Recently, two operators reported finding fatigue cracks in the fuselage frames below the lower jamb of the main deck cargo door between stringers 20L and 21L at water line 180 on Boeing Model 737-300 series airplanes. The cracking was randomly located in various areas of the fuselage frames and may have initiated at frame stations 380, 400, 420, 440, 460, and/or 480 at the radius of the frame webs that were modified in accordance with supplemental type certificate (STC) SA2969SO. \n\n\tSuch cracking, if not detected and corrected in a timely manner, could result in rapid decompression of the airplane. \n\n\tPemco Aeroplex installed main deck cargo doors on Boeing Model 737-200 and -300 series airplanes in accordance with STC SA2969SO. Therefore, the FAA has determined that Boeing Model 737-200 series airplanes are also subject to the same unsafe condition. \n\n\tThe FAA has reviewed and approved Pemco Alert Service Letter 737-53-0004, dated January 10, 1995, which describes procedures for detailed close visual inspections to detect cracking of the fuselage frames below the lower jamb of the upper deck main cargo door between stringers 20L and 21L at water line 180 at frame stations 380, 400, 420, 440, 460, and 480, and repair of any cracking found. \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design, this AD is being issued to prevent rapid decompression of the airplane due to cracking of the fuselage frames below the lower jamb of the upper deck main cargo door. This AD requires detailed close visual inspections to detect cracking of the fuselage frames below the lower jamb of the upper deck main cargo door, and repair, if necessary. The actions are required to be accomplished in accordance with the alert service letter described previously. \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\t(NOTE: The FAA previously issued AD 95-01-06, amendment 39-9117 (60 FR 2323, January 9, 1995), which is applicable to the same airplanes affected by this new AD action. AD 95-01-06 requires inspections to detect cracking in the radii on the support angles on the lower jamb (latch lug fittings) of the main cargo door, and replacement of cracked parts. The requirements of AD 95-01-06 are different and separate from the requirements of this new AD.) \n\n\tAs a result of recent communications with the Air Transport Association (ATA) of America, the FAA has learned that, in general, some operators may misunderstand the legal effect of AD's on airplanes that are identified in the applicability provision of the AD, but that have been altered or repaired in the area addressed by the AD. The FAA points out that all airplanes identified in the applicability provision of an AD are legally subject to the AD. If an airplane has been altered or repaired in the affected area in such a way as to affect compliance with the AD, the owner or operator is required to obtain FAA approval for an alternative method of compliance with the AD, in accordance with the paragraph of each AD that provides for such approvals. A note has been included in this rule to clarify this long-standing requirement. \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\n Comments 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 Docketnumber 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 95-NM-23-AD." The postcard will be date stamped and returned to the commenter. \n\n\tThe regulations adopted herein 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\n List of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.\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\n PART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1.\tThe authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. § 39.13 - (Amended) \n\n\t2.\tSection 39.13 is amended by adding the following new airworthiness directive: