The instructor and student were conducting a night orientation flight. According to a witness who worked for the operator, about 15 minutes after the helicopter departed, he heard what sounded like an engine rollback and the helicopter making an autorotation. This was followed by the sound of an increase in engine rpm and the drive belts squealing, culminating with the sound of the helicopter making a loud thud-type noise. Another witness stated that the engine sounded rough and that the helicopter was making a high pitch whining/squealing sound, after which it went silent. A third witness also heard the helicopter making a high-pitch noise just before the accident. The helicopter was subsequently located in an open field near the departure airport; a post-crash fire erupted, which consumed the helicopter.