Incident
According to the flight instructor, the aircraft was in cruise flight when a sudden severe vibration propagated through the airframe. In response, the pilot shut down the engine. Post-shutdown inspection revealed that the brass abrasion strip and a portion of one wooden propeller blade had separated from the assembly.
Landing
The pilot executed an emergency landing in a field. However, the aircraft could not be brought to a stop before it traveled down an embankment and into a ravine.
Recovery
An airframe and powerplant mechanic who recovered the aircraft reported observing evidence of dry rot in the remaining wooden blade section. No other conditions or causes were identified during recovery.