EASA AD 2021-0121
Main Rotor Drive — Main Gearbox Bearing Lock Nut — Replacement
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.