What happened
On December 19, 2018, a Diamond DA20, registration N346MA, was involved in an accident in McCormick, South Carolina, during a post-maintenance test flight. The aircraft was being operated under 14 CFR Part 91.
The day prior to the accident, a different pilot had performed a precautionary landing at McCormick County Airport (S19) due to a partial loss of engine power. That pilot noted the engine would not run if the electric fuel pump was turned off and performed better if the primer was active.
The pilot of the accident flight, who was also a mechanic, traveled to S19 to diagnose the issue. After finding the engine was not running smoothly, he replaced the throttle and metering unit, the engine-driven fuel pump, and the fuel manifold valve. Following these replacements, he adjusted the fuel pressures to within limits and verified the engine ran satisfactorily at idle, during run-up, and at full power. After a preflight inspection and fuel sump check, the pilot departed from runway 36.
After initially remaining in the traffic pattern, the pilot began a climb toward Newnan Coweta County Airport (CCO) in Georgia. At an altitude between 3,000 and 3,500 feet, the engine suffered a partial loss of power. The engine speed dropped from approximately 2,500 rpm to 1,000 rpm and failed to respond to throttle inputs. Despite attempts to adjust the mixture and fuel boost pump, the pilot was unable to restore power. He attempted an emergency landing in a clearing approximately one mile southwest of the airport, where the aircraft struck trees. The accident resulted in 2 minor injuries and no fatalities.
The investigation
An FAA inspector examined the wreckage and found the left wing had separated from the fuselage at the root, and a large portion of the canopy and roof was fragmented.
The engine was examined at the manufacturer's facility, where it was found to run roughly and would not idle unless the test stand fuel boost pressure was increased beyond normal values. Testing of the throttle and metering unit revealed that a small piece of green, glassy debris, approximately 1/16 of an inch square, was obstructing about 90% of the metering plug orifice area. This debris was too large to have passed through the fuel pump inlet screen or the airframe fuel filter bowl.
Further examination of the fuel manifold valve removed prior to the accident flight revealed similar debris on the downstream side of the manifold's filter screen. Laboratory analysis identified the debris as being similar in composition to "torque putty," a substance used to mark threaded fittings after assembly. While the debris was found in both the newly installed and the previously removed components, investigators could not determine exactly when the material was introduced into the fuel system.