EAD 2014-0085 PZL SW4 Tail Rotor – Push-Pull Rod Spherical Bearings – Inspection / Replacement
[Trouble adding link today, see
EASA Airworthiness Directives Publishing Tool ]
During post flight check of an SW-4 helicopter (military version of PZL SW-4 helicopter), a failure of one spherical bearing of the TR push-pull rod was detected. The affected bearing was found with its outer ring slipped out of the inner spherical race. There were no failure symptoms observed during flight.
Further investigation of the affected TR push-pull rod bearing showed wiping and peeling of the Teflon-steel liner of the inner spherical race which resulted in extensive wear of the bearing. That wear of the affected bearing had not been discovered previously during scheduled DAILY INSPECTIONS and POST-FLIGHT CHECKS, as these only consisted of general visual inspections of the TR for overall condition.
Failure of a spherical bearing causes changes in loading conditions in the TR push-pull rod and can lead to fatigue cracking.
This condition, if not detected and corrected, could lead to structural failure of a TR push-pull rod and consequent loss of the TR anti-torque function, possibly resulting in loss of control of the helicopter.
For the reasons described above, this AD requires repetitive inspections of the TR push-pull rod bearings for condition and no play and, depending on findings, accomplishment of corrective action.