Main Rotor Drive – Main Gearbox Bearing Lock Nut – Replacement
Superseded. Comply with 2021-0121, which replaces this document.
AI-generated summary of the official EASA document. Verify against the PDF before acting.
What to do
Operators must remove affected MGBs and replace bearing lock nuts P/N 3G6320A09151 with P/N 3G6320A09152 within specified compliance times based on helicopter group and accumulated landings, generally by the next MGB overhaul or within 2,000 landings after 12 February 2020. Mixing old and new lock nuts on the same MGB is prohibited from that date. Installation of affected MGBs is restricted after modification or from the effective date for certain groups.
Summary
EASA Airworthiness Directive 2020-0011R1 is an amendment addressing the main gearbox (MGB) bearing lock nut issue on Leonardo S.p.A. AB139 and AW139 helicopters. It mandates replacing the cracked MGB bearing lock nut part number 3G6320A09151 with an improved lock nut part number 3G6320A09152 to prevent potential failure of the MGB planetary gears. The directive applies to all serial numbers of these helicopter models and specifies affected MGB part numbers.
What changed
This revision corrects the listing of certain MGB part and serial numbers in Appendix 1 that were previously misclassified under Group 3 helicopters. It retains the replacement requirements from the original AD but amends compliance times and clarifies installation restrictions for affected MGBs and lock nuts. The directive also prohibits mixing old and new lock nuts on the same MGB assembly from the effective date.
Why it matters
This AD is critical for aviation professionals to prevent potential loss of helicopter control due to failure of the MGB planetary gears caused by cracked bearing lock nuts. Operators and maintenance organizations must ensure timely replacement of affected parts to maintain airworthiness and comply with regulatory requirements. Compliance teams need to track helicopter groups and accumulated landings to apply correct deadlines.
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New ADs and bulletins for Leonardo S.P.A. Helicopters AB139, S.P.A. Helicopters AW139, AB139 and AW139, summarized like this page, every Monday.