On September 12, 1984, an Agusta A109 (registration N57BL) was involved in an aviation accident near Clifton, AZ. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced violent vibrations after landing, leading to tail rotor ground contact and main gear collapse. Investigation found no pre-accident part failure or malfunction.
Accident Details
The pilot reported that the helicopter landed firmly on the main ramp and entered the two-minute cool-down mode for engine shutdown. Immediately after retarding the power levers to idle, the pilot felt a slight lateral movement of the controls, which was followed by an accelerated lateral movement of the helicopter. The helicopter then entered a violent lateral and forward vibration. The pilot shut off the engine and applied the rotor brake, but before the vibration stopped, the tail rotor assembly struck the ground and the main landing gear collapsed.
Investigation
No pre-accident part failure or malfunction was found that would have resulted in the vibration or ground resonance. The investigation did not identify any mechanical or structural issues that could have caused the event.