Incident
Witnesses reported that the airplane was in a wide spiral, then it suddenly entered a dive and crashed. One witness, who was outside and away from structures, reported that the engine was sputtering just before impact.
Pilot Accounts
The dual student retained only a fragmented memory of the day of the accident. However, he remembered that the instructor took control of the airplane when the engine began to sputter during a power application. Additionally, the student reported that carburetor heat had been used prior to the application of power.
Training History
A review of the instructor and student logbooks showed that instruction in emergency procedures had been conducted during the previous period of instruction.
Investigation
No preimpact part failure was found during the investigation. The engine was mounted on a test stand and operated to 1000 revolutions per minute (RPM). The temperature and dew point were reported to be 54 degrees and 47 degrees, respectively. According to icing probability charts, conditions were conducive to serious icing at cruise power.