Iron Station, NC, USA
N48KM
MEANS ROBER C ROTORWAY EXEC
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.
On August 26, 2016, about 1450 eastern daylight time, an experimental amateur-built Rotorway Exec, N48KM, was substantially damaged following a loss of control while in hovering flight at Lincolnton-Lincoln County Regional Airport (IPJ), Iron Station, North Carolina. The private pilot sustained minor injuries. Visual meteorological conditions prevailed and no flight plan was filed for the local maintenance test flight which was conducted under the provisions of Title 14 Code of Federal Regulations Part 91.According to the pilot, the purpose of the flight was to confirm the dynamic track and balance condition of the main rotor system following the replacement of elastomeric bearings in the main rotor hub. Four ground and hover tests had been performed previous to the accident flight. In an interview with a Federal Aviation Administration (FAA) aviation safety inspector, the pilot said that while at a hover, the helicopter pitched up, 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 tailboom. Prior to the flights, the helicopter was configured with a ballast weight located on the right skid as prescribed in the pilot operating handbook (POH) for solo operation. Following the accident, the forward section of the right main landing gear tube, with counterweight ballast attached, was found between the positions of the helicopter where it hovered for the test, and where it came to rest. Examination of the helicopter by FAA inspectors confirmed cyclic and collective control continuity. Additionally, the pilot reported that the helicopter had operated "flawlessly" up until the time of the accident. The helicopter's most recent condition inspection was completed on July 22, 2016, at 254 total aircraft hours. The pilot held a private pilot certificate with ratings for airplane single engine land and rotorcraft-helicopter. His most recent Federal Aviation Administration (FAA) third-class medical certificate was issued on March 14, 2016. He reported 600 total hours of flight experience, of which 500 were in the accident helicopter make and model. Weather reported at the time of the accident included winds from 080 degrees at 4 knots, 10 statute miles visibility, clear skies, temperature 34 degrees C, dew point 17 degrees C, and an altimeter setting of 30.11 inches of mercury. The forward section of the right main landing gear tube was forwarded to the NTSB Materials Laboratory in Washington, DC for examination. According to the Material Engineer's report, "The features on the fracture surface of the separated end were consistent with overstress. No indications of preexisting cracking or corrosion were observed."
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.
Source: NTSB Aviation Accident Database
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