What happened
During a flight involving practice of agricultural turns at an altitude of a few hundred feet over fields, the crew was alternating control of the aircraft. While the rear seat occupant was performing a turn, the flight instructor abruptly added power, causing the engine to hesitate and cough. During this maneuver, the pilot experienced full aft elevator control input and reached the limit of the elevator control travel.
The passenger reported that while flying at approximately 150 feet above ground level at an airspeed of 60-70 mph, the left wing dropped. The aircraft subsequently impacted the ground. There were no fatalities reported in the accident.
The investigation
An FAA inspector examined the aircraft and found evidence that the left main landing gear made initial contact with the field, leaving a piece of landing gear tubing in the ground scar. The aircraft slid approximately 20 feet before coming to an upright rest. The impact caused the fuselage to break aft of the rear seat, displaced the empennage to the left, and moved the engine and cowling to the right. Impact damage was also noted on the left wingtip.
Mechanical examinations by the NTSB found no evidence of preimpact failure or malfunction regarding the flight controls for roll, pitch, or yaw. The ignition switch functioned satisfactorily, and the engine showed proper continuity in the crankshaft, camshaft, and valve train, with adequate suction and compression in all cylinders. Magnetos sparked correctly at all spark plugs during hand rotation.
Bench testing of the carburetor revealed that fuel leaked from the main metering nozzle when 6 psi of pressure was applied to the inlet. Disassembly of the carburetor showed a plastic needle valve was installed and a small amount of dirt was present in the throttle bowl area. The carburetor lacked an accelerator pump.