Airworthiness Directives; Boeing Model 777 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 777 series airplanes, that requires repetitive inspections of the safety spring wear plate doublers attached to the auxiliary power unit (APU) firewall, measurement of wear of the doublers, and follow-on actions, if necessary. For certain airplanes, this amendment also requires a one-time inspection to detect improper clearance between the safety spring wear plate doubler and the APU firewall, and corrective action, if necessary. This amendment also provides for optional terminating action for the repetitive inspections. This amendment is prompted by reports indicating that excessive wear was found on the safety spring wear plate doublers on the APU firewall of Boeing Model 777 series airplanes. The actions specified by this AD are intended to detect and correct wear of the safety spring wear plate doublers on the APU firewall, which could result in a hole in the APU firewall, and consequent decreased fire protection capability.