Main Rotor Drive — Main Gearbox Bearing Lock Nut — Replacement
- Published
- Effective
- Deadline
- Replaces
- 2020-0011R1
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. Mixing of old and new lock nuts on the same MGB is prohibited. Installation of affected MGBs is restricted after modification or from the effective date for unaffected groups. Compliance must be achieved by 18 May 2021 or within the defined landing limits.
Summary
EASA Airworthiness Directive 2021-0121 is an airworthiness directive addressing the replacement of main gearbox (MGB) bearing lock nuts on Leonardo AB139 and AW139 helicopters. It applies to all serial numbers of these helicopter models with specific affected MGB part numbers. The directive mandates replacing the cracked or potentially cracked bearing lock nut P/N 3G6320A09151 with an improved design P/N 3G6320A09152 to ensure continued safe operation.
What changed
This directive supersedes EASA AD 2020-0011R1 and expands the scope to include additional affected MGB part numbers, specifically P/N 3G6320A00136 with certain serial numbers. It retains the requirement to replace the older bearing lock nuts with the redesigned version that reduces stress and cracking risk. The compliance times and installation restrictions are updated accordingly.
Why it matters
The replacement of the MGB bearing lock nuts is critical to prevent failure of the planetary gears within the main gearbox, which could lead to loss of helicopter control. For operators and maintenance organizations, compliance ensures continued airworthiness and safety of AB139 and AW139 helicopters. The directive provides clear instructions and deadlines to avoid unsafe conditions related to cracked lock nuts.
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