What happened
During a qualification training session for the new owner of the aircraft, the pilot was performing a series of stop-and-go landings. During the fifth attempt, the pilot retarded the throttle to idle while abeam the intended landing point. As the aircraft proceeded on the base leg, the pilot attempted to advance the throttle to adjust the rate of descent, but the engine failed to respond and remained at idle speed.
The controls were transferred to the instructor, who also attempted to increase power but was unsuccessful. The crew subsequently performed a forced landing into a cultivated field. During the impact with the furrows in the field, the left main gear was severed.
The investigation
An examination of the wreckage identified that a retaining clip used to anchor the throttle cable assembly to the firewall was missing. This absence allowed the entire housing to move whenever the throttle was advanced or retarded, preventing the engine from responding to pilot inputs.