On August 1, 2009, about 1350 mountain daylight time, an experimental built Gray RV-6, N69KG, was destroyed following impact with terrain near the Caldwell Industrial Airport (EUL), Caldwell, Idaho. The private pilot, the sole occupant, was killed. Visual meteorological conditions prevailed for the local flight, which was conducted in accordance with 14 Code of Federal Regulations (CFR) Part 91, and a flight plan was not filed. The flight was originating at the time of the accident. According to a witness who was positioned about midfield on the airport, he observed a tan colored with blue trim RV-6 type aircraft depart Runway 12. The witness stated that as the airplane passed him at an altitude of about 100 to 200 feet [above ground level] (agl), "…the engine of the plane began to make a 'popping' noise." The witness reported that a few seconds later the aircraft turned onto a left crosswind, then "quickly" to downwind at an altitude of about 200 feet [agl]. The witness further reported that as the airplane continued on downwind "…the nose of the RV was increasing its pitch and it was apparent that the RV was not climbing. As the RV came approximately abeam the number 12 on its left downwind, it made a steep left turn as to land on 12. As this occurred the nose of the RV dropped, and within a few seconds I saw it dive into the ground and erupt into flames." Prior to impact the airplane had collided with a set of power lines, which bordered the airport on its north perimeter. The airplane was consumed by the post impact fire. A Federal Aviation Administration (FAA) aviation safety inspector who examined the accident site reported that the airplane came to rest in an upright position next to an airport perimeter fence and inside airport property. The accident site was located about 700 feet northeast of the approach end of Runway 12. The fuselage, empennage, and engine were all located together at the main impact site. Due to impact forces and thermal damage, control continuity could not be confirmed. There were no observed anomalies with the airframe when examined at the accident site. The airplane's engine was examined under the supervision of the FAA inspector by a certificated airframe and powerplant mechanic. The examination revealed no anomalies with the cylinders or the valve train as a result of a borescope inspection. Additionally, no stuck valves were observed. The examination also revealed that all spark plugs were found to have excessive gaps from .028 - .030; the manufacturer recommends .016 - .021. All but one spark plug failed a bench check when exposed to pressures above 80 psi. During the examination, the oil filter was cut and inspected with an acceptable amount of trace particulate matter noted. According to the FAA inspector, a family member reported that the airplane had set idle for about a year on the airport ramp and had not been flown. The family member stated that about a week prior to the accident flight [the pilot] flew it [the airplane] around the airport traffic pattern. The family member further revealed that on the morning of the accident flight [the pilot] removed the spark plugs, sandblasted them, checked [cylinder] compression, and removed the air filter. The family member reported, "The filter had 'goop' on it. [The pilot] cleaned it around noon before the accident." No aircraft, engine or pilot logbooks were located during the investigation. An autopsy was performed on the pilot at the Ada County Coroner's Office, Boise, Idaho, on August 3, 2009. According to the autopsy report the cause of death was "…Carbon monoxide poisoning and thermal injuries." The FAA's Forensic Toxicology Research Section, Oklahoma City, Oklahoma, performed postmortem toxicology of specimens from the pilot. The specimens were negative for cyanide, ethanol, and drugs. The results also revealed 28 percent carbon monoxide was detected in the blood.