Diamond Aircraft Ind Inc DA 20-C1 N166SE accident near Beaver Falls, Pennsylvania

Probable cause

The operator’s maintenance personnel’s improper adjustment of the engine's fuel system, which resulted in a total loss of engine power.

NTSB analysis

According to the flight instructor, while on final approach, he perceived that the airplane was low on the desired glidepath. He said that he issued corrective instructions to the student twice before taking the flight controls. The instructor moved the throttle forward to increase power, and the engine stopped producing power. He selected a forced landing site, issued a Mayday call to the tower, and attempted an engine restart. However, he had to conduct a power-off landing on a roadway. Before ground contact, the airplane struck wires, and, during the accident sequence, the nose gear and tail section of the airplane separated.

During the examination of the wreckage, the engine was started, and it ran continuously on the airframe using the airplane's own fuel system. However, when the power was reduced to idle, the engine did not respond as expected to subsequent throttle and mixture inputs. After the initial run, the operator's director of maintenance was asked to produce the tools and documents used to calibrate the fuel system at installation. He produced instructions and gauges that resembled those used at the manufacturer’s factory, but no calibration stickers were displayed on the gauges. The gauges were installed, and, during a subsequent engine run, both the metered and unmetered fuel pressure readings were below factory specifications.

The fuel system was removed and flow tested at the engine manufacturer's facility. The fuel pump and fuel control assembly were intact, and bench testing demonstrated their ability to function, but both were found with several parameters outside of their respective calibrated specifications. The fuel manifold and nozzles were also tested and found to exhibit a normal flow vs. pressure indication on the test bench. The fuel pump was found adjusted "down" and flowed less than the required fuel flow specifications. The throttle body and mixture control unit were found adjusted to a position that allowed more than the required fuel flow at three specific settings. The combination of both the fuel pump and throttle body mixture control adjustments resulted in an idle fuel flow rate 2.5 times the maximum required. When the throttle was advanced quickly to full throttle, the fuel flow rate was 40 percent of the required rate. This significant transition in fuel flow rates likely resulted in a momentary "cavitation" of the fuel pump, which allowed air to enter the system and resulted in a total loss of engine power.

Text from the NTSB. Open the NTSB docket for ERA12LA246 for the full record.