Vibrations are caused by out-of-balance forces. The source of the out-of-balance condition may be unequal rotor mass distribution, inadequate blade tracking, and or unbalanced drive train components.
The owner or operator is responsible for maintaining the aircraft in an airworthy condition.
At a minimum, all aircraft need an annual inspection. If the aircraft is used for hire, a 100-hour inspection is needed as well. Depending on aircraft, the transponder and pitot-static system may need to be inspected as well.
The transponder needs to be tested every 24 months.
Batteries need to be replaced when the ELT has been used more than one cumulative hour or 50 percent of the useful charge or life has expired.
Airworthiness directives are legally enforceable rules that apply to aircraft, aircraft engines, propellers, and appliances.
The required instruments for VFR flight during the day include airspeed indicator, altimeter, magnetic direction indicator, tachometer, manifold pressure gauge, oil pressure gauge, oil temperature gauge and fuel gauge.
If the equipment is not required, the item should be disabled and placarded as inoperative.
The following documents are required to be in the aircraft during flight. Airworthiness certificate, registration, radio operators permit (if outside the U.S.), operating limitations, and weight and balance. The mnemonic ARROW is often used to remember these documents.
No. The helicopter is not airworthy with any dents in a monocoque tailboom.