Agusta Aerospace Corp AW119 MKII N802SM accident near Gulf Of Mexico

Probable cause

The fracture of the tail rotor pitch change link due to excessive bearing rotational friction, which resulted from the bearings being installed in exceedance of the maximum allowable torque during the last overhaul of the pitch change link.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for CEN15LA156 for the full record.