Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 747-400F series airplanes. This proposed AD would require initial detailed and open-hole high frequency eddy current inspections for cracking of the web, upper chord, and upper chord strap of the upper deck floor beams, and repair of any cracking. This proposed AD also would require a preventive modification of the upper deck floor beams, and repetitive inspections for cracking after accomplishing the modification. This proposed AD is prompted by reports of fatigue cracking found on the upper deck floor beam to frame attachment points. We are proposing this AD to prevent fatigue cracks in the upper chord, upper chord strap, and the web of the upper deck floor beams and resultant failure of the floor beams. Failure of a floor beam could result in damage to critical flight control cables and wire bundles that pass through the floor beam, and consequent loss of controllability of the airplane. Failure of the floor beam also could result in the failure of the adjacent fuselage frames and skin, and consequent rapid decompression of the airplane.