FTW04LA142

The 2,919-hour airline transport rated pilot stated that the airplane was climbing through an altitude of 5,500 feet mean sea level (msl) when he heard a "pop" and started to smell something "funny," but there was no visible smoke. He elected to go to the nearest airport and land, and noticed that his push-to-talk button was no longer operative. The pilot set code 7700 in the transponder and began a descent. During the descent, the cockpit began to fill with an "acrid black" smoke, and he saw flames through an opening in the instrument panel. The pilot attempted to suppress the fire with a hand-held fire extinguisher; however, he was unsuccessful. The pilot elected to execute an emergency landing in a field, collided with a barbed wire fence, and the airplane was then consumed by fire. Examination of the airplane's electrical system revealed that the main battery cable that ran between the main power relay and the main power bus was severed approximately two inches from the main bus. There was beading and localized melting on both ends. Under magnification, the damaged areas had an eroded appearance and there was some evidence of pitting. This type of damage is indicative of an electrical arcing event, which most likely ignited the insulation surrounding the main power wiring assembly and spread to other combustible items in the area. The initiating event for the arc could not be determined.

On May 27, 2004, at 1556 central daylight time, a Piper PA-34-200T twin-engine airplane, N2948S, was destroyed during an emergency landing following an in-flight fire near Cleveland, Texas. The commercial pilot, sole occupant of the airplane, sustained minor injuries. The airplane was registered to and operated by the pilot. An instrument flight rules (IFR) flight plan was filed for the personal flight that originated at the Pearland Regional Airport (LVJ), near Houston, Texas, about 1530, and was destined for Palestine Municipal Airport (PSN), near Palestine, Texas. Visual meteorological conditions prevailed for the cross-country flight conducted under 14 Code of Federal Regulations Part 91.

In a telephone interview, the pilot reported that he was climbing through an altitude of 5,500 feet mean sea level (msl) when he heard a "pop" and started to smell something "funny," but there was no visible smoke. He elected to proceed to the nearest airport and land, and noticed that his push-to-talk button was no longer operative. The pilot set code 7700 in the transponder and began a descent. Shortly after, he began to smell smoke and extended the landing gear. As the airplane descended through 5,300 feet, the pilot turned off the master switch and descended at a rate of 1,000 feet per minute. As the airplane descended, the cockpit began to fill with an "acrid black" smoke, and he saw flames through an opening in the instrument panel. The pilot attempted to suppress the fire with a hand-held fire extinguisher; however, he was unsuccessful. He made an emergency landing in a field, collided with a barbed wire fence, and safely exited the airplane, which was later consumed by fire.

The pilot reported that he had the following electrical components turned on when he departed: master switch, panel mounted Garmin 430, all radios, transponder, and the audio panel. The airplane last annual inspection was completed in April 2004, and the only work performed on the electrical system was the replacement of the right hand ammeter. A new battery was also installed in December 2003.

The airplane's electrical system was examined on July 22, 2004, by a Safety Board Fire and Explosion Specialist. The main power wire assembly that ran between the main power relay and the main power buss was severed approximately two inches from the main buss. There was beading and localized melting on both ends. Under magnification, the damaged areas had an eroded appearance and there was some evidence of pitting. This type of damage is indicative of an electrical arcing event.

The arcing event most likely ignited the insulation surrounding the main power wiring assembly and spread to other combustible items in the area. The circuit breaker panel and main power bus were heavily fire damaged. The pilot stated that, after smoke started coming from the circuit breaker panel, the panel began to melt. The aluminum faceplate for the circuit breaker panel was melted and brittle with material missing in places having been consumed in the fire. The circuit breaker switches were mostly consumed in the fire with only the spring remaining in the switch. The few remaining switches were delaminated and brittle. The circuit breakers were brittle with places where the Bakelite covers were chipped and delaminated. Several circuit breakers were unaccounted for. The copper bus bars were intact. The damage to these components are adjacent to the severed portion of the main power wire assembly.

The initiating event for the arc could not be determined. Electric arcing of a conductor can occur when either the conductor's insulation or the conductor is damaged or compromised. While there is no mention of any noticeable damage to the insulation of the wire assembly during the yearly inspection, there was no way to visually inspect the conductor inside the insulation. Since the conductor insulation had melted away as a result of the fire and the conductor was damaged as a result of the arcing event and subsequent fire, there was no way to determine if there was any preexisting damage to either the conductor or the conductor's insulation.

No other area in the main power system demonstrated severe fire or electrical damage. The battery was heavily sooted but otherwise undamaged. The main power relay was heavily sooted and plastic outer components were slightly melted. No anomalies were found in an x-ray of the relay other than uneven surfaces on the coil. According to the manufacturer, the unevenness of the coil is normal and is a result of a manufacturing process. In addition, there have not been any documented cases of this type of relay being involved in a fire event. The relay, when it does fail, tends to fail in the "open" position, which cuts the power off to the main power buss.