Excessive medium frequency vibration could be caused by a/an _______________________ or improperly mounted equipment.

Excessive medium frequency vibration could be caused by a/an _______________________ or improperly mounted equipment.

• A. Unbalanced main rotor head
• B. Tail rotor drive system malfunction
• C. Main gearbox suspension malfunction
• D. Engine malfunction

Answer: (C)

Medium-frequency vibration is often tied to how the drivetrain is mounted and damped to the airframe. If the main gearbox suspension is worn or not properly installed, the gearbox isn’t adequately isolated from the fuselage and can excite the mid-band resonances as gear mesh and shafts load and unload during flight. This creates a noticeable vibration in the medium-frequency range transmitted through the structure. Improper mounting of other equipment can also cause vibration, but the gearbox suspension fault directly links to the drivetrain’s resonant energy, making it the most likely cause. Unbalanced main rotor head tends to produce vibration at the rotor speed and its harmonics, typically not in the mid-frequency range; tail rotor drive issues tend to show different patterns tied to the tail rotor RPM; engine problems usually manifest differently, often tied to engine speed or misfire characteristics rather than mid-band drivetrain resonance.

Medium-frequency vibration is often tied to how the drivetrain is mounted and damped to the airframe. If the main gearbox suspension is worn or not properly installed, the gearbox isn’t adequately isolated from the fuselage and can excite the mid-band resonances as gear mesh and shafts load and unload during flight. This creates a noticeable vibration in the medium-frequency range transmitted through the structure. Improper mounting of other equipment can also cause vibration, but the gearbox suspension fault directly links to the drivetrain’s resonant energy, making it the most likely cause. Unbalanced main rotor head tends to produce vibration at the rotor speed and its harmonics, typically not in the mid-frequency range; tail rotor drive issues tend to show different patterns tied to the tail rotor RPM; engine problems usually manifest differently, often tied to engine speed or misfire characteristics rather than mid-band drivetrain resonance.