RIALTO, CA, USA
N7441F
HUGHES 269C
THE HELICOPTER ENCOUNTERED GROUND RESONANCE DURING A MAINTENANCE TEST FLIGHT. THE CFI NOTICED AN UNUSUAL VIBRATION DURING STUDENT TRAINING. THE PILOT SUSPENDED THE TRAINING AND INFORMED MAINTENANCE. THE PILOT THEN ATTEMPTED TO DUPLICATE THE VIBRATION FOR ONE OF THE MAINTENANCE MECHANICS. AFTER TWO UNSUCCESSFUL ATTEMPTS, THE PILOT LANDED THE HELICOPTER ON A SLIGHT SLOPE. AFTER ONE SKID TOUCHED DOWN, THE HELICOPTER BEGAN TO VIBRATE. THE PILOT REDUCED THE THROTTLE AND THE VIBRATION BECAME MORE SEVERE. ACCORDING TO THE PILOT, THE HELICOPTER BEGAN TO DISINTEGRATE.
IMPROPER MAINTENANCE PROCEDURE BY MAINTENANCE PERSONNEL TO TROUBLESHOOT A REPORTED DEFICIENCY AND THE PILOT'S DECISION TO DEMONSTRATE THE VIBRATION, EXCEEDING THE DESIGN LIMITS OF THE HELICOPTER AND INDUCING GROUND RESONANCE. CONTRIBUTING TO THE ACCIDENT WAS THE LOW NITROGEN CHARGE OF THE LANDING GEAR DAMPERS.
Source: NTSB Aviation Accident Database
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