Airworthiness Directives; Boeing Model 777 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to all Boeing Model 777 series airplanes, that requires either a one-time inspection or a review of the airplane maintenance records for both stabilizer trim control modules (STCM) of the trim system of the horizontal stabilizer to determine if STCMs having certain serial numbers are installed; and follow-on corrective actions, if necessary. This amendment also requires eventual replacement of affected STCMs with new or reworked STCMs, which would terminate the follow-on actions. The actions specified by this AD are intended to prevent an uncommanded stabilizer trim due to simultaneous failure of two static seals on one STCM, combined with failure of the automatic shutdown function of the stabilizer trim system. Such failures could result in loss of pitch control and consequent loss of control of the airplane. This action is intended to address the identified unsafe condition.