What happened
The pilot departed on a flight with a full load of water intended for calibrating the spray system. During a standard swath run, he heard a loud whirring noise and initially suspected a failure of the spray pump propeller. He immediately pulled up to initiate a left turn toward the runway while beginning to dump the water load. At this moment, he realized the aircraft had lost power and was unable to reach the runway.
Just prior to touchdown in a cut-over area, the left wing struck a stump, resulting in a crash. The engine separated from the airframe and came to rest partially submerged in a nearby drainage ditch.
The investigation
Examination of the wreckage revealed that the carburetor had separated from the engine assembly. The throttle control was found failed in tension. Crucially, the mixture control push-pull wire was not attached to the carburetor. An inspection of the attachment end of the mixture control wire showed no signs of tensile loading or scratches, and the hardware used to attach it could not be located.
Findings
The loss of power was directly caused by the mixture control wire detachment. Without this connection, the engine could not function properly, leading to the separation of the engine from the aircraft. The pilot's inability to maintain altitude resulted in the crash landing.