CEN15LA156

The commercial pilot was conducting an on-demand air taxi helicopter flight. The pilot reported that, while in cruise flight over water, the helicopter experienced an abrupt, uncommanded left yaw. The pilot returned to the departure airport and performed a run-on landing. A postflight examination of the helicopter revealed that one of the tail rotor pitch change links (PCL) was fractured. A review of maintenance records revealed that the fractured PCL had recently been overhauled and installed on the helicopter and that it failed 14.8 flight hours since overhaul. Examination of the PCL revealed that it had fractured due to undetected fatigue cracking that appeared to be the result of bending loads caused by stiff bearings. The stiffness was likely the result of the lack of control of the bearing replacement process. The PCL bearing replacement procedures, which incorporated rotational torque inspection and bearing staking procedures, were contained in the overhaul manual; these procedures were revised about 3 months before the accident, and the overhaul facility used the revised procedures during the replacement of the PCL. Examination of the PCL revealed that both of the bearings exceeded the maximum allowable rotational torque by at least two times the maximum allowed. Based on the findings of this investigation, the PCL manufacturer corrected the figure in the PCL replacement procedures to display the correct method of inspecting spherical bearing rotational torque.

On February 20, 2015, about 0750 central standard time, an Agusta A119 Mk II helicopter, N802SM, experienced an abrupt, uncommanded left yaw during cruise flight over the Gulf of Mexico. The pilot and passenger were not injured. The helicopter sustained substantial damage. The helicopter was registered to and operated by Era Helicopters LLC., under the provisions of 14 Code of Federal Regulations Part 135 as an on-demand air taxi flight. Visual meteorological conditions prevailed for the flight which operated on a company visual flight rules flight plan. The flight departed the Houma-Terrebonne Airport (HUM), Houma, Louisiana, at 0720 and was en route to an off-shore platform.After the uncommanded left yaw, the pilot returned to HUM and performed a run-on landing. A post-flight inspection of the helicopter revealed one of the tail rotor pitch change links (PCL) was fractured. While no further damage was sustained to any helicopter components, the fractured pitch change link had an adverse effect on the helicopter's flight characteristics and required replacement meeting the definition of substantial damage. The tail rotor pitch change link (PCL) assembly comprises a single-piece cast aluminum body with two circular ends, each end containing a spherical bearing. The PCL end connected to the tail rotor blade contains the larger of the two spherical bearings, and is identified as the "large bearing" in this report. The PCL end connected to the tail rotor pitch change mechanism is identified as the "small bearing" in this report. A review of maintenance documentation found that the fractured PCL was overhauled by Precision Heliparts (PHP) and issued an authorized release certificate on December 8, 2014. It was installed on N802SM on February 13, 2015. The fractured pitch link failed at 14.8 flight hours since overhaul and 1,129.8 of total flight hours. Representatives from the National Transportation Safety Board (NTSB), AgustaWestland, PHP, Era Helicopters, and the Federal Aviation Administration convened at Agusta Westland facilities in Philadelphia, Pennsylvania to evaluate the bearing friction for the tail rotor PCLs. The method of inspecting PCL bearing rotational torque was found in the maintenance manual (MM) and overhaul manual (OM). The earlier version of the OM, dated November 25, 2012, differed from the more recent version of the OM, dated November 10, 2014. The 2012 version of the OM required rotational torque inspection by rotating the inspection tool, a 100 millimeter (mm) lever arm, about the axis of the bearing bolt hole, while the 2014 version of the OM required the inspection tool to be rotated away from the axis of the bearing bolt hole. This revision changed the bearing staking procedure. The bearing replacement procedures between the 2012 and 2014 versions of the OM remained the same. AgustaWestland identified the 2012 version of the OM contained the correct bearing rotational torque inspection method. PHP identified they hadused the 2014 version of the bearing rotational torque inspection method. During the postaccident examination of the accident PCL, the 2012 and the 2014 inspection procedures were used to measure rotational torque. Both the large and small bearings of fractured PCL exceeded the maximum allowable bearing rotational torque either measured with 2012 and 2014 procedure. For the fractured PCL, the 2012 inspection method consistently returned a higher rotational torque value than the 2014 inspection method. The fractured PCL was examined by the NTSB Material Laboratory. The fracture surface exhibited evidence of fatigue that originated at a raised dash that was part of the part number marking on the PCL. The materials laboratory characterized fatigue cracking across 60% to 70% of the fracture cross section. For additional details on the materials laboratory examination see the Materials Laboratory Factual Report in the docket for this investigation. On March 4, 2015, the FAA issued emergency airworthiness directive (EAD) No. 2015-05-52 for owners and operators of certain A109-series and AW119-series helicopters to inspect PCL part number 109-0130-05-117 for freedom of movement, corrosion, excessive friction of the spherical bearings, and cracks. FAA EAD No. 2015-05-52 was prompted by European Aviation Safety Agency (EASA) issuance of EASA EAD No. 2015-0035-E on February 27, 2015. According to AgustaWestland and the FAA, there have been no reports to date of tail rotor PCL spherical bearings exhibiting excessive friction after inspection directed via the aforementioned FAA and EASA EADs. Based on the findings of this investigation, AgustaWestland had corrected the figure in the replacement procedures to display the correct method of inspecting spherical bearing rotational torque. Additionally, the PCL bearing replacement procedures were removed from the MM and are now found only within the OM.