AD 96-24-03 SUPERSEDED

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing 747-400 series airplanes in the "combi" configuration. This action requires replacing the decompression panels that are located in the smoke barrier between the passenger and main deck cargo compartment, with new panels of an improved design. This amendment is prompted by reports indicating that normal pressurization cycles are causing premature tearing or opening of these decompression panels. The actions specified in this AD are intended to prevent increased airflow in the cargo compartment caused by the tearing or opening of these panels; this condition, if not corrected, could result in delayed fire detection and reduced effectiveness of the cargo compartment fire suppression system.

Final rule; request for comments

96-24-03 BOEING: Amendment 39-9829. Docket 96-NM-255-AD. \n\n\tApplicability: Model 747-400 "combi" airplanes; as listed in Boeing Alert Service Bulletin 747- 25A3064, dated December 21, 1995; on which a 90-minute fire suppression system specified in paragraph (b)(4) of AD 93-07-15, amendment 39-8547, has been installed; certificated in any category. \n\n\tNOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been otherwise modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (b) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent increased airflow in the cargo compartment caused by the tearing or opening of the decompression panels, which could result in delayed fire detection and reduced effectiveness of the fire suppression system, accomplish the following: \n\n\t(a)\tWithin 90 days after the effective date of this AD, replace the decompression ("blow-out") panels in the smoke barrier above the cargo/passenger partition, with improved panels, in accordance with Boeing Alert Service Bulletin 747-25A3064, dated December 21, 1995. \n\n\t(b)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO. \n\n\tNOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. \n\n\t(c)\tSpecial flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished. \n\n\t(d)\tThe replacement shall be done in accordance with Boeing Alert Service Bulletin 747-25A3064, dated December 21, 1995. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. \n\n\t(e)\tThis amendment becomes effective on December 9, 1996.

The FAA has received at least four reports indicating that tearing and inadvertent opening of the decompression ("blow-out") panels located in the smoke barrier between the passenger and main deck cargo compartment have occurred on Boeing Model 747-400 "combi" airplanes. One operator reported that the decompression panel on one of its airplanes tore and inadvertently opened during service. A subsequent survey indicated that three other operators had experienced similar in-service incidents. Investigation has revealed that fatigue associated with normal pressurization cycles is causing the premature tearing of the decompression panels. \n\n\tTearing and subsequent opening of these decompression panels allows additional air to flow into the cargo compartment. In the event of a fire in the cargo compartment, the additional airflow would dilute the smoke and, consequently, result in delayed detection of the fire. Additionally, the increased airflow would dilute the cargo compartment fire suppression agent below effective concentrations and, thus, degrade the capability of the system to suppress a fire. \n\n\tThis condition is significant specifically for airplanes that are equipped with a "90-minute fire suppression system" installed in accordance with "Option 4" of paragraph (b)(4) of AD 93-07-15, amendment 39-8547 (58 FR 21243, April 20, 1993). That AD requires various actions that are intended to minimize the hazards associated with a fire occurring in the main deck Class B cargo compartment. Paragraph (b)(4) of AD 93-07-15 requires, among other things, installing a cargo compartment fire extinguishing system in the Class B cargo compartment that ". . . provides an initial fire extinguishant concentration of at least 5% of the empty compartment volume of Halon 1301 or equivalent, and a fire suppression extinguishant concentration of at least 3% of the empty compartment volume of Halon 1301 or equivalent, for a period of time not less than 90 minutes." \n\n\tIf additional air flows into the cargo compartment through a torn or open panel and dilutes the amount of extinguishant, it would reduce the effectiveness of the 90-minute fire suppression system. \n\nExplanation of Relevant Service Information \n\n\tBoeing has issued Alert Service Bulletin 747-25A3064, dated December 21, 1995, which describes procedures for replacing the currently-installed decompression panels with new panels of an improved design. \n \nThe new panels are more resistant to tearing and inadvertent opening.\n\n Explanation of 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, this AD is being issued to prevent tearing and inadvertent opening of the decompression panels that are located in the smoke barrier between the passenger and main deck cargo compartment. This AD requires the replacement of certain panels with new panels having an improved design. The actions are required to be accomplished in accordance with the service bulletin described previously. \n\n\tThis AD is applicable only to airplanes that are equipped with a 90-minute fire suppression system, which is specified as "Option 4" in paragraph (b)(4) of AD 93-07-15.\n\n Cost Impact \n\n\tNone of the Model 747-400 "Combi" airplanes affected by this action are on the U.S. Register. All airplanes included in the applicability of this rule currently are operated by non-U.S. operators under foreign registry; therefore, they are not directly affected by this AD action. However, the FAA considers that this rule is necessary to ensure that the unsafe condition is addressed in the event that any of these subject airplanes are imported and placed on the U.S. Register in the future. \n\n\tShould an affected airplane be imported and placed on the U.S. Register in the future, it would require approximately 1 work hour to accomplish the required actions, at an average labor charge of $60 per work hour. Required parts would cost approximately $14,000 per airplane. Based on these figures, the cost impact of this AD would be $14,060 per airplane. \n\nDetermination of Rule's Effective Date \n\n\tSince this AD action does not affect any airplane that is currently on the U.S. register, it has no adverse economic impact and imposes no additional burden on any person. Therefore, prior notice and public procedures hereon are unnecessary and the amendment may be made effective in less than 30 days after publication in the Federal Register. \n\nComments Invited \n\n\tAlthough this action is in the form of a final rule and was not preceded by notice and 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-255-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\tFor the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria ofthe Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it 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\n PART 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:

Submit comments in triplicate to the Federal Aviation Administration (FAA),\nTransport Airplane Directorate, ANM-103, Attention: Rules Docket No. 96-NM-255-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.\n\n\tThe service information referenced in this AD may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Susan Letcher, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-2670; fax (206) 227-1181.