NTSB Identification: CEN12LA353
14 CFR Part 91: General Aviation
Accident occurred Saturday, May 26, 2012 in Chesterfield, MO
Probable Cause Approval Date: 05/30/2013
Aircraft: SCHWEIZER 269C-1, registration: N345MH
Injuries: 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot reported that the helicopter started to shake as he increased power for takeoff on the solo instructional flight. He reduced engine power, but the oscillations became stronger and ultimately uncontrollable, resulting in substantial damage to the main and tail rotor blades, partial separation of the main rotor mast from the aft fuselage structure, and partial separation of the tail boom from the fuselage. The pilot shut down the engine and exited the helicopter. The pilot was receiving training for the addition of a helicopter rating and was operating the helicopter under the authority of a logbook solo endorsement. Postaccident testing revealed that all four landing gear dampers failed to meet the manufacturer’s specifications. The forward dampers were undercharged, while the aft dampers were overcharged. Maintenance records indicated that the aft dampers had been replaced with overhauled units about 1 month before the accident. The forward dampers had not been replaced. Maintenance procedures required periodic inspection of the landing gear dampers, and the operator stated that the inspection procedure was accomplished after installation of the overhauled dampers. A review of the overhaul procedure for the landing gear dampers revealed that the procedure did not provide for functional testing of the dampers following overhaul, which would have identified the out-of-specification condition before installation.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The undercharged and overcharged landing gear dampers, which allowed initiation of the ground resonance event from which the pilot was unable to recover due to his limited experience in helicopters. Contributing to the accident was the ineffective damper inspection conducted by the operator’s maintenance personnel and the improper overhaul procedure by the overhaul facility that resulted in overcharged dampers being provided to the operator. Also contributing was the lack of any final acceptance testing criteria for the dampers in the manufacturer’s overhaul procedure manual.

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