Summary
We propose to supersede Airworthiness Directive (AD) 2006-10- 16, which applies to all The Boeing Company Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747-400D, 747-400F, 747SR, and 747SP series airplanes. AD 2006-10-16 requires, 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, AD 2006-10-16 requires a detailed inspection to determine the type of fasteners, and related investigative actions and repair if necessary. Since we issued AD 2006- 10-16, additional cracking was found in the splice plates, hinge fittings, terminal fittings, the upper skin of the outboard and center sections, and the rear spar webs before reaching the inspection interval specified in AD 2006-10-16. Cracked and fractured Maraging steel fasteners were also found. This proposed AD would reduce the compliance time for certain inspectionsand would add repetitive inspections for cracking of the splice plates, hinge fittings, terminal fittings, the upper skin of the outboard and center sections, and the rear spar webs in Zone B. This proposed AD would also add an inspection to determine whether fasteners are magnetic in Zone C, repetitive ultrasonic inspections for cracking and fractures of affected fasteners, and related investigative and corrective actions if necessary. This proposed AD would also add an optional modification, which would terminate certain repetitive inspections, and would add post-modification inspections and corrective action if necessary. We are proposing 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.