EASA 2019-0046

Requires modification of the main gearbox (MGB) tail rotor (TR) drive flange. This AD stems from reports of several occurrences of loss of tightening torque of the Shur-Lok nut, which serves as a retainer of the MGB TR drive. Subsequent investigation determined that these events were the result of failure of the Shur-Lok nut locking function, which is normally ensured by two anti-rotation tabs engaged into two slots at the end of the MGB output shaft pinion. EASA previously issued and later revised AD 2014-0179 to require a one-time inspection of the radial play inside the TR rotor drive flange and the condition of the Shur-Lok nut and, depending on findings, accomplishment of applicable corrective action(s). Since EASA AD 2014-0179R2 was issued, a further occurrence was reported of on-ground loss of synchronization of the tail rotor, resulting from Shur-Lok disengagement. Prompted by this new occurrence, EASA decided to make the modification mandatory.