What happened
On June 12, 2021, a Diamond DA-40 NG operated by Motorfluggruppe Zürich departed from Zurich Airport (LSZH) at 10:42 AM. After departing via the "Sierra" waypoint and turning west, the aircraft's engine suffered an abrupt failure at an altitude of approximately 4,500 feet. The pilot initiated emergency procedures and performed an emergency landing in a field near Bünla, Bünzen (AG) at 10:55 AM. While the 0 fatalities and 0 injuries to the crew and passengers were a positive outcome, the aircraft remained intact, though a fuel leak was observed near the engine cowling after the occupants exited the plane.
The investigation
The investigation focused on the Austro Engine AE300 diesel engine and its common-rail injection system. Electronic control unit records revealed that fuel pressure within the system plummeted instantly from a normal operating pressure of approximately 1,600 bar to zero. Physical examination of the engine revealed that the threaded connection between the fuel pressure line and the injector for cylinder number 3 had become completely detached. This detachment caused the injector to shift, which subsequently damaged the injector plug and the fuel leak line.
Investigators also reviewed maintenance history, noting that the injector for cylinder number 3 had been removed, cleaned, and reinstalled with a new seal during a 300-hour inspection on March 24, 2021, roughly 32 flight hours prior to the incident. This maintenance was performed in Norway before the aircraft was imported to Switzerland.
Findings
- The engine failure was caused by a sudden loss of fuel pressure in the common-rail system.
- The loss of pressure occurred because the union nut connecting the fuel pressure line to the number 3 injector had loosened.
- The loosening of the connection was due to the nut not being properly tightened during the recent maintenance work performed in March 2021.