Event Description
While en route to the practice area, a student pilot executed several practice turns. During these maneuvers, she observed a loss of altitude. In response, she added throttle to regain altitude but did not receive a corresponding power indication. She checked the fuel selector to confirm it was in the on position and then examined the engine gages, which showed no discrepancies. Carburetor heat was applied with no response, and the engine rpm continued to drop. She crosschecked the engine instruments and reapplied carburetor heat without any change. As the rpm continued to decrease, she performed an emergency landing in a plowed dirt field.
Engine Inspection
Following the landing, the engine was inspected. It was noted that the retaining nut attaching the serrated throttle lever to the serrated throttle shaft of the carburetor was loose, and the cotter pin was missing. The serrated portion of the throttle lever was unable to properly engage with the serrated stop of the throttle shaft. The carburetor had been replaced during the annual inspection on June 6, 1999, to comply with Airworthiness Directives. No further discrepancies were noted.
Findings
The loose retaining nut and missing cotter pin prevented the throttle lever from properly engaging with the throttle shaft, which likely resulted in the loss of power control during the flight.