Summary
We are revising an earlier proposed airworthiness directive (AD) for all The Boeing Company Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747-400D, 747-400F, 747SR, and 747SP series airplanes. The original NPRM proposed a general visual inspection to identify any existing structural repair manual repairs of the upper main sill outer chord of the left and right side main entry door number 1, as applicable; repetitive detailed inspections for cracks in the upper main sill of the door(s); and related investigative and corrective actions, if necessary. The original NPRM also proposed repetitive inspections for airplanes on which a certain repair is done, and corrective actions if necessary. The original NPRM was prompted by reports of cracks in the main entry door number 1 upper main sill outer chord, along the bend radius of the chord on several airplanes. This action revises the original NPRM by reducing certain compliance times. We are proposing this supplemental NPRM to detect and correct cracks in the main entry door number 1 upper main sill outer chord, along the bend radius of the chord, which could result in loss of structural integrity of the airplane. Since these actions impose an additional burden over that proposed in the original NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.