N3416TCessna 177 · 1967

On September 24, 2015, about 1515 Pacific daylight time, a Cessna 177 Cardinal, N3416T, experienced an on-ground fire while the pilot attempted to start the engine at the Jacqueline Cochran Regional Airport, Thermal, California. The owner, who was additionally the passenger, was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The private pilot and passenger were not injured; the airplane sustained substantial damage. The cross-country personal flight was to originate from Thermal with a planned destination of Boulder Municipal Airport, Colorado. Visual meteorological conditions prevailed and no flight plan was filed.The pilot reported that the airplane was based out of Boulder, Colorado and earlier in the morning, he and his passenger completed a flight from there to Palm Springs, California. They departed from Palm Springs and landed in Thermal with the intent of purchasing fuel at the airport. He shut the engine down and then decided not to get fuel at that location on the field. He started the engine and then moved to the other side of the field. At that point, they topped off the wing tanks with 25 gallons.

After fueling, the pilot attempted to start the engine however it would not turn over. With the mixture in the full rich position he then pumped the primer once and continued to crank the engine. They observed a fire start in the muffler area. He proceeded to crank the starter in an attempt to suck the fire through the muffler. The passenger egressed the airplane and discharged the entire contents of a fire extinguisher on board. The pilot exited out of the rear of the airplane. At no time did the engine actually start and the propeller was not turning. The pilot noted that the engine was running very hot that day as seen from the oil temperature gauge. He thought this was due to the outside air temperatures reaching over 100 degrees Fahrenheit and the duration of the flight.

A certified airframe and powerplant mechanic (A&P) completed a post-accident teardown examination under the auspice of Federal Aviation Administration (FAA) inspectors. Fuel system continuity was established from the firewall to each of the engine's cylinders. The boost pump was activated with no anomalies noted. Removal of the spark plugs revealed that all were uniformly dark in color an indication of an oil fouled operating condition however a compression check revealed normal operations. The cylinders' combustion chambers were examined through the upper spark plug holes utilizing a lighted borescope. The combustion chambers remained mechanically undamaged, and there was no evidence of foreign object ingestion or detonation. There was no evidence of valve to piston face contact observed. The gas path and combustion signatures observed at the spark plugs, combustion chambers, and exhaust system components displayed coloration that was consistent with a rich operation. There was no oil residue observed in the exhaust system gas path.

The fire appeared to have started on the lower right side of the engine where there was white coloration and excessive heat damage to the firewall and belly skin in that area. The mechanic opined that the source of fuel that ignited the fire was likely due to the pilot over priming the induction system which would have filled the carburetor air box with fuel located in that position.

According to the airframe Pilot's Operating Handbook, "No priming is required when the weather is warm," and that "weak intermittent firing followed by puffs of black smoke from the exhaust stack indicates over-priming or flooding." It further states that "excess fuel can be cleared from the combustion chambers by the following procedure: Set the mixture control full lean and the throttle full open; then crank the engine through several revolutions with the starter," and to "repeat the starting procedure without any additional priming."