AM.II.N.K8

From the FAA library

• Helicopter Flying Handbookp. 11-22
  Chapter 11: Helicopter Emergencies and Hazards › System Malfunctions › Low-Frequency Vibrations

  vibrations (100–500 cycles per minute) usually originate from the main rotor disk. The main rotor operational range, depending on the helicopter, is usually between 320 and 500 rpm. A rotor blade that is out of track or balance will ... troubleshoots the source. Out-of-track or out-of-balance main rotor blades, damaged blades, worn bearings, dampers out of adjustment, or worn parts are possible causes of low frequency vibrations…

• Helicopter Flying Handbookp. 11-23
  Chapter 11: Helicopter Emergencies and Hazards › Multiengine Emergency Operations › Single-Engine Failure

  Tracking and Balance Modern equipment used for tracking and balancing the main and tail rotor blades can also be used to detect other vibrations in the helicopter. These systems use accelerometers mounted around the helicopter to detect the direction, frequency ... vibration, and suggest the corrective action. The use of a system such as a health and usage monitoring system (HUMS) provides the operator the ability to record engine and transmission performance and provide rotor track and balance. This system…

• Aviation Maintenance Technician Handbook - Airframep. 2-32
  Chapter 2: Aerodynamics, Aircraft Assembly, & Rigging › Stabilizer Systems › Rotor Blade Preservation & Storage

  brackets. The Vibrex balancing kit is used to measure and indicate the level of vibration induced by the main rotor and tail rotor of a helicopter. The Vibrex analyzes the vibration induced by out-of-track or out-of-balance…