Summary
We propose to supersede airworthiness directive (AD) 84-19-01, which applies to certain The Boeing Company Model 747-100, 747-200B, 747-200F series airplanes. AD 84-19-01 requires repetitive inspections for cracking of certain tension ties, and repair and certain modifications if necessary. Since we issued AD 84-19-01, the upper deck tension ties have been identified as structure that is susceptible to widespread fatigue damage (WFD), and additional action is necessary for certain airplanes to adequately address the identified unsafe condition on the fleet. This proposed AD is intended to complete certain mandated programs intended to support the airplane reaching its limit of validity (LOV) of the engineering data that support the established structural maintenance program. For certain airplanes, this proposed AD would add inspections for cracking of the tension tie at body station (BS) 760 or 780, corrective action if necessary, and eventual modification of the tension ties.For all airplanes, this proposed AD would require repetitive post-modification inspections for cracking of the tension tie at BS 760 or 780, and corrective action if necessary. We are proposing this AD to detect and correct tension tie cracking, which could eventually result in in-flight depressurization of the airplane and the inability to withstand current regulatory failsafe loads.