Diamond DA20 N346MA accident near Mccormick, South Carolina

Probable cause

A partial loss of engine power due to debris obstructing the metering plug orifice in the throttle and metering unit.

NTSB analysis

After the accident airplane experienced a partial loss of engine power the previous day, the accident pilot/mechanic was dispatched to perform maintenance on the airplane. The previous pilot reported that after landing, the engine would not run with the electric fuel pump turned off. The engine would run slightly better if the primer was on.

The accident pilot/mechanic replaced the throttle and metering unit, the engine-driven fuel pump, and the manifold valve with overhauled units. He set the metered and unmetered fuel pressures to within specifications and the engine ran satisfactorily. A preflight inspection revealed no anomalies, and the pilot departed. After takeoff, the pilot initially remained in the traffic pattern until he was satisfied that the engine was performing normally. He then began to climb and proceeded toward his destination when the engine lost partial power and would not respond to throttle inputs. The pilot performed a forced landing to a nearby clearing, during which the airplane impacted trees, resulting in substantial damage to the fuselage and left wing.

A test run of the engine at the manufacturer’s facility found that it ran very rough and would not idle. Similar to the conditions reported by the previous pilot, the engine would remain running only when the test stand fuel boost pressure was increased beyond the normal values.

Examination of the throttle and metering unit revealed debris lodged in the metering plug orifice, obstructing about 90% of the opening. When the debris was removed, the engine ran normally and within manufacturer specifications. Examination of the debris found that it was similar in composition to a sample of torque putty, commonly used to mark threaded fittings after assembly; however, there was no indication that torque putty was used on any of the as-installed fuel system components or on the components that were removed before the accident. Similar debris was found in the previously installed manifold valve (the one removed prior to the accident flight) downstream of the internal filter screen.

The origin of the debris or when it may have been introduced into the fuel system could not be determined. The debris was too large to pass through the fuel pump inlet screen or the airframe filter bowl, making it unlikely to have been introduced during fueling.

Given that debris was found in two different components, one installed on the day of the accident and the other removed before the flight (and found downstream of filters), it was likely introduced during one or more maintenance events. However, it could not be determined if it occurred during the maintenance performed on the day of the accident, a previous maintenance event, or both.

Text from the NTSB. Open the NTSB docket for ERA19LA074 for the full record.