What happened
On 26 October 2009, a Thruster T600N 450, registration G-EVEY, was conducting a training flight near Newtownards Airfield in Northern Ireland. While the aircraft was at a circuit height of approximately 700 ft, the student pilot turned downwind and began reducing engine power to cruise settings. During this maneuver, a rumbling sound originated from the front of the engine. Roughly ten seconds after the noise was heard, the propeller became detached from the engine.
The instructor in command took control of the aircraft and performed a forced landing in a field, a location frequently utilized for practicing engine failure procedures. The landing was successful, and there were no injuries to the two crew members on board. Aside from the loss of the propeller, the aircraft sustained no further damage.
The investigation
Following the incident, an examination of the aircraft components was conducted. Investigators focused on the propeller mounting assembly to determine why the component had separated from the engine. The inspection of the propeller attachment bolts revealed significant evidence of extensive fatigue crack propagation. The investigation established that these cracks progressed until the bolts reached a point of ductile overload, which ultimately caused the propeller to detach from the engine.