NTSB Identification: CHI94LA175.
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Accident occurred Wednesday, May 25, 1994 in TOULON, IL
Probable Cause Approval Date: 02/14/1995
Aircraft: HUGHES 269B, registration: N9375S
Injuries: 2 Minor.

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 HELICOPTER HAD BEEN REASSEMBLED AFTER AN ANNUAL INSPECTION, WITH INSTALLATION OF 3 OVERHAULED MAIN ROTOR BLADES. THE MAIN ROTOR BLADE DAMPERS HAD BEEN DISASSEMBLED, INSPECTED AND REASSEMBLED. DURING REASSEMBLY, THE INTERNAL SEQUENCE OF FRICTION DISCS WAS INCORRECT, RESULTING IN IMPROPER AND NON- UNIFORM DAMPING ACTION BETWEEN THE BLADES. THE SHOCK STRUT OLEOS WERE NOT SERVICED. POST ACCIDENT INSPECTION REVEALED LOW PRESSURE IN THE 3 REMAINING INTACT STRUTS. DURING THE FIRST TAKEOFF AFTER REASSEMBLY TO TRACK THE MAIN ROTOR BLADES IN A HOVER, THE HELICOPTER ENCOUNTERED GROUND RESONANCE AND WAS DESTROYED.

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

the improper reassembly of the main rotor blade dampers and the underservicing of the landing gear skid hydraulic struts which resulted in ground resonance of the helicopter when the first takeoff after reassembly was attempted.

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