On August 10, 1996, a Hughes 269A (registration N8784F) operated by Helicopter Technologies, Inc. was involved in an aviation accident near Cottondale, FL. Investigators recorded the probable cause as: Improper assembly of the main rotor blade dampeners, which led to ground resonance and destruction of the helicopter. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter sustained major damage when ground resonance occurred after liftoff, caused by improperly assembled main rotor blade dampeners that led to severe vibrations and abnormal blade tracking.
Accident Details
Shortly after liftoff, the pilot experienced severe vertical and lateral vibrations. Observing that one rotor blade was tracking 12 to 18 inches out of the normal plane, the pilot initiated a landing. As the helicopter touched down, ground resonance developed, causing the aircraft to break apart.
Maintenance Findings
An FAA inspector examined the main rotor blade dampeners, which had been overhauled just before the flight. The inspection revealed that the dampeners had not been reassembled in accordance with the manufacturer's maintenance manual.
Manufacturer's Guidance
The maintenance manual explicitly stated that improper assembly of the blade dampeners could lead to ground resonance and destruction of the helicopter. The observed failure sequence matched this warning.
Probable cause
Improper assembly of the main rotor blade dampeners, which led to ground resonance and destruction of the helicopter.