Main Rotor Drive – Main Gearbox Bearing Lock-Nut – Replacement
Superseded. Comply with 2020-0011R1, which replaces this document.
- Published
- Effective
- Deadline
- Replaces
- 2019-0036
AI-generated summary of the official EASA document. Verify against the PDF before acting.
What to do
Operators must remove the affected main gearbox from service and replace the bearing lock-nut P/N 3G6320A09151 within the specified compliance times based on accumulated landings or during the next MGB overhaul, whichever occurs first. If landing data is unavailable, flight hours should be converted to landings by multiplying by six. Installation of serviceable MGBs or affected MGBs with less than 28,000 landings is allowed provided the lock-nut replacement is completed as required.
Summary
EASA Airworthiness Directive 2019-0174 is an airworthiness directive issued for Leonardo S.p.A. AB139 and AW139 helicopters. It addresses the replacement of the main gearbox (MGB) bearing lock-nut part number 3G6320A09151 to prevent potential failure of the MGB planetary gears. This directive applies to all serial numbers of AB139 and AW139 helicopters equipped with affected main gearboxes.
What changed
EASA Airworthiness Directive 2019-0174 supersedes AD 2019-0036 and introduces reduced compliance times for replacing the affected MGB bearing lock-nut. It retains the original replacement requirements but mandates earlier action due to additional occurrences of cracked bearing lock-nuts. The directive also clarifies installation conditions for affected parts and provides credit for prior replacements done according to the original service bulletin.
Why it matters
This directive is critical for aviation professionals as it addresses a safety issue that could lead to loss of helicopter control due to failure of the main gearbox planetary gears. Operators and maintenance organizations must ensure timely replacement of the affected bearing lock-nut to maintain airworthiness and regulatory compliance. Compliance teams need to track landing counts and overhaul schedules to meet the revised deadlines and avoid operational disruptions.
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