Airworthiness Directives; Boeing Model 747 Series Airplanes

This amendment supersedes two existing airworthiness directives (AD) that are applicable to certain Boeing Model 747 series airplanes. One of those AD's currently requires inspections for cracking, corrosion, and fracturing of the lower horizontal clevis of the strut midspar fittings, and replacement of discrepant parts with new or serviceable parts, or repair, if necessary. That AD also requires inspection for removal of broken sealant of the clevis and the fasteners, and various follow-on actions. It also provides for optional terminating actions for the inspections. The other AD currently requires inspection for cracking of certain fastener holes of the upper and lower horizontal clevis legs. This amendment continues to require inspections to detect cracking, corrosion, and fracturing of the lower horizontal clevis; and adds corresponding inspections of the upper horizontal clevis, and replacement of discrepant parts with new parts, or rework, if necessary. This amendment also removes certain optional terminating actions. This amendment is prompted by reports of cracking of the lower and upper leg of the horizontal clevis of the midspar fitting. The actions specified in this AD are intended to detect and correct cracking and fracturing of the clevis, which could result in drooping of the strut at the strut-to-wing interface, and consequent separation of the engine and strut from the airplane.