Rotor inspection, vibration and usage evidence
Rotor and transmission maintenance depends on measured condition, applicable limits, history and the actual configuration. Begin with the reported symptom, its frequency and the operating condition. A vibration label is a clue rather than a unique part diagnosis. This chapter concerns interpretation and controlled maintenance evidence, not a generic procedure for running or adjusting a helicopter.
Track and balance
Tracking compares blade-tip paths against a specified reference and tolerance. Mass balance concerns the distribution of mass and moments. Aerodynamic differences, rotor speed, control settings and installation can also affect rotating behavior. A correct static balance does not prove correct dynamic behavior, while equal tracking does not independently establish that all blade moments match.
Dynamic measurement uses the defined sensors, phase reference and operating conditions. Once-per-revolution and blade-passing components refer to the stated rotor, so main-rotor and tail-rotor references must not be confused. Compare frequency with the relevant component speed before assigning a likely source. A high amplitude can have several causes and should not automatically trigger an improvised weight or pitch-link adjustment.
Condition and material
Blade skins, spars, retention parts, bearings, dampers and couplings carry different loads and need different inspections. Composite damage can involve debonding or internal separation that exterior appearance alone does not establish. Tap testing, penetrant, eddy-current, magnetic-particle or ultrasonic methods each have a defined application and limitations. The actual inspection data and personnel qualification determine which method and acceptance criteria apply.
A life-limited component can require retirement at its defined limit even if it looks undamaged. Conversely, remaining life does not prove that impact, corrosion or an exceedance can be ignored. Track identification, accumulated usage and any required event evaluation. Do not invent a universal inspection suite for every hard landing, lightning event or rotor strike.
Monitoring and records
HUMS combines appropriate sensor and usage information to support detection and trending. It does not guarantee that every failure will be predicted, and a reassuring trend is not permission to disregard a chip indication or actual damage. Magnetic chip detectors primarily respond to relevant ferrous material; a clean detector cannot rule out every nonferrous failure or lubricant problem.
Oil level, temperature, pressure, debris and maintenance history provide complementary evidence. Follow the applicable response and test instructions rather than infer a universal dry-run duration or landing permission. Record measured results, corrections, tools and outstanding discrepancies accurately, preserving required independent checks. Only the authorized process and complete applicable evidence can support a return-to-service decision.