Robinson Helicopter Company R44 II N4361R accident near Durkee, Oregon

Probable cause

The pilot's inadequate performance planning, which resulted in insufficient engine power to transition into an out-of-ground-effect hover at a high gross weight.

NTSB analysis

The pilot of the helicopter was using a 50-ft long line to transport equipment to a camp site. He estimated the gross weight of the helicopter to be about 2,450 lbs, the elevation to be about 5,300 ft mean sea level (msl), and the temperature to be about -1°C, for a density altitude of about 4,500 ft. After picking up the load from a staging area and conducting multiple power checks, he determined the conditions were acceptable. While transitioning to a hover out-of-ground-effect (OGE), about 60 ft above ground level (agl), the engine and rotor speed began to decay, and the helicopter lost lift and began descending. The pilot released the load and entered an autorotation. During the landing on sloping terrain, the main rotor blades impacted a tree, the right skid contacted the ground, and the helicopter rolled onto its side, which substantially damaged the fuselage, empennage, and tail cone.

Examination of the helicopter revealed no preaccident mechanical malfunctions or failures that would have precluded normal operation. Examination of the main rotor blades revealed excessive upward coning, consistent with low rotor speed and the whooshing sound reported by the pilot. A test run of the engine revealed no anomalies. The individual who loaded the equipment stated that they normally weighed the loads; however, they did not do so on this occasion.

Performance calculations revealed that, given the environmental conditions at the accident site around the accident time, the helicopter would have been marginally capable of an OGE hover at 2,450 lbs. The pilot conducted multiple power checks and assessed the conditions as acceptable; however, once the pilot transitioned the helicopter to an OGE hover with the external load, the power required to hover OGE likely exceeded the available engine power. Given the fact that the engine test run revealed no anomalies, the density altitude, the weight of the cargo, or both were likely higher than the pilot estimated, which would have reduced the helicopter’s OGE hover performance.

Text from the NTSB. Open the NTSB docket for WPR25LA034 for the full record.