Accident Summary
On December 19, 2018, about 1420 eastern standard time, a Diamond DA20, registration N346MA, was substantially damaged during an accident in McCormick, South Carolina. The pilot and passenger sustained minor injuries. The airplane was operating under 14 CFR Part 91 as a post-maintenance test flight.
Preceding Events
The day before, another pilot made a precautionary landing at McCormick County Airport (S19) due to a partial loss of engine power. After landing, the engine would not run with the electric fuel pump off, and ran slightly better with the primer active (which operates the electric fuel pump on HIGH).
Maintenance and Repairs
The accident pilot, holding a mechanic certificate, was dispatched to S19 to diagnose and repair the airplane. After starting the engine, which ran roughly, he tested the fuel-injected engine and found unmetered fuel pressure above limits at 1,000 rpm and metered fuel pressure below limits at full power. He replaced the throttle and metering unit (fuel control unit), engine-driven fuel pump, and fuel manifold valve (flow divider/distribution manifold). After replacing the manifold valve, he adjusted both pressures within limits, and the engine ran satisfactorily at idle, run-up, and full power. A coworker verified the work with no fuel leaks. Before takeoff, the pilot performed a preflight inspection, sumped fuel drains three times finding no debris, and checked fuel quantity (about 3/4 full). He ran a normal run-up, departed from runway 36, stayed in the traffic pattern, then climbed toward Newnan Coweta County Airport (CCO).
Partial Power Loss and Emergency Landing
At 3,000–3,500 feet, the engine lost partial power, dropping from 2,500 rpm to 1,000 rpm and not responding to throttle. The pilot verified rich mixture and boost pump on, attempted throttle adjustments, but power was not restored. He turned back toward S19, prepared for an emergency landing, but realized he could not reach the runway. He attempted to land in a clearing about 1 mile southwest of the airport, during which the airplane impacted trees.
Wreckage and Engine Examination
An FAA inspector noted the left wing separated at the root, and a large section of roof and canopy was fragmented. The engine was examined at the manufacturer's facility under NTSB oversight. On a test stand, it ran rough and would not idle unless boost pressure was increased. The throttle and metering unit was removed and tested; fuel flow was below acceptable range at all throttle positions. Disassembly revealed a piece of green glassy solid debris about 1/16" square obstructing about 90% of the metering plug orifice. The debris was too large to pass through the fuel pump inlet screen or gascolator. After debris removal and reinstalling the unit, engine runs appeared normal.
Fuel Manifold and Debris Analysis
The removed fuel manifold valve contained several pieces of debris on the downstream side of its filter screen. The debris appeared identical in color to that found in the throttle unit but were smaller, yet still too large to pass through the manifold screen. The debris was sent to the NTSB materials lab. Fourier transform infrared spectrometer examination showed its composition was similar to, but not an exact match of, an exemplar sample of "torque putty." Torque putty is used to mark threaded fittings after torquing; during disassembly, it is typically removed. At engine examination, none of the fuel system fittings were marked with torque putty.
Fuel System Configuration
Fuel flows from a single tank through two outlet finger screens to a filter bowl, then the electrical fuel pump, a shutoff valve, the engine-driven fuel pump (with inlet finger screen), the throttle and metering unit, the manifold valve (with internal filter screen), and then via four lines to cylinders through injector nozzles.
Maintenance Records
Records from the 13 months preceding the accident showed only three fuel system entries: on 8/17/18 (set fuel flow injection pressure, 549 flight hours prior), 8/29/18 (replaced inoperative boost pump and set fuel flow, 426 hours prior), and 8/30/18 (set fuel flow injection pressure, 422 hours prior).