BFO93LA112

The pilot reported that the engine began to 'run rough' about 20 minutes after departure during cruise flight at 5,500 feet. He stated that he applied carburetor heat, but the engine 'quit completely'. A forced landing was executed. The airplane landed on rough terrain and nosed over. An FAA aviation safety inspector examined the airplane and stated that 'carburetor icing is suspected'. The engine was successfully run after the accident.

On July 6, 1993, about 1515 hours eastern daylight time, N7954U, a Cessna 172, owned by Richard A. Wilkinson and Larry W. Brubaker of Curwensville, Pennsylvania, sustained substantial damage during a forced landing in a field near Normalville, Pennsylvania. The pilot and two passenger received minor injuries. Visual meteorological conditions prevailed and a flight plan was not filed. The cross country flight departed Morgantown, West Virginia, at about 1450 hours and was destined for Clearfield, Pennsylvania. The personal flight was conducted under 14 CFR Part 91.

According to the pilot, the airplane had just been purchased by the two passengers and was being ferried to the Clearfield Lawrence Airport in Clearfield, Pennsylvania. The pilot stated, "After departure at 5500 feet the mixture was leaned. Within a few minutes, the engine began to run rough. The mixture was selected rich, carburetor heat was applied, [and the magnetos] were checked. Checked fuel selector valve to [left tank] through BOTH to [right] tank and back to BOTH. Engine quit completely. Emergency landing area was selected. Turned final to selected area on [a heading of about 250 degrees]. Landed [about] 150 feet of selected field. . . . "

According to a Federal Aviation Administration (FAA) aviation safety inspector, post accident examination of the airplane and accident site revealed the airplane contacted the ground, slid 45 feet, and then nosed over. According to the inspector, "The aircraft was righted, a continuity inspection of the engine and fuel system was satisfactory, inspection of several spark plugs revealed a dark brown color that was not supported by the exhaust, carburetor ice is suspected. Installed spark plugs, cleared exhaust and intake, started engine, limited to 1000 [revolutions per minute] because of bent propeller, magnetos checked satisfactory."

The reported surface temperature and dewpoint at a weather observation facility located about 50 statute miles from the accident site were 90 degrees F and 66 degrees F respectively. According to the pilot, the airplane was at 5,500 feet when the engine roughness occurred. According to "DOT/FAA/CT82/44 Publication; Light Aircraft Piston Engine Carburetor Ice Detector/Warning Device Sensitivity/Effectiveness" the probability of "[carburetor] icing at glide power and cruise power" exists in the aforementioned temperature/dewpoint conditions.

According to the Cessna Aircraft Company Model 172 Information manual, Section 3, "A gradual loss of RPM and eventual engine roughness may result form the formation of carburetor ice. To clear the ice, apply full throttle and pull the carburetor heat knob full out until the engine runs smoothly; then remove carburetor heat and readjust the throttle."