NTSB Factual Report

On August 23, 2002, at 1020 mountain standard time, the pilot of a Cessna 172N, N4796E, aborted the takeoff from runway 4R at Falcon Field Airport (FFZ), Mesa, Arizona, after he observed smoke in the cockpit. Professional Flight Instruction Services operated the airplane under the provisions of 14 CFR Part 91. The ensuing post-impact fire destroyed the airplane. The certified flight instructor (CFI) and student pilot were not injured. Visual meteorological conditions prevailed for the local area training flight and no flight plan had been filed.

According to the CFI, prior to the takeoff roll, they did a final check of the systems with no abnormal conditions noted. There were no discrepancies noted with the takeoff roll or takeoff climb out. About 5-10 seconds later, the student yelled "fire," and the CFI saw smoke "billowing out from under the dash, just left of the throttle." He did not see any sparks. At that point the CFI took the flight controls, reduced the power, and landed straight ahead "as rapidly as possible" on the remaining runway. He stated that he observed that the landing light circuit breaker had popped. He made an unsuccessful attempt to reset the circuit breaker before noticing flames coming from the instrument panel. After landing, he applied the brakes to stop on the runway; however, he saw they were not going to be able to stop, so he maintained directional control of the airplane and kept braking until the airplane came to a stop. Prior to exiting the airplane, he turned off the avionics master, pulled the mixture to idle cutoff, turned off the fuel selector, magnetos, and the master switch. After they exited, he didn't see any more smoke or flames; however, in about a minute, he saw flames emanating from the original area.

According to the student pilot, they had been cleared for takeoff, and rotated about halfway down the runway. The airplane was about 100 feet above the ground when he noticed sparks and smoke coming from the instrument panel near the circuit beakers and throttle. He told his CFI there was a fire in the cockpit. The CFI reduced the power and landed the airplane on the remaining runway. The student pilot stated that due to the airplane's speed, it overran the runway and went into an open area off the runway. After they exited the airplane, a small fire ignited behind the dash, but they were not able to extinguish the fire. By the time the fire crew arrived the airplane was completely engulfed in flames. The student pilot confirmed that the CFI shut down the fuel, master and magneto switches, and the electrical. He stated that the CFI was not able to turn off the landing light switch, and that the circuit breaker for the landing light had been "tripped."

A Federal Aviation Administration (FAA) airworthiness inspector responded to the accident site. He noted that the cockpit area of the airplane had completely burned away, with only the floorboards remaining. The left wing also sustained fire damage.

On October 3-4, 2002, the airplane was examined at Air Transport, Phoenix, Arizona, under the auspices of the National Transportation Safety Board. Also present was a representative from Cessna Aircraft Company, a party to the investigation. Investigators noted that the fire had destroyed the entire cockpit/instrument panel and the majority of the instruments were rendered unidentifiable. The six circuit breakers from the Avionics bus, and nine of the eleven circuit breakers from the Primary bus were located. However, investigators were not able to identify the 20-ampere landing light circuit breaker. One circuit breaker, identified as the alternator circuit breaker, was in the tripped position. The avionics master switch was in the OFF position. Investigators noted that the wires from the circuit breakers to the avionics and instruments were burned, melted, and/or broken. The majority of the fire damage was noted on the left side of the airplane. The airframe manufacturer indicated that the landing light wires are all 16-gage, and that the landing light circuit breaker is not a shared circuit breaker.

The manufacturer's representative noted that the circuit breaker that had been "tripped" was the 60-ampere alternator circuit breaker. The encoder backing plate had a wire bundle, which had several of the 22-gauge wire ends that were beaded, and two of the wires appeared to be soldered together and were brittle. The representative indicated that none of the other avionics instruments exhibited any wire beading.

The encoder backing plate and associated wires were shipped to the Safety Board's metallurgical laboratory in Washington, D.C. The Safety Board's fire and explosion specialist examined the component and wires, and reported that the beading present on the wires was indicative of there being power to those wires at the time of the fire. The wires showed no signs of arcing.

AIRCRAFT INFORMATION

The airplane was a 1978 Cessna 172N, serial number 1727661. A review of the airplane's logbooks revealed a total airframe time of 5,716.5 hours at the last inspection. An annual inspection was completed on December 22, 2001. The operator reported that the last maintenance performed was a 100-hour inspection completed on July 9, 2002, at an estimated airframe total time of 6,000 hours, with 87 hours flown since the last inspection. An aircraft logbook entry date of July 4, 1999, indicated a Garmin GMA 340 Audio Marker panel and Troll FN-200 Avionics fan installation. Also recorded in the July 1999, entry was the removal, "bench test aligned and/or repaired both RT-385A NAV/Coms and Nav Indicators." The logbook entry dated December 22, 2001, also indicated that airworthiness directives #87-20-03R2, 93-05-06, 80-04-03R2 and 2001-23-03 (electrical short-Map Light) were complied with. There were no further logbook entries made available.

In the manufacturer's Information Manual for the airplane, under section 3 titled Emergency Procedures, if an electrical fire is encountered in flight, the pilot should turn off the following items:

Master Switch

Avionics Power Switch

All Other Switches (except the ignition switch)

The vents/cabin air/heat should be CLOSED, and the fire extinguisher, if available, should be activated.

The manufacturer also issues a Pilot Safety and Warning Supplements. In the section titled In-Flight Fires under System Operational Considerations, the manufacturer indicates that in the event of an electrical fire, the pilot should attempt to identify and isolate where the fire is coming from. If the source and location are not readily identifiable and "flight conditions permit," the pilot should turn off the battery/master switch and alternator switch(es) to remove possible sources of the fire.

NTSB Probable Cause

An electrical fire of unknown origin centered near the circuit breaker/throttle area of the instrument panel.