NTSB Identification: LAX88FA249.
The docket is stored on NTSB microfiche number 40438.
Accident occurred Friday, July 08, 1988 in VAN NUYS, CA
Probable Cause Approval Date: 06/25/1990
Aircraft: HUGHES 269C, registration: N750AM
Injuries: 2 Minor,1 Uninjured.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

THE PLT LIFTED OFF TO A HOVER DURING A PASSENGER CARRYING SIGHT-SEEING FLIGHT. UPON FEELING A VIBRATION THE PLT LANDED AND TOUCHED DOWN SOFTLY. AS THE MAIN ROTOR BLADES SLOWED THE VIBRATION INTENSIFIED, AND AIRFRAME DESTRUCTION BY GROUND RESONANCE RESULTED. THE PREVIOUS DAY THE COMPANY'S CONTRACT MECHANIC COMPLETED A 100-HR INSPECTION. THE MECHANIC WAS RESPONSIBLE FOR ENSURING THE BLADE DAMPER'S TORQUE WAS SET IN COMPLIANCE WITH MANUFACTURER'S SPECIFICATIONS. THE POST-CRASH EXAM REVEALED THAT THE DAMPERS' TORQUE WAS SIGNIFICANTLY BELOW STANDARDS.

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

FLIGHT WITH UNDERTORQUED ROTOR DAMPERS.

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