PLT DISTR SMOKE IN COCKPIT. RETURN LAND. UNAUTH PENETRATION OF AIRSPACE; PROX OF TCA.

Narrative

WAS PRACTICING SOLO AEROBATIC FLT IN AN AREA BTWN 2000- 5000 FT AGL; GREATER THAN 4 NM OFF OF THE NEAREST AIRWAY JUST OUTSIDE THE ESE BOUNDARY OF THE TAMPA CLASS B AIRSPACE. WHILE IN THE PROCESS OF RECOVERING FROM A NORMAL SPIN (APPROX 2000 FT AGL) NOTICED A PUNGENT AROMA IN COCKPIT AND LOOKED DOWN AT THE RADIO STACK (MOUNTED NEAR THE FLOOR BTWN REAR PLT'S LEGS). THE WIRING HARNESS (RUNNING FROM UNDER THE REAR PANEL DOWN TO THE RADIO STACK) WAS SMOKING BADLY; AN OBVIOUS MALFUNCTION. I IMMEDIATELY TURNED OFF THE MASTER AND ALTERNATOR FIELDS AND ATTEMPTED TO VENT THE CABIN. BECAUSE I WAS ABLE TO VENT THE CABIN AND BECAUSE THE ENG WAS RUNNING NORMALLY I DECIDED AGAINST AN EMER LNDG BELOW. BUT MY BIGGEST CONCERN WAS THE POSSIBILITY OF SHORTING BEHIND THE PANEL AND SUBSEQUENT ACFT FIRE. (THIS IS OF EXTREME SIGNIFICANCE IN A COTTON FABRIC COVERED ACFT.) I QUICKLY DECIDED TO LAND EITHER AT LAKELAND ARPT OR RETURN TO PETER O. KNIGHT. I DECIDED ON PETER O. KNIGHT FOR THE FOLLOWING REASONS: 1) I WAS FAMILIAR WITH THE RTE AND KNEW I COULD AVOID ANY POPULATED AREAS GOING BACK; ALSO THE LAST 5-6 NM COULD BE FLOWN OVER TAMPA BAY IN CASE OF EMER BAILOUT (WAS WEARING CHUTE). 2) PETER O. KNIGHT IS FAR LESS BUSY; IS UNCTLED; AND ACCESSIBLE WITHOUT PENETRATING CLASS B OR CLASS D AIRSPACE; UNLIKE LAKELAND. IN SHORT; I WAS TOTALLY UNFAMILIAR WITH LAKELAND AND ITS SURROUNDING SUBURBAN AREAS. I WAS AWARE OF THE RETURNING RTE TO PETER O. KNIGHT; OF SEVERAL POTENTIAL EMER FIELDS ENRTE; AND FELT THAT I COULD SAFETY STAY BELOW CLASS B AIRSPACE; AVOID ANY POSSIBLE ACFT IN THE PATTERN; WHILE WITHOUT RADIO/XPONDER/ELECTRICAL SYS. AS PIC I DECIDED I COULD MORE SAFELY RETURN TO O. KNIGHT AND THAT RTE WOULD OFFER MORE CONTINGENCIES TO MINIMIZE DANGER TO ME OR ANYBODY ON THE GND; AND THAT SAFE RESOLUTION OF MY EMER FAR OUTWEIGHED VIOLATING THE MODE C VEIL; ESPECIALLY SINCE I WOULD NOT HAVE TO ENTER CLASS B AIRSPACE. I DECIDED THAT TURNING ON THE MASTER TO TRY AND SEE IF I COULD RAISE TPA APCH AND DECLARE AN EMER WOULD INCREASE THE RISK OF FIRE IN THE ACFT. I DSNDED TO 1000 FT AND FLEW BACK TO PETER O. KNIGHT AND MADE A NORMAL APCH AND LNDG. SINCE A SAFE RESOLUTION AND SAFE LNDG IS THE MOST IMPORTANT GOAL IN AN EMER; I BELIEVE I ACTED RESPONSIBLY; ESPECIALLY WHERE THE CHOSEN RTE OFFERED MORE CONTINGENCY SUPPORT AND A GREATER CHANCE FOR SAFE RESOLUTION. SUBSEQUENT REPAIR EXAMINATION SHOWED THAT IN THE PAST 5 YRS THE WIRE BUNDLE HAD STARTED CHAFING AGAINST THE TOP EDGE OF THE RADIO PANEL AND HAD FINALLY CHAFED THROUGH THE INSULATION; SHORTING 120 TO GND. THE SHORTING TOOK PLACE BTWN THE BATTERY AND THE BREAKER; MOUNTED IN THE RADIO PANEL.