PLT265: Ground Resonance Corrective Action
What code PLT265 covers, why the FAA tests it, and how to study Ground Resonance Corrective Action before your checkride.
Recall helicopter takeoff / landing - ground resonance action required
What this means for your checkride
If ground resonance begins, the required action depends on rotor rpm. When the rpm is low, the only corrective action is to close the throttle immediately and fully lower the collective to put the blades in low pitch. When the rpm is in the normal operating range, fly the helicopter off the ground so the blades can rephase themselves automatically, then make a normal touchdown. Do not let the helicopter firmly recontact the surface before the blades realign, because a second shock can aggravate the unbalanced condition into a violent, uncontrollable oscillation.
Ground resonance can destroy a helicopter in seconds, so the pilot must apply the correct action instantly based on rpm.
There is no single fix: the response differs entirely depending on whether rotor rpm is low or in the normal operating range.
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.