Summary
We propose to supersede airworthiness directive (AD) 2007-16- 19, which applies to certain The Boeing Company Model 747-200B, 747- 300, and 747-400 series airplanes. AD 2007-16-19 requires repetitive detailed inspections for cracking of the aft tension tie channels from body station (BS) 1120 to BS 1220 and from BS 880 to BS 1100, and corrective actions if necessary, and optional terminating action. Since we issued that AD, analysis has indicated the need to mandate the previously optional modification. This proposed AD would retain the existing requirements, limit the area of the detailed inspection, add repetitive surface high-frequency eddy current inspections, and mandate the previously optional terminating action. We are proposing this AD to prevent fatigue cracking of the tension ties, which could result in reduced structural integrity of the airplane and rapid depressurization of the airplane.