What happened
During a winching operation located in a re-entrant near a waterfall, the pilot positioned the helicopter to allow for a descent to a lower hover height. This positioning was intended to provide an escape route and mitigate the risk of a conical spin, but it placed a nearby tree in the pilot's blind spot. While the aircrew officer (ACO) and paramedic were performing pre-winch checks, the pilot was left with sole responsibility for monitoring obstacles.
As the crew prepared for the winch, the aircraft began to drift toward the tree. The doctor on board noticed the drift toward the rear-left obstacle, but the ACO did not resume providing external clearances because the paramedic had not yet descended below the airframe. Once the winching process began, the doctor alerted the crew to the drift, prompting a command to move right. In attempting to correct the position with a right roll and increased collective, the main rotors struck the tree.
The investigation
The investigation examined the positioning of the aircraft and the division of responsibilities among the crew. It was found that the proximity of surrounding trees caused recirculation, which disturbed the stable hover and increased the control inputs required by the pilot. The investigation also looked into the transition of clearance duties between the ACO and the pilot during the pre-winch briefing phase.
Findings
- The crew positioned the aircraft such that the nearest obstacle was located within the pilot's blind spot.
- The pilot assumed sole responsibility for obstacle clearances to allow the ACO and paramedic to conduct safety briefs.
- The aircraft experienced drift due to the effects of recirculation from nearby trees.
- The pilot failed to detect and correct the drift toward the obstacle while the ACO was not providing clearances.
- The pilot's attention may have been diverted by the briefings, or they may have incorrectly assumed the ACO had resumed scanning.