Airworthiness Directives; Boeing Model 747 Airplanes

The FAA is superseding two existing airworthiness directives (ADs); one AD is applicable to all Boeing Model 747 airplanes and the other AD is applicable to certain Boeing Model 747 airplanes. The first AD currently requires repetitive inspections for cracking of the upper skin of the horizontal stabilizer center section and the rear spar upper chord, and repair if necessary. The other AD currently requires repetitive inspections for cracking of the upper skin of the outboard and center sections of the horizontal stabilizer and the rear spar structure, hinge fittings, terminal fittings, and splice plates; and repair if necessary. This new AD adds, for certain airplanes, repetitive inspections for cracking of the outboard and center sections of the horizontal stabilizer and repair if necessary. For certain other airplanes, this new AD adds a detailed inspection to determine the type of fasteners, related investigative actions, and repair if necessary. This new AD also revises the compliance times for certain inspections and adds alternative inspections for cracking of the upper skin of the center section and rear spar upper chord. This AD results from reports of cracking in the outboard and center section of the aft upper skin of the horizontal stabilizer, the rear spar chord, rear spar web, terminal fittings, and splice plates; and a report of fractured and cracked steel fasteners. We are issuing this AD to detect and correct this cracking, which could lead to reduced structural capability of the outboard and center sections of the horizontal stabilizer and could result in loss of control of the airplane.