AD 2021-22-16 Requires Replacing The MGB, Or As An Alternative, Replacing The Epicyclic Reduction Gear Module

The FAA is adopting a new airworthiness directive (AD) for Airbus Helicopters Model EC 155B and EC155B1 helicopters.

This AD was prompted by the failure of a main gearbox (MGB) second stage planet gear. This AD requires replacing the MGB, or as an alternative, replacing the epicyclic reduction gear module for certain serial numbered planet gear assemblies installed on the MGB. This AD also requires inspecting the MGB magnetic plugs and MGB filter for  particles, and for certain serial-numbered planet gear assemblies, inspecting the oil sump for particles.

Depending on the outcome of these inspections, this AD requires further inspections and replacing certain parts. This AD also prohibits installing certain parts. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective January 3, 2022.

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 EC 155B and EC155B1 helicopters. The NPRM published in the Federal Register on July 22, 2021 (86 FR 38608). In the NPRM, the FAA proposed to require for helicopters with at least one Type Y planet gear assembly with a certain serial number (S/N) installed, or at least one Type Z planet gear assembly with a certain S/N installed, within 10 hours time-in-service (TIS) after the effective date of the AD and thereafter at intervals not to exceed 10 hours TIS, inspecting the MGB magnetic plugs for particles. If there  are particles, the NPRM proposed to require further inspections and analyses and replacing the MGB, depending on the type and the size of the particles.

The NPRM also proposed to require for helicopters with a Type Y planet gear assembly with a certain S/N installed, within 25 hours TIS after the effective date of the AD, inspecting the MGB filter for particles. If there are particles, the NPRM proposed to require further inspections and analyses and replacing the MGB, depending on the type and the size of the particles. The NPRM proposed to require for helicopters with at least one Type Y planet gear assembly with a certain S/N installed, within 50 hours TIS after the effective date of the AD, replacing the MGB. As an alternative to replacing the MGB, the NPRM would allow replacing the epicyclic reduction gear in the affected MGB.

Additionally, the NPRM proposed to require, for helicopters without any Type Y planet gear assembly but at least one Type Z planet gear assembly with a certain S/N installed, replacing the MGB within 50 hours TIS after the effective date of the AD or before any planet gear assembly accumulates 1,800 total hours TIS, whichever occurs later. As an alternative to replacing the MGB, the NPRM would allow replacing the epicyclic reduction gear in the affected MGB.

The NPRM also proposed to require, for helicopters with at least one Type Z planet gear with a certain S/N installed, within certain compliance times specified in the figures in this AD, inspecting the MGB filter and inspecting the oil sump for particles. If there are particles, the NPRM proposed to require further inspections and analyses, and replacing the MGB, depending on the type and the size of the particles.

The NPRM also proposed to prohibit installing an MGB with a certain serial numbered Type Y planet gear assembly and proposed to prohibit installing a Type Y planet gear assembly with a certain S/N on any helicopter.

Additionally, the NPRM proposed to prohibit installing certain serial numbered Type Z planet gear assemblies that have accumulated 1,800 or more total hours TIS and prohibit installing an MGB with certain serial numbered Type Z planet gear assemblies that have accumulated 1,800 or more total hours TIS.

Finally, the NPRM proposed to prohibit installing an MGB if the type of the planet gear assembly cannot be  determined and also prohibit installing any planet gear assembly if the type cannot be determined.

The NPRM was prompted by EASA AD 2018-0263, dated December 7, 2018 (EASA AD 2018-0263), issued by EASA, which is the Technical Agent for the Member States of the European Union, to correct an unsafe condition for Airbus Helicopters Model EC 155 B and EC 155 B1 helicopters. EASA advises that after an accident on a Model EC225 helicopter, an investigation revealed the failure of an MGB second stage planet gear. EASA states that one of the two types of  planet gear used in the MGB epicyclic module is subject to higher outer race contact pressures and therefore is more susceptible to spalling and cracking. This condition, if not addressed, could result in failure of a MGB planet gear assembly, failure of the MGB, and subsequent loss of helicopter control.

Accordingly, EASA AD 2018-0263 requires repetitive inspections of the MGB magnetic plugs, the MGB filer, and the oil sump for particles, and depending on the results of those inspections, removing or replacing certain parts. EASA AD 2018-0263 also requires reducing the life limit of Type Z planet gear assemblies. EASA AD 2018-0263 also requires, if certain gear assemblies are installed, either replacing the MGB or replacing the epicyclic reduction gear.

Finally, EASA AD 2018-0263 prohibits installing a Type Y planet gear assembly or an MGB with a Type Y planet gear assembly on any helicopter.

FMI: www.regulations.gov