Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 747-100, 747-100B, 747-200B, 747-200C, 747- 200F, 747-400F, 747SR, and 747SP series airplanes, without a stretched upper deck or stretched upper deck modification. This proposed AD would require detailed and high-frequency eddy current inspections for cracks at the outboard ends of each affected tension tie and of the surrounding structure, and related investigative and corrective actions if necessary. This proposed AD results from a report of a crack in the tension tie at the body station 820 frame connection, and cracks found on the Boeing 747SR fatigue-test airplane in both the tension ties and frames at the tension tie to frame connections at body stations 800, 820, and 840. We are proposing this AD to find and fix cracks in the tension ties, which could lead to cracks in the skin and body frame and result in rapid in-flight depressurization of the airplane.