Incident Summary
After completing air work, an instructor and student were returning to base. The instructor observed a loss of RPM from 2,300 to 1,100. He took over the aircraft controls from the student and attempted to correct the problem, but the RPM remained constant at 1,100. The instructor conducted the emergency checklist and informed the tower of the situation. He then landed the aircraft in an open field of high grass. During the landing, the nose wheel struck a hole, causing the aircraft to come to rest inverted.
Post-Accident Examination
An on-scene examination of the aircraft revealed that the bolt was in place, but the nut and cotter pin were missing from the carburetor throttle attachment assembly. It was also noted that the aircraft had flown approximately 15 hours since the last annual inspection and maintenance had been performed.