Airworthiness Directives; Boeing Model 777 Series Airplanes

This amendment supersedes an existing airworthiness directive (AD), applicable to all Boeing Model 777 series airplanes, that currently requires repetitive testing of the engine fire shutoff switch (EFSS) to determine if the override mechanism and the switch handle are operational, and replacement of the EFSS, if necessary. That AD also requires, for certain airplanes, installation of a collar on a specific circuit breaker of the standby power management panel, and installation of placards to advise the flightcrew that the override mechanism must be pushed in order to pull the fire switch. This amendment adds various actions that would terminate the repetitive testing requirements. This amendment is prompted by a report indicating that a solenoid and an override mechanism of the EFSS were not operational due to overheating of the solenoid. The actions specified by this AD are intended to prevent damage to the EFSS solenoid and to the override mechanism, and consequent failure of the EFSS due to overheating of the solenoid; such failure could result in the inability of the flightcrew to discharge the fire extinguishing agent in the event of an engine fire.