Summary
We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 747-200B, 747-300, 747-400, 747-400D, and 747-400F series airplanes. This proposed AD was prompted by a report of cracking in both the aluminum strut side skin, and corrosion resistant steel (CRES) outer spring beam support fitting. This proposed AD would require repetitive high frequency eddy current (HFEC) inspections for cracking in the strut side skin; an open-hole HFEC inspection for cracking, applicable related investigative and corrective actions; and a fastener installation modification. We are proposing this AD to detect and correct cracking of the strut side skin; such cracking could result in the failure of the outer spring beam support fitting, which could cause separation of a strut and engine from the airplane during flight.