The FAA has received several reports of cracks found in the lower gate hinge on the forward galley service door on Boeing Model 737 series airplanes. In two of these cases, the hinge was severed completely and the lower gate separated from the airplane while in flight, which resulted in loss of cabin pressure. In one of these cases, the emergency escape slide was slowly pulled through the gate opening, and, subsequently, it separated from the airplane. These airplanes had accumulated between 13,700 and 66,000 total flight cycles. Investigation revealed that the cause of such cracking was due to fatigue. The effects of such fatigue cracking could lead to the failure of the lower gate hinge on the forward galley service door and subsequent loss of cabin pressure. If the hinge fails, the hinge and its associated mechanisms and the emergency escape slide could separate from the airplane and be ingested into the engine, or could strike and damage the flight control surfaces. Explanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved Boeing Alert Service Bulletin 737-52A1124, dated January 11, 1996, which describes procedures for repetitive detailed visual inspections to detect cracks of the lower gate hinge of the forward galley service door, and replacement of any cracked hinge found. The service bulletin also describes procedures for replacement of the lower gate hinge of the forward galley service door with an improved hinge, which will eliminate the need for the repetitive inspections.\n\n Explanation of the Requirements of the AD \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other Boeing Model 737 series airplanes of the same type design, this AD is being issued to prevent fatigue cracking and subsequent failure of the lower gate hinge on the forward galley service door. This AD requires repetitive detailed visual inspections to detect cracks of the lower gate hinge of the forward galley service door, and replacement of any cracked hinge found. This AD also provides for an optional replacement of the lower gate hinge of the forward galley service door with an improved hinge, which constitutes terminating action for the repetitive inspection requirements. The actions are required to be accomplished in accordance with the alert service bulletin described previously. \n\nDifferences Between the AD and the Relevant Service Information \n\n\tOperators should note that, unlike the various recommended compliance times specified in the alert service bulletin for accomplishing the initial inspection of airplanes (specified as 1,200 flight cycles after receipt of the service bulletin for airplanes with 10,000 to 12,000 total flight cycles; 800 flight cycles after receipt for airplanes with 12,000 to 13,000 total flight cycles; and 400 flight cycles after receipt for airplanes with 13,000 or more total flight cycles), this AD requires that all airplanesbe inspected within 400 flight cycles after the effective date of the AD. In consideration of not only the manufacturer's recommendation, but the degree of urgency associated with addressing the subject unsafe condition, the average utilization of the affected fleet, and the time necessary to perform the inspection (3 hours), the FAA has determined that the various intervals specified in that alert service bulletin would not address the identified unsafe condition in a timely manner. In addition, the FAA has reviewed the available data and determined that the length of cracking is not necessarily related to the airplane's flight cycles, but instead is related to the number of door cycles. In light of all of these factors, the FAA finds that a 400-flight cycle compliance time for initiating the required actions is warranted, in that it represents an appropriate interval of time allowable for affected airplanes to continue to operate without compromising safety. \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: "Comments to Docket Number 96-NM-84-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 copyof 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\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 USC 106(g), 40113, 44701. § 39.13 - (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: