Summary
The FAA proposes to adopt a new airworthiness directive (AD) for all Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747- 200C, 747-300, 747-400, 747-400D, and 747SR series airplanes. This proposed AD would require a one-time inspection to determine whether any steel doubler (small or large) is installed at the lower forward and upper aft corners of the fuselage cutout at main entry doors (MEDs) number 3. Depending on the results of this inspection, this proposed AD also would require repetitive inspections for cracks of the skin, bearstrap, and small steel doubler (if installed) at the applicable corner or corners of the fuselage cutouts, and related investigative/ corrective actions if necessary. This proposed AD also would provide the optional terminating action for the repetitive inspections of installing a large steel doubler at the affected corners. This proposed AD is prompted by reports of cracks in the skin and bearstrap at the upper aft corner and at the lower forward corner of the fuselage cutout at MEDs number 3. We are proposing this AD to detect and correct cracks in the skin, bearstrap, and small steel doubler (if installed), which could propagate and result in rapid decompression of the airplane.