Amateur-built ROTORWAY EXEC N48KM accident near Iron Station, North Carolina

Probable cause

The pilot’s failure to maintain adequate clearance from the ground while hovering, which resulted in separation of the forward section of the right skid tube with counterweight attached, a sudden center of gravity (CG) shift outside the normal operating range, and a subsequent loss of control.

NTSB analysis

The private pilot said that, while in a hover during the fifth of a series of test flights, the experimental amateur-built helicopter pitched up and to the left and began transitioning rearward. He corrected with a full, right-forward cyclic input, yet the helicopter continued to transition to its rear until it struck a hangar. The helicopter continued inside the open hangar, collided with an airplane, and came to rest on its left side. The helicopter sustained substantial damage to the cockpit, fuselage, and tail boom. The pilot reported the helicopter had performed "flawlessly" prior to the loss of control.

Before the test flights, the helicopter was configured with a ballast weight located on the right skid as prescribed in the pilot operating handbook for solo operation. Following the accident, the forward section of the right main landing gear tube, with the counterweight ballast attached, was found between where the helicopter hovered for the test, and where it came to rest inside the hangar. The tube's fracture surface features were consistent with overstress, and no indications of preexisting cracking or corrosion were observed. Given the location of the separated skid tube after the accident, it is likely that the skid contacted the ground while hovering, which resulted in an overstress separation of the skid tube and attached counterweight. This subsequently resulted in a sudden center of gravity (CG) shift outside the normal operating CG range and a loss of control.

Text from the NTSB. Open the NTSB docket for ERA16LA301 for the full record.