What happened
On June 22, 2017, a Diamond DA-40 D aircraft, registration PH-EMW, was conducting a private flight from Eindhoven Airport when the pilot experienced significant engine power fluctuations. During the cruise phase, the pilot noticed engine vibrations and inconsistent power settings. As the aircraft attempted to climb to 1,500 feet, the available power dropped sharply to approximately 60%, preventing the aircraft from maintaining its altitude.
Unable to sustain the climb, the pilot initiated an emergency landing in a field near Haaren. While the landing was initially gentle, the aircraft struck the bank of a ditch. The impact resulted in substantial damage to the aircraft, including broken landing gear and broken propeller blades. Both the pilot and the passenger escaped the incident without injuries.
The investigation
The Dutch Safety Board (OVV) examined the engine and the Full Authority Digital Engine Control (FADEC) system. The investigation involved analyzing the engine components at the manufacturer's facilities in Germany and Austria. Investigators focused on the electrical connection between the engine wiring harness (loom) and the FADEC unit.
Testing on a test bench revealed that manually moving the FADEC connectors caused the engine RPM to fluctuate and triggered failure warnings. Microscopic analysis of the connectors showed tool marks on the union nuts, indicating that a wrench had been used to force the connection. Furthermore, investigators discovered that the internal surfaces of the connectors were damaged and that the pins had been misaligned.
Findings
- The power fluctuations were most likely caused by damaged engine loom connectors, which created intermittent electrical contacts between the engine and the FADEC.
- The damage originated from a maintenance error where the FADEC was installed upside down because the support brackets were fitted without following the official Repair Manual.
- Because the FADEC was inverted, the mechanic attempted to connect the wrong loom connectors to the sockets and used a wrench to force them into place, despite the connectors being designed for hand-tightening only.
- This improper installation caused a cross-connection of the pins and physical damage to the connector internals, which went unnoticed during the subsequent installation of a replacement FADEC unit.