Narrative:

I was flying at 9000 ft on an IFR flight plan, ryy to roa. Roa is my home field, but I've been on an extended business trip for several months near ryy. It was very clear and smooth on this night. I thought I smelled a whiff of smoke, but couldn't identify it so I declared an emergency and asked to divert to hky which was about 5 mi to the right of my current track. ZTL cleared me direct to hky and handed me off to the tower which cleared me to land on any runway. Landed runway 24 without incident. I did not notice any further indication of smoke while diverting to hky, during landing or taxi. Taxied to the FBO, shut down and filled out the fireman's paperwork. The FBO lineman helped push the airplane into an open hangar with some lighting. I removed the cowling and inspected all the hoses and wiring for leaks or looseness or signs of anything that might cause a smoke smell and found nothing. Replaced the cowling, performed a run-up and a system check of each component. Found no anomalies, no evidence of smoke. All equipment appeared correct. Spent the night, and from my hotel, called my mechanic to discuss what further checks might be appropriate. Next morning I hiked to the hardware store and purchased a voltmeter to check for over or under voltage on the aircraft. Returned to the FBO, removed the cowling and reexamined all wiring and hoses and battery, but found no anomalies or evidence of smoke. Replaced cowling, performed a run-up and tried each system individually and together. All equipment appeared correct and functional. Checked voltage at cigarette lighter and found it to be correct at idle and run-up. No evidence of smoke or smoke odor was found. Decided that aircraft was safe to fly, so continued on to roa. My mechanic pulled the alternator and found the battery terminal to be burned about halfway through from arcing. This had been 'examined and corrected' by a mechanic at ryy a few weeks earlier with no mention of a burned terminal. I don't know if it burned further during this flight. I presume that, since PIC is the final authority/authorized on the safe outcome of the flight, if a mechanic at hky should have been called to examine the aircraft prior to continuing on to roa. It was friday night and a mechanic would next be available on monday. Also, would the mechanic at hky be any better than the mechanic at ryy? There is value in finding a mechanic, who knows your airplane and earns your trust.

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Original NASA ASRS Text

Title: A C172 PLT SMELLS SMOKE INFLT RESULTING IN AN EMER LNDG.

Narrative: I WAS FLYING AT 9000 FT ON AN IFR FLT PLAN, RYY TO ROA. ROA IS MY HOME FIELD, BUT I'VE BEEN ON AN EXTENDED BUSINESS TRIP FOR SEVERAL MONTHS NEAR RYY. IT WAS VERY CLR AND SMOOTH ON THIS NIGHT. I THOUGHT I SMELLED A WHIFF OF SMOKE, BUT COULDN'T IDENT IT SO I DECLARED AN EMER AND ASKED TO DIVERT TO HKY WHICH WAS ABOUT 5 MI TO THE R OF MY CURRENT TRACK. ZTL CLRED ME DIRECT TO HKY AND HANDED ME OFF TO THE TWR WHICH CLRED ME TO LAND ON ANY RWY. LANDED RWY 24 WITHOUT INCIDENT. I DID NOT NOTICE ANY FURTHER INDICATION OF SMOKE WHILE DIVERTING TO HKY, DURING LNDG OR TAXI. TAXIED TO THE FBO, SHUT DOWN AND FILLED OUT THE FIREMAN'S PAPERWORK. THE FBO LINEMAN HELPED PUSH THE AIRPLANE INTO AN OPEN HANGAR WITH SOME LIGHTING. I REMOVED THE COWLING AND INSPECTED ALL THE HOSES AND WIRING FOR LEAKS OR LOOSENESS OR SIGNS OF ANYTHING THAT MIGHT CAUSE A SMOKE SMELL AND FOUND NOTHING. REPLACED THE COWLING, PERFORMED A RUN-UP AND A SYS CHK OF EACH COMPONENT. FOUND NO ANOMALIES, NO EVIDENCE OF SMOKE. ALL EQUIP APPEARED CORRECT. SPENT THE NIGHT, AND FROM MY HOTEL, CALLED MY MECH TO DISCUSS WHAT FURTHER CHKS MIGHT BE APPROPRIATE. NEXT MORNING I HIKED TO THE HARDWARE STORE AND PURCHASED A VOLTMETER TO CHK FOR OVER OR UNDER VOLTAGE ON THE ACFT. RETURNED TO THE FBO, REMOVED THE COWLING AND REEXAMINED ALL WIRING AND HOSES AND BATTERY, BUT FOUND NO ANOMALIES OR EVIDENCE OF SMOKE. REPLACED COWLING, PERFORMED A RUN-UP AND TRIED EACH SYS INDIVIDUALLY AND TOGETHER. ALL EQUIP APPEARED CORRECT AND FUNCTIONAL. CHKED VOLTAGE AT CIGARETTE LIGHTER AND FOUND IT TO BE CORRECT AT IDLE AND RUN-UP. NO EVIDENCE OF SMOKE OR SMOKE ODOR WAS FOUND. DECIDED THAT ACFT WAS SAFE TO FLY, SO CONTINUED ON TO ROA. MY MECH PULLED THE ALTERNATOR AND FOUND THE BATTERY TERMINAL TO BE BURNED ABOUT HALFWAY THROUGH FROM ARCING. THIS HAD BEEN 'EXAMINED AND CORRECTED' BY A MECH AT RYY A FEW WKS EARLIER WITH NO MENTION OF A BURNED TERMINAL. I DON'T KNOW IF IT BURNED FURTHER DURING THIS FLT. I PRESUME THAT, SINCE PIC IS THE FINAL AUTH ON THE SAFE OUTCOME OF THE FLT, IF A MECH AT HKY SHOULD HAVE BEEN CALLED TO EXAMINE THE ACFT PRIOR TO CONTINUING ON TO ROA. IT WAS FRIDAY NIGHT AND A MECH WOULD NEXT BE AVAILABLE ON MONDAY. ALSO, WOULD THE MECH AT HKY BE ANY BETTER THAN THE MECH AT RYY? THERE IS VALUE IN FINDING A MECH, WHO KNOWS YOUR AIRPLANE AND EARNS YOUR TRUST.

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.