Incident
A flight instructor experienced a loss of engine power during a training flight. The instructor activated the carburetor heat and advanced the throttle to full power. After 30 seconds with no improvement in engine performance, the instructor decided to execute a forced landing into a field. During the landing on soft terrain, the nose gear collapsed, and the airplane came to rest on its nose.
Instructor Report
The instructor reported no mechanical malfunctions with the airframe or engine. She suspected that carburetor ice caused the power loss.
Weather Conditions
The instructor noted a broken layer of clouds at 2,800 feet MSL. At 2,000 feet MSL, the temperature was 60°F with a relative humidity between 55 and 59 percent. The closest weather reporting station recorded a surface temperature of 66°F and a dew point of 41°F. According to a carburetor icing probability chart, these conditions were conducive for moderate icing at cruise power and serious icing at descent power.