Accident Sequence
On June 4, 2013, at about 1700 central daylight time, a Stinson 108, registration N97592, was substantially damaged during a forced landing shortly after takeoff from Standard Field (5KY4) in Elkton, Kentucky. The commercial pilot and one passenger incurred minor injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight destined for Russellville-Logan County Airport (4M7) in Russellville, Kentucky. Visual meteorological conditions prevailed, and no flight plan was filed.
The pilot stated that the purpose of the flight was to practice takeoffs and landings on the turf runway at 5KY4. After an uneventful departure from 4M7 and a full-stop landing at 5KY4, the pilot taxied back, took off from runway 31, and entered the airport traffic pattern. During the next landing, the airplane touched down about one-third down the runway. Intending to perform a touch-and-go landing, the pilot increased engine power to full, and the airplane began to climb.
During the climb, the pilot reported that the engine sounded normal and smooth, but the climb rate seemed slower than previously observed. With about one-third of the runway remaining, the pilot confirmed the throttle position and flap setting. Upon reaching the end of the runway, the pilot realized that "something was wrong." Believing the airplane might clear a line of trees located about 1,500 feet beyond the departure end, he attempted to increase the climb rate by increasing the pitch angle. At an altitude of about 60 to 80 feet, realizing the airplane would not clear the trees, the pilot turned left toward a field and decreased the pitch angle. The airplane descended, and the pilot attempted to land in the soft ground of a corn field. During the landing roll, the airplane nosed over, resulting in substantial damage to the airframe.
Pilot and Aircraft Information
The pilot held a commercial pilot certificate with ratings for airplane single-engine and multi-engine land, and instrument airplane. His most recent FAA third-class medical certificate was issued in April 2011. He reported 1,033 total hours of flight experience, of which 3 hours were in the accident airplane make and model.
Standard Field consisted of a single turf runway 2,930 feet long by 75 feet wide at an elevation of 665 feet.
Weather Conditions
Weather conditions reported at Outlaw Field (CKV) in Clarksville, Tennessee, about 16 nautical miles southwest of the accident site, at 1653 included calm winds, 10 statute miles visibility, clear skies below 12,000 feet, temperature 27°C, dew point 13°C, and an altimeter setting of 29.99 inches of mercury. According to a Federal Aviation Administration (FAA) carburetor icing probability chart, these temperature and dew point conditions were conducive to the formation of serious carburetor icing at glide engine power settings.
Wreckage Examination
An FAA inspector examined the wreckage. The engine remained intact with no breaches of the engine case. Continuity of the valvetrain was confirmed through limited rotation of the propeller. Four spark plugs exhibited normal wear with some residual carbon buildup. The gascolator-to-carburetor fuel hose contained fuel free of contamination, and the carburetor fuel screen was absent of debris. All carburetor controls remained attached and functional. The carburetor heat control was found in the "off" position and functioned normally when actuated. No evidence of any pre-impact mechanical malfunctions or failures of the engine was noted.
The airframe examination revealed that primary and secondary flight controls operated normally, and both wing fuel tanks contained adequate fuel.
Pilot's Statements
When speculating about the partial loss of power during the climb, the pilot stated that the engine sounded normal throughout and did not exhibit a loss of rpm. He also stated that during the approach to landing that immediately preceded the accident takeoff, he did not recall utilizing the carburetor heat, and that carburetor icing was one possible explanation for the loss of power.
According to the manufacturer's published operating limitations, during landing, the carburetor heat control should be placed fully on if possible icing conditions exist. The published takeoff distance and climb to an altitude of 50 feet for the airplane, assuming maximum gross weight, flaps retracted, and a hard-surface runway, was about 1,800 feet under the reported weather conditions.
The FAA Pilot's Handbook of Aeronautical Knowledge describes that carburetor ice forms due to fuel vaporization and decreased air pressure in the carburetor's venturi, causing a sharp temperature drop. If water vapor condenses at or below freezing, ice may form on internal carburetor surfaces, including the throttle valve, restricting the fuel/air mixture and reducing engine power. The first indication of carburetor ice in an airplane with a fixed-pitch propeller is typically a decrease in engine rpm, possibly followed by engine roughness. Carburetor heat is an anti-icing system that preheats air before it reaches the carburetor to prevent ice formation; it can also melt existing ice if the accumulation is not too great.