What happened
While attempting to pick up a 100-foot sling load of seismic equipment, the pilot of an Aerospatle AS 350 BA positioned the aircraft in a high hover near a staging area. During this maneuver, the pilot experienced a physical vibration in the cyclic controls and heard the low rotor RPM warning horn. In response, the pilot increased engine power to move the aircraft away from the site. The helicopter subsequently moved toward a nearby creek bed, where it performed a hard landing on a sand bar. The pilot escaped the incident without injury, though the aircraft suffered substantial damage.
The investigation
Investigators determined that the main rotor blades had made contact with a tree located behind the helicopter, which was positioned outside the pilot's field of vision. This impact caused one blade to lose structural integrity, resulting in the loss of blade material from the tip toward the mid-section.
An examination of the engine revealed damage consistent with the sequence of events following the blade strike, specifically noting high operating temperatures caused by the pilot's control inputs after the impact. The investigation also confirmed that the engine was producing sufficient power at the time of the strike, as the pilot was able to maneuver away from the staging area, and the low rotor horn activation was linked to the momentary drop in RPM caused by the tree strike rather than an engine failure. Additionally, the inspection found that the airframe damage was a direct result of the hard landing on the sand bar.
Findings
- The primary cause of the incident was that the main rotor blades struck a tree.
- The tree was situated behind the aircraft and remained out of the pilot's line of sight during the hover.
- The pilot was operating the helicopter in an area where the rotor blades could come into contact with trees located behind the aircraft.