AD 2021-02-03 Requires Various Repetitive Inspections Of The Main Rotor (MR) Damper

The FAA is adopting a new airworthiness directive (AD) for certain Leonardo S.p.a. (Leonardo) Model AW189 helicopters.

This AD requires various repetitive inspections of the main rotor (MR) damper. This AD was prompted by reports of in-service MR damper failures and the development of an improved MR damper. This condition, if not corrected, could lead to loss of the lead-lag damping function of the MR blade, possibly resulting in damage to adjacent critical rotor components and subsequent loss control of the helicopter. The actions of this AD are intended to address the unsafe condition on these products. This AD is effective April 1, 2021.

Supplementary Information: The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to Leonardo Model AW189 helicopters with MR damper part number (P/N) 4F6220V00251 installed. The NPRM published in the Federal Register on May 20, 2020 (85 FR 30664). The NPRM proposed to require reducing the installation torque of the nuts on the bolts attaching the MR damper to the MR hub. The NPRM also proposed to require, at specified intervals, replacing the affected MR damper; dye penetrant or eddy current inspecting the rod  end and body end of each MR damper for a crack, visually inspecting the rod end and body end of each MR damper for a crack, and replacing any cracked MR damper. For certain helicopters, the NPRM also proposed to require inspecting each rod end and body end bearing for rotation, and replacing the rod end or MR damper as applicable if there is any rotation; inspecting the lag damper broached ring nut for damage, correct engagement, and alignment and removing the rod end and broached ring nut from service if any of those conditions exist. For all helicopters, the NPRM proposed to require, at specified intervals, inspecting the bearing friction torque of each MR damper body end and rod end, and replacing the MR damper if the torque value exceeds 30.0 Nm (265.5 lb in); inspecting the MR damper anti-rotation block for wear and replacing the anti-rotation block if there is wear beyond acceptable limits; and replacing each special washer P/N 3G6220A05051 with special washer P/N 3G6220A05052. For certain MR dampers, the NPRM proposed to require inspecting the broached ring for damage and alignment, removing the broached ring from service if there is damage, and replacing the broached ring if the rod end and broached ring cannot be aligned.

Finally, the NPRM proposed to require inspecting certain serial-numbered MR dampers for correct torque of the broached ring prior to installation on any helicopter. The proposed requirements were intended to detect a crack in an MR damper, which if not detected and corrected, could lead to loss of the leadlag damping function of the MR blade, resulting in damage of the MR damper, detachment of the MR damper in-flight, and subsequent loss of control of the helicopter.

The NRPM was prompted by EASA AD No. 2016-0145R1, dated January 17, 2018 (EASA AD 2016-0145R1), issued by EASA, which is the Technical Agent for the Member States of the European Union, to correct an unsafe condition for Leonardo Model AW189 helicopters with MR damper P/N 4F6220V00251 installed. EASA advises that a MR damper failed, which resulted in complete seizure of the body end lug and an in-flight disconnection of the damper. EASA states  that a combination of factors may have contributed to the MR damper disconnection, and that this condition could result in loss of the lead-lag damping function of the MR blade, damage to adjacent critical rotor components, and subsequent reduced control of the helicopter. The contributing factors include cracks, slippage marks, damaged broach ring teeth, and loss of torque.

According to EASA, the AW189 MR damper is a similar design to the MR dampers installed on Model AW139 helicopters, where multiple MR damper failures have been reported involving the body end lug, the eye end lug, and the rod end. To correct this condition, EASA issued a series of superseded and revised ADs to require repetitive inspections of certain MR dampers, and similar corrective actions as those for Model AW139 helicopters. EASA AD 2016-0145R1 requires various one-time and repetitive inspections of the MR damper, a torque check of the body end, and replacing any MR damper with a crack or that fails the torque check. EASA AD 2016-0145R1 also allows installation of a new MR damper, P/N 8G6220V00151, as an optional terminating action for the repetitive inspections.

FMI: www.regulations.gov