Bell Helicopter Textron Canada 429 accident near Port O'Connor, Texas, August 21, 2015

The NTSB's narrative final · quoted from the NTSB record

The commercial pilot reported that, during cruise flight in the helicopter, he felt a "slight vibration" and heard a "very faint bumping sound." A flight control check revealed no anomalies, and the pilot continued the flight to the destination heliport. While in a 4-ft hover, just before touching down, the helicopter began a slow, uncommanded right turn. The pilot applied full left anti-torque pedal, and the turn stopped. He then lowered the collective and landed without incident. A post-flight inspection of the helicopter revealed that one of the tail rotor outboard pitch change links (PCL) was broken. An examination of the failed PCL revealed fatigue fractures due to pitting corrosion between the spherical bearing and the bearing housing. The fatigue fractures propagated during operation until the PCL bearing housing fractured, separating the PCL from the blade pitch horn end spherical bearing, resulting in a loss of pitch control to the affected blade. The PCL was installed on the helicopter 12 days before the manufacturer issued an alert service bulletin (ASB) introducing a 50-hour recurrent inspection of the tail rotor PCLs for axial and radial bearing play. About 6 months later, the Federal Aviation Administration (FAA) subsequently issued an emergency airworthiness directive (EAD) based on the ASB. The tail rotor PCLs on the accident helicopter were inspected in accordance with the ASB and the EAD 9 days after the EAD was issued. The PCL failed 6.6 flight hours after the inspection. The EAD did not require an inspection of the bearing housing portion of the PCL for corrosion, and it could not be determined if the fatigue cracks were present when the inspection was performed. Following the accident, the manufacturer updated the original ASB to include inspections for bearing cracks, corrosion, and anti-corrosion sealant. The FAA also updated the airworthiness directive to reflect the additional inspections.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.