Summary
We propose to adopt a new airworthiness directive (AD) for certain Model 747-200B, -300, -400, -400D, and -400F series airplanes. This proposed AD would require an inspection to determine the part number of the door and to determine if the correct mid-pivot access door is installed, and the installation of a marker on the mid-pivot access door, and if necessary, repetitive ultrasonic inspections for cracking of the mid-pivot bolt assembly and eventual replacement of the mid-pivot bolt assembly. This proposed AD results from a report that the left and right spring beam mid-pivot bolt assembly access doors for the No. 1 strut were inadvertently installed in the incorrect position during strut modification. We are proposing this AD to detect and correct incorrectly installed mid-pivot bolt assemblies on the spring beam on the outboard struts. Incorrectly installed bolt assemblies could lead to fatigue cracking and consequent fracturing of the mid- pivot bolt assembly, which couldlead to loss of the spring beam load path and the possible separation of a strut and engine from the airplane during flight.