Helicopter Experiences Tail Rotor Issues During Offshore Platform Landing (N430CV)

Incident Details

A commercial helicopter pilot with 17,291 hours of flight experience was on short final approach to a helipad on an offshore platform when he heard and felt a "bump" in the flight controls. This was followed by vibrations in the tail rotor pedals and a loss of tail rotor effectiveness. The pilot immediately landed the helicopter and performed a normal engine cool-down. Inspection of the helipad found no evidence of a tail rotor strike.

Inspection Findings

A post-accident inspection of the studs that hold the tail rotor gearbox to the tail boom revealed signs of low-cycle bending fatigue. Additional microscopic examination of the studs showed evidence of high loads during bending. The 90-degree tail rotor gearbox teeth displayed a typical wear pattern and did not show any sign of misalignment. One of the tail-rotor blades was heavily damaged and missing a portion of the outer blade. The remaining end of the blade was slightly torn and contained gray paint or material at the leading edge. The material was later examined and found to contain a high concentration of zinc. Examination of paint chips in the impact area on the vertical fin showed no zinc in the paint. The object that impacted the tail rotor blade could not be identified or located during the course of the investigation.