Incident Overview
A helicopter pilot was conducting an aerial survey of a drop zone for an external load operation. The pilot determined that there was sufficient room to belly hook the load instead of using a long line. As the helicopter descended to the drop zone, the main rotor blades struck pine trees measuring 1 to 2 inches in diameter. The pilot was unaware of the collision at the time.
Sequence of Events
After the impact, the pilot continued with the load drop. Following the release of the external load, the pilot initiated a vertical climb to clear the surrounding trees, then transitioned to forward flight. At approximately 40 knots, the pilot felt a vibration and decided to fly the helicopter back to the cargo loading site, a distance of 3.5 miles.
Post-Flight Inspection
Upon landing, the main rotor blades were inspected and evidence of the collision was noted on both blades. The ground crew member stationed at the drop zone, who was in communication with the pilot, reported that she was "awestruck" when the collision occurred. She allowed the drop to continue and did not notify the pilot of the collision at the time.
Findings
The event involved a helicopter conducting an external load operation. The main rotor blades struck trees during descent. The pilot was unaware of the strike until after the flight.