What happened
The pilot was conducting aerial spray operations over a wooded area when the low RPM warning activated. At this point, the pilot observed the rotor and engine RPM readings decreasing rapidly. In response to the mechanical issue, the pilot initiated an autorotation descent to control the aircraft's altitude.
During the landing phase of the maneuver, the aircraft struck trees before impacting the ground. The helicopter came to rest on its left side following the collision with the terrain and vegetation.
The investigation
A post-accident examination of the aircraft was conducted to determine the cause of the RPM loss. The inspection did not disclose evidence of a mechanical malfunction or pre-impact failure within the airframe or powerplant systems that would account for the sudden drop in RPM readings.
Findings
The primary factor leading to the accident was the rapid decrease in rotor and engine RPM during flight operations. This mechanical anomaly necessitated an emergency autorotation, which ultimately resulted in the aircraft striking trees and crashing. The investigation confirmed the absence of detectable mechanical defects prior to the impact.