PLT472: Rotorcraft Vibration Sources
What code PLT472 covers, why the FAA tests it, and how to study Rotorcraft Vibration Sources before your checkride.
Recall rotorcraft vibration - characteristics / sources
What this means for your checkride
Because helicopters have many rotating parts, some vibration is inherent, and abnormal vibrations are categorized as low, medium, or high frequency by their source. Low-frequency vibrations, roughly 100 to 500 cycles per minute, usually originate from the main rotor disk, such as a blade out of track or balance, and may be felt through the controls, the airframe, or both. Medium-frequency vibrations, about 1,000 to 2,000 cycles per minute, come from sources like cooling fans and driveline components and are felt through the entire airframe. Most tail rotor vibrations fall into the high-frequency range, about 2,100 cycles per minute or higher, and are felt through the antitorque pedals.
Diagnosing a vibration by its frequency helps a pilot identify the likely source and decide whether continued flight is safe.
A high-frequency vibration felt in the pedals points to the tail rotor, not the main rotor, so matching frequency to source matters.
Where to study it
A code on your test report is an area of deficiency. An authorized instructor must review it with you and endorse that review before you take the practical test, and the examiner may revisit it during the oral. Study it until you can explain it out loud, not just recognize the answer.