXO OVER NOTHING BUT WOODED AREA). OBVIOUSLY WE WERE RELUCTANT TO DO SO AND WERE GLAD THAT THE MECH SAID THE ACFT WAS 'NO-FLY' STATUS UNTIL HE CHKED IT OUT. AFTER AN INSPECTION; THE MECH DEDUCED THAT A SHORT MAY HAVE DISABLED THE ALTERNATOR. HE SAID IT WOULD BE SAFE TO FLY HOME ON BATTERY PWR. SINCE DWH IS A CLASS D ARPT; WE MADE ARRANGEMENTS TO COME IN NORDO AND RECEIVE LIGHT GUN SIGNALS. WE LANDED UNEVENTFULLY AND TAXIED THE ACFT TO OUR MAINT FOLKS; FBO MECH. WE LATER FOUND THAT THE ALTERNATOR CONTRA UNIT (VOLTAGE REGULATOR) HAD BURNED UP. IN RETROSPECT; I DON'T THINK WE DID ANYTHING WRONG; BUT WE PROBABLY DIDN'T HAVE TO DECLARE AN EMER. AS AN INSTRUCTOR; I ALWAYS STRIVE TO BE CONSERVATIVE FIGURING IT'S BETTER TO BE SAFE THAN SORRY. I DO WISH; HOWEVER; THAT CESSNA; PIPER; BEECH; ETC; WOULD BE FORCED (THROUGH AIRWORTHINESS DIRECTIVES) TO PUT FIRE EXTINGUISHERS IN THESE ACFT.