AD 2020-23-06 Requires Inspecting The Main Rotor (M/R) Hub Assembly (Hub) Phonic Wheel Lock Washer

The FAA is adopting a new airworthiness directive (AD) for Airbus Helicopters Model AS332C, AS332C1, AS332L, and AS332L1 helicopters.

This AD requires inspecting the main rotor (M/R) hub assembly (hub) phonic wheel lock washer (lock washer) for correct installation and depending on the outcome, repairing or replacing the M/R hub. This AD was prompted by reported occurrences of M/R revolutions per minute (“NR”) sensor fluctuations. The actions of this AD are intended to address an unsafe condition on these products. This AD is effective December 24, 2020.

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 Airbus Helicopters Model AS332C, AS332C1, AS332L, and AS332L1 helicopters with an M/R hub part number (P/N) 332A31-0001-00, 332A31-0001-01, 332A31-0001-02, 332A31-0001-03, 332A31-0001-04, 332A31-0001-05, or 332A31-0001-06 installed. The NPRM published in the Federal Register on July 16, 2020 (85 FR 43160). The NPRM proposed to require removing at least one M/R “NR” sensor and borescope inspecting the phonic wheel lock washer for correct height of the lock washer. The NPRM also proposed to prohibit the installation of an affected M/R hub unless it has successfully passed the required inspection for correct lock washer installation.

The proposed requirements were intended to prohibit the incorrect assembly of the M/R hub, which, if not corrected, could result in failure of the M/R hub components and subsequent loss of control of the helicopter.

The NPRM was prompted by EASA AD No. 2019-0172, dated July 18, 2019, issued by EASA, which is the Technical Agent for the Member States of the European Union. This EASA AD was issued to correct an unsafe condition for Airbus Helicopters Model AS 332 C, AS 332 C1, AS 332 L, and AS 332 L1 helicopters with an M/R hub P/N 332A31-0001-00, 332A31-0001-01, 332A31-0001-02, 332A31-0001-03, 332A31-0001-04, 332A31-0001-05, or 332A31-0001-06 installed. EASA advises of reported occurrences of “NR” sensor fluctuation and subsequent investigation identifying incorrect positioning of the M/R hub phonic wheel due to incorrect installation of the M/R mast nut press screws during maintenance of the M/R hubs. EASA advises that this condition, if not detected and corrected, could lead to failure of M/R hub components, possibly resulting in loss of helicopter control. Accordingly, the EASA AD requires a one-time inspection of the lock washer position and depending on findings, replacing the M/R hub.

FMI: www.regulations.gov