We are adopting a new airworthiness directive (AD) for certain Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747- 300, 747-400, 747-400D, and 747SR series airplanes. For certain airplanes, this AD requires a material type inspection to determine if the lower forward corner reveal of the number 3 main entry doors (MEDs) is a casting. If the reveals are castings, this AD requires repetitive inspections of the reveals for cracking, and corrective action if necessary. If the reveals are not castings, this AD requires a detailed inspection of the reveals for a sharp edge and repetitive inspections of the reveals for cracking, and corrective action if necessary. For certain other airplanes, this AD requires only a detailed inspection of the reveals for a sharp edge and repetitive inspections of the reveals for cracking, and corrective action if necessary. For certain other airplanes, this AD requires repetitive inspections of the reveals for cracking only, and corrective action if necessary. This AD also allows a certain replacement as an optional action for the material type inspection for certain airplanes. This AD results from reports of cracking and/or a sharp edge in the lower forward corner reveal of the number 3 MEDs. We are issuing this AD to detect and correct fatigue cracking of the lower forward corner reveal of the number 3 MEDs, which could lead to the door escape slide departing the airplane when the door is opened and the slide is deployed, and consequent injuries to passengers and crew using the door escape slide during an emergency evacuation.