Five operators of McDonnell Douglas Model DC-9-81 (MD-81), DC-9-82 (MD-82), DC-9-83 (MD-83), DC-9-87 (MD-87), and Model MD-88 airplanes reported instances of a shock strut cylinder of a main landing gear (MLG) fracturing, resulting in the MLG collapse during landing roll out. The airplanes had a shock strut cylinder of the MLG that fractured after accumulating between a total of 6,386 and 28,100 landings. The fractures began at cracks on the outer surface of the cylinders. The cracks were created by high stresses from vibration that can occur during airplane braking. Failure of the shock strut cylinders of the MLGs due to cracking could lead to collapse of the MLGs and consequent reduced controllability of the airplane during landing. \n\nSimilar Condition Exists on Other Models \n\n\tThe shock strut cylinders on certain McDonnell Douglas Model MD-90- 30 airplanes are identical to those on the affected Model DC-9-81 (MD- 81), DC-9-82 (MD-82), DC-9-83 (MD-83),and DC-9-87 (MD-87) airplanes; and Model MD-88 airplanes. Therefore, those Model MD-90-30 airplanes may be subject to the unsafe condition due to exchanging a shock strut cylinder of a MLG from an affected airplane. \n\nRelated Rulemaking \n\n\tAD 99-06-13, amendment 39-11077 (64 FR 13330, March 18, 1999), applicable to certain McDonnell Douglas Model DC-9-80 series airplanes; and Model MD-88 airplanes, requires repetitive inspections to detect fatigue cracking of the shock strut cylinder of the MLG and replacement of any cracked shock strut cylinder with a serviceable part. That AD references McDonnell Douglas Alert Service Bulletin MD80-32A286, Revision 03, dated May 28, 1998, as the applicable source of service information. \n\n\tAD 96-01-09, amendment 39-9485 (61 FR 2407, January 26, 1996), applicable to certain McDonnell Douglas Model DC-9-80 series airplanes and Model MD-88 airplanes, requires installation of hydraulic brake line restrictors on the MLG, and modification of the hydraulic damper assembly of the MLG. That AD references McDonnell Douglas Service Bulletins MD80-32-276, dated March 31, 1995, and Revision 1, dated October 17, 1995; and MD80-32-278, dated March 31, 1995, and Revision 1, dated September 6, 1995; as the applicable sources of service information. \n\nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved Boeing Alert Service Bulletin MD80-32A344, Revision 2, dated January 28, 2004, for McDonnell Douglas Model DC-9-81 (MD-81), DC-9-82 (MD-82), DC-9-83 (MD-83), DC-9-87 (MD- 87) airplanes; and Model MD-88 airplanes; and Boeing Alert Service Bulletin MD90-32A059, dated January 28, 2004, for McDonnell Douglas Model MD-90-30 airplanes. These alert service bulletins specify verification of airplane records to determine service history of the shock strut cylinders of the MLGs. These alert service bulletins describe procedures for repetitive inspections (including performing fluorescent dye penetrant and fluorescent dryparticle non- destructive testing) to detect cracking of the shock strut cylinders of the left and right MLGs, and replacement of any cracked shock strut cylinder with a new or serviceable part. Additionally, these alert service bulletins describe certain related investigative actions (such as chemically removing cadmium coating, and repeating the fluorescent dye penetrant and fluorescent magnetic particle non-destructive test inspections, if necessary). \n\n\tAccomplishment of the actions specified in the alert service bulletins is intended to adequately address the identified unsafe condition. \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 airplanes of the same type design registered in the United States, this AD is being issued to prevent failure of the shock strut cylinders of the MLGs due to cracking, which could result in collapse of the MLG and consequent reduced controllability duringlanding. This AD requires repetitive inspections to detect cracking of the shock strut cylinders of the left and right MLGs, and replacement of any cracked shock strut cylinder with a new or serviceable part. This AD also requires that, if a replacement shock strut cylinder is not new, the service history of the shock strut cylinder determines the applicability by Group definition in the applicable service bulletin described previously. This AD requires accomplishment of the actions specified in the alert service bulletins described previously, except as discussed below. \n\nDifferences Between the Service Bulletins and the Airworthiness Directive \n\n\tAlthough Boeing Alert Service Bulletin MD80-32A344, Revision 2, dated January 28, 2004, specifies that McDonnell Douglas Alert Service Bulletin MD80-32A286, Revision 03, dated May 28, 1998, be accomplished prior to Boeing Alert Service Bulletin MD80-32A344, Revision 2, this AD does not require that action. As described in the "Related Rulemaking" section, accomplishment of Boeing Alert Service Bulletin MD80-32A286, Revision 03, is already required by AD 99-06-13. \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\tSubmit comments using the following format: \n\nOrganize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues. \nFor each issue, state what specific change to the AD is being requested. \nInclude justification (e.g., reasons or data) for each request. \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 2003-NM-122-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \n\n\tThe regulations adopted herein will not have a substantial direct effect 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, it is determined that this final rule does not have federalism implications under Executive Order 13132. \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, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\nAccordingly, 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\n1. The authority citation for part 39 continues to read as follows: \n\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 (Amended) \n\n2. Section 39.13 is amended by adding the following new airworthiness directive: