HOLLYWOOD, FL, USA
N81AM
HUGHES 269C
THE INSTRUCTOR PILOT WAS DEMONSTRATING COCKPIT AND RUNUP PROCEDURES TO THE STUDENT, WHEN THE HELICOPTER BECAME LIGHT ON THE SKIDS WITH OPERATING RPM & GROUND RESONANCE DEVELOPED. THE INSTRUCTOR BOTTOMED THE PITCH & SHUT OFF THE ENGINE, BUT THE GROUND RESONANCE BECAME WORSE. SUBSEQUENTLY, THE TAIL BOOM WAS CHOPPED OFF BY THE MAIN ROTOR BLADES, A FUEL CELL RUPTURED & A FIRE ERUPTED. ACCORDING TO AN FAA HANDBOOK (AC 61-13B), THE CORRECT PROCEDURE FOR GETTING OUT OF GROUND RESONANCE WAS TO LIFT OFF. AN EXAM REVEALED THE LEFT FRONT SHOCK STRUT WAS LOW.
THE SEVERE FUSELAGE VIBRATION (GROUND RESONANCE) AND THE PILOT'S IMPROPER PLANNING/DECISION TO AVOID OR COMPENSATE FOR THE OCCURRENCE. A FACTOR RELATED TO THE ACCIDENT WAS THE LOW SHOCK STRUT.
Source: NTSB Aviation Accident Database
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