The FAA has received a report indicating that the flight crew of a Boeing Model 747-200 series airplane heard a loud noise below the cockpit area during flight descent. The flight continued with an uneventful landing. Investigation revealed that the left-hand side wall of the nose wheel well (NWW) was bulging. Further investigation revealed that the fuselage frames at body stations (BS) 300 and BS 320 had severed approximately 10 inches outboard of the NWW side panel. Additionally, the vertical beam of the NWW at BS 300 contained multiple cracks in the inner chord, a severed web, and a cracked and deformed outer chord. The vertical beam of the NWW at BS 320 also was found to have a severed web and cracks in the radius of the inner chord, as well as severe damage to numerous horizontal stiffeners and clips. The apparent cause of this cracking is fatigue. \n\n\tFatigue cracking of the BS 300 and BS 320 fuselage frames in the area of the NWW, if not detected and corrected in a timely manner, could result in collapse of the NWW pressure bulkhead, and subsequent rapid decompression of the airplane. \n\nOther Relevant Rulemaking \n\n\tThe FAA previously issued AD 90-06-14, amendment 39- 6544 (55 FR 10045, March 19, 1990), which is applicable to certain Boeing Model 747 series airplanes. (A correction of that rule was published in the Federal Register on May 18, 1990 (55 FR 20590).) That AD requires repetitive visual inspections to detect fatigue cracking of the vertical beams, webs, clips, side wall web, top panel and intercostals of the NWW. That AD requires that the initial inspection be accomplished prior to the accumulation of 10,000 total flight cycles, and that repetitive inspections be accomplished at intervals of 1,500 or 3,000 flight cycles, depending on the inspection method used. \n\n\tThe FAA also issued AD 91-11-01, amendment 39-6997 (56 FR 22306, May 15, 1991), which also is applicable to certain Boeing Model 747 series airplanes. That AD requires the inspection to detect fatigue cracking of the fuselage frames adjacent to the NWW, prior to the accumulation of 16,000 flight cycles. That AD provides an optional terminating modification that entails installing new fuselage frames (including the frames adjacent to the NWW) with improved durability. That modification is required prior to the accumulation of 20,000 flight cycles in accordance with AD 90-06-06 (aging fleet AD). \n\n\tThe airplane involved in the incident described previously had accumulated 14,341 total flight cycles at the time of structural failure. A visual inspection to detect cracking of the vertical beams of the NWW in accordance with AD 90-06-14 had been performed only 621 cycles prior to the reported failure. The fuselage frames in its NWW area had not yet been replaced with the new, improved durability frames in accordance with AD 91-11-01. \n\nExplanation of the Requirements of the Rule \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other Boeing Model 747 series airplanes of the same type design, this AD is being issued to detect and correct fatigue cracking of BS 300 and BS 320 fuselage frames adjacent to the NWW, which could result in collapse of the NWW pressure bulkhead and possibly result in rapid decompression of the airplane. This AD requires repetitive visual inspections to detect fatigue cracking of the inner chord and web of the left and right side of fuselage frames at BS 300 and BS 320, from the NWW side panel outboard to stringer 39. This AD also requires a one-time visual inspection to detect fatigue cracking of the vertical beam webs and chords of the NWW at BS 300 and BS 320. This AD also requires that any cracking detected during those inspections be repaired in accordance with a method approved by the FAA. \n\nInterim Action \n\n\tThis is considered to be interim action until final action is identified, at which time the FAA may consider further rulemaking.\n\n Determination of Rule's Effective Date \n\n\tSince a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days. \n\nComments Invited \n\n\tAlthough this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed. \n\n\tComments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket. \n\n\tCommenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 96-NM-279-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \n\n\tThe regulations adoptedherein will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. \n\n\tThe FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES." \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Safety. \n\nAdoption of the Amendment \n\n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows: \n\nPART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. § 39.13 - (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: