What happened
Prior to departure, the pilot performed a pre-flight inspection of the Cessna 172 in an unheated hangar. Although temperatures were below freezing, the engine had been warmed using a pre-heater and an engine blanket. During the inspection, no ice crystals were observed in the fuel sample. After startup, the aircraft remained on the ground for a period of time while the pilot applied carburetor heat for at least 10 minutes. Just before takeoff, the pilot noted the carburetor temperature was 20 degrees C and subsequently secured the carburetor heat.
During the takeoff roll on the 1,800-foot turf runway, the engine failed to reach full power, though it continued to operate smoothly. The pilot observed less-than-normal manifold pressure and noted that the aircraft did not require the usual right rudder inputs to maintain directional control. Approximately two-thirds of the way down the runway, which was frozen and rutted but without snow cover, the pilot became concerned regarding the engine power. Believing that stopping was unrealistic and that the aircraft could clear a hedgerow at the end of the runway, the pilot continued the takeoff attempt. The aircraft failed to clear the hedgerow.
The investigation
Federal Aviation Administration inspectors examined the aircraft following the accident and found no mechanical anomalies. Additionally, the carburetor was removed and inspected at an engine overhaul facility, where the mechanic found no conditions that would have prevented proper functioning. Analysis of ambient temperature and dew point readings from three nearby airports indicated no probability of icing. At the time of the accident, the interpolated temperature and dew point at the nearest airport were 6 degrees Fahrenheit and 0 degrees Fahrenheit, respectively.