On October 16, 2012, about 0820 central daylight time, an experimental amateur-built Sonex, N198PC, was substantially damaged when it impacted terrain shortly after takeoff from Crossville Memorial Airport (CSV), Crossville, Tennessee. The certificated private pilot/owner and the passenger were seriously injured. Visual meteorological conditions prevailed, and no flight plan was filed for the flight, which was presumed to be destined for Winter Haven’s Gilbert Airport (GIF), Winter Haven, Florida. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. According to personnel from a fixed based operator (FBO) located at Martin Campbell Field (1A3), Copperhill, Tennessee, the pilot and passenger arrived in the accident airplane at their facility on October 12. The pilot stated that they were enroute to a fly-in event at CSV, but had to divert to 1A3 due to deteriorating weather conditions. The following morning, the FBO personnel watched as the pilot taxied the airplane for departure and noted that as the airplane approached the runway, the engine “stopped.” The personnel listened as the pilot then re-started the engine, back-taxied down the runway, and departed without further incident. On the morning of the accident flight, a pilot-rated witness observed as the accident airplane attempted to depart from runway 26 at CSV. The witness stated that he heard the airplane’s engine increase in power, and then heard a sudden reduction of power that caused him to turn his attention toward the airplane. He then observed the airplane about 1,000 feet from the approach end of the runway at an altitude of about 15 feet. The airplane continued to fly at that altitude until about the mid-field point, when the engine power again increased and the airplane “climbed abruptly,” before disappearing from view. The witness walked further out on the flight line in an attempt to regain sight of the airplane, but was advised by other individuals on the airport that the airplane had crashed near the departure end of runway 26, outside of the airport perimeter fence. Another witness, who was driving on a road adjacent to the airport, observed the accident airplane in a tail-low attitude before it began to “spin around” about 2 or 3 times. The airplane then impacted the ground, and the witness stopped to contact local authorities and render assistance. Another witness who stopped to render assistance noted that the pilot had been partially ejected from the cockpit, and did not appear to have been wearing any restraints. A Federal Aviation Administration (FAA) inspector examined the wreckage following the accident. According to the inspector, the airplane impacted terrain beyond the departure end of the runway, in a ravine. The left and right wing roots displayed compression buckling at their aft and forward fuselage connection points, respectively. The outboard leading edge of the left wing leading edge displayed aft crush damage. The propeller was fragmented consistent with ground contact. The fuselage remained intact, with the majority of the damage concentrated within the area of the engine and firewall. A hole approximately 12 inches in diameter was broken through top of the overhead cockpit canopy. The left side of the left seat restraint was found tucked inside a side wall pocket. Continuity of the engine valvetrain and powertrain were confirmed, and rotation of the engine utilizing the starter showed no binding or other faults. Operation of the ignition system to the bottom spark plugs was confirmed, though operation of the top spark plugs could not be confirmed as the required engine speed could not be attained. The spark plugs appeared to be in new condition. Examination of the fuel system showed that fuel was available to the engine, with no anomalies noted. An electronic flight instrument system was recovered from the airplane and forwarded to the NTSB Vehicle Recorder Laboratory for further examination. Power was applied to the intact unit; however, no data were present as the data recording feature had not been enabled. A review of maintenance records revealed that the pilot was also the builder of the experimental amateur-built, kit airplane, which was completed in June 2011. Between that time and October 4, 2012, when the most recent airframe log entry was made, the airplane had accumulated 60 hours of flight time. The airplane’s most recent condition inspection was completed by the pilot in June 2012, at 59 total flight hours. Airman records retained by the FAA showed that the pilot held a private pilot certificate with a rating for airplane single engine land, as well as a repairman experimental aircraft builder certificate for the accident airplane. The pilot’s most recent third-class medical certificate was issued in August 2011, and at that time the pilot reported 525 total hours of flight experience. No further records of the pilot’s flight experience were available for review; however, all of the flight hours recorded in the airframe maintenance log were recorded by the pilot. Crossville Memorial Airport was comprised of a single asphalt runway oriented in an 8/26 configuration. The runway was 5,418 feet long by 100 feet wide. The weather conditions reported at CSV, at 0853, included clear skies, calm winds, temperature 11 degrees Celsius (C), dew point 8 degrees C, and an altimeter setting of 30.04 inches of mercury. Consultation of a carburetor icing probability chart published by the FAA showed that the possibility of serious icing at cruise power settings, and also fell within the range specified for icing in pressure-type carburetors. According to the kit manufacturer’s flight manual, takeoff procedure, “It is important to check full-throttle engine operations early in the take-off run. If there are any signs of rough engine operation or sluggish engine acceleration, discontinue the take-off. Investigate the cause of the poor engine operation before attempting another take-off.”