The FAA has received a report that, during a periodic heavy maintenance check of a Boeing Model 737-300 series airplane equipped with a main deck cargo door installed in accordance with Supplemental Type Certificate SA2969SO, cracks were found in the upper jamb area of the fuselage and in the main cargo door. The cracks were between 0.50 inches and 2.35 inches in length. The cause of such cracking is unknown at this time. However, several scenarios (e.g., improper cargo door operations during loading and unloading of cargo, and improper fastener locations) are being examined at this time to determine a possible cause of the cracking.\n\n\tCracking in the upper jamb area of the fuselage or in the main deck cargo door, if not corrected, could result in reduced structural integrity of the main deck cargo door and/or fuselage, and consequent loss or opening of the main deck cargo door while the airplane is in flight, or reduced controllability of the airplane. \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 737-200 and -300 series airplanes, equipped with a main deck cargo door installed in accordance with Supplemental Type Certificate SA2969SO, of the same type design, this AD is being issued to detect and correct cracking in the upper jamb area of the fuselage and in the main deck cargo door; such cracking could result in reduced structural integrity of the main deck cargo door and/or fuselage, and consequent loss or opening of the main deck cargo door while the airplane is in flight, or reduced controllability of the airplane. This AD requires repetitive detailed visual inspections to detect cracks in the hinge and lift actuator box area of the main deck cargo door and upper jamb of the fuselage; and replacement of any cracked part with a new part having the same part number, or repair in accordance with a method approved by theFAA. \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\nDetermination 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: "Commentsto Docket Number 98-NM-30-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \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\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: