Summary
We propose to supersede Airworthiness Directive (AD) 2013-14- 05, which applies to certain The Boeing Company Model 747-400 and 747- 400F series airplanes. AD 2013-14-05 currently requires repetitive inspections of the longeron extension fittings for cracking, and related investigative and corrective actions if necessary. AD 2013-14- 05 also provides optional terminating action for the repetitive inspections. Since we issued AD 2013-14-05, we determined that more work is necessary on airplanes on which a terminating action (permanent repair, longeron extension fitting replacement, or modification) was accomplished. This proposed AD would continue to require the requirements of AD 2013-14-05, and would add new repetitive high frequency eddy current (HFEC) inspections of any modified, repaired, or replaced longeron extension fitting for cracking, and applicable related investigative and corrective actions if necessary. We are proposing this AD to detect and correct cracks in thelongeron extension fittings, which can become large and adversely affect the structural integrity of the airplane.