AD 99-04-19

This amendment adopts a new airworthiness directive (AD) that is applicable to all Boeing Model 777 series airplanes. This action requires repetitive detailed visual inspections to detect cracking of the cove skin on the outboard leading edge slats; a slat adjustment check; and corrective actions, if necessary. This amendment is prompted by reports of fatigue cracking and/or missing pieces of the cove skin on the outboard leading edge slats. The actions specified in this AD are intended to detect and correct such discrepancies, which could result in skin separation or structural damage to the leading edge slats, and consequent reduced controllability of the airplane.

Final rule; request for comments.

99-04-19 BOEING: Amendment 39-11044. Docket 98-NM-320-AD. \n\n\tApplicability: All Model 777 series airplanes, 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 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 (d) 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 detect and correct cracking and/ormissing pieces of the cove skin on the outboard leading edge slats on the left and right wings, which could result in skin separation or structural damage to the leading edge slats, and consequent reduced controllability of the airplane, accomplish the following: \n\n\tNOTE 2: Where there are differences between the alert service bulletin and the AD, the AD prevails. \n\n\t(a)\tPrior to the accumulation of 500 total flight cycles, or within 30 days after the effective date of this AD, whichever occurs later: Perform a detailed visual inspection to detect cracking of the cove skin on the outboard leading edge slats of the left and right wings at slat numbers 1 through 6 inclusive, and 9 through 14 inclusive; in accordance with Boeing Alert Service Bulletin 777-57A0034, Revision 2, dated November 19, 1998. Repeat the inspection thereafter at intervals not to exceed 350 flight cycles. \n\n\t(b)\tIf any cracking is detected during any inspection required by paragraph (a) of this AD, prior tofurther flight, accomplish the actions specified in paragraph (b)(1), (b)(2), or (b)(3) of this AD, as applicable, in accordance with Boeing Alert Service Bulletin 777-57A0034, Revision 2, dated November 19, 1998. \n\n\t\t(1)\tFor any crack that is less than or equal to 1.5 inches in length, stop drill the crack. Within 5 days following accomplishment of the stop drilling accomplish paragraphs (b)(1)(i) and (b)(1)(ii) of this AD. \n\n\t\t\t(i)\tPerform a detailed visual inspection of the interior structure of the cove skin at slat numbers 1 through 6 inclusive, and 9 through 14 inclusive, in accordance with Part 2 of the Accomplishment Instructions of the alert service bulletin. \n\n\t\t\t\t(A)\tIf no crack is detected, prior to further flight, accomplish a slat adjustment check, and if any slat is not adjusted within the limits, adjust the slat to within the limits; in accordance with Part 3 of the Accomplishment Instructions of the alert service bulletin. \n\n\t\t\t\t(B)\tIf any crack is detected,prior to further flight, replace the slat with a new slat, and accomplish a slat adjustment in accordance with Part 2 of the Accomplishment Instructions of the alert service bulletin. \n\n\t\t\t(ii)\tRepair any cracked cove skin in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. \n\n\t\t(2)\tFor any crack that is greater than 1.5 inches in length, prior to further flight, accomplish paragraphs (b)(2)(i) and (b)(2)(ii) of this AD. \n\n\t\t\t(i)\tPerform the inspection required by paragraph (b)(1)(i) of this AD in accordance with Part 2 of the Accomplishment Instructions of the alert service bulletin. \n\n\t\t\t\t(A)\tIf no crack is detected, prior to further flight, accomplish a slat adjustment check, and if any slat is not adjusted within the limits, adjust the slat to within the limits; in accordance with Part 3 of the Accomplishment Instructions of the alert service bulletin. \n\n\t\t\t\t(B)\tIf any crack is detected, prior to further flight, replace the slat with a new slat and accomplish a slat adjustment in accordance with Part 2 of the Accomplishment Instructions of the alert service bulletin. \n\n\t\t\t(ii)\tRepair any cracked cove skin in accordance with a method approved by the Manager, Seattle ACO. \n\n\t\t(3)\tReplace the slat with a new slat and accomplish a slat adjustment in accordance with Part 2 of the Accomplishment Instructions of the alert service bulletin. \n\n\t(c)\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 ACO. 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 3: 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(d)\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(e)\tThe actions shall be done in accordance with Boeing Alert Service Bulletin 777-57A0034, Revision 2, dated November 19, 1998. 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(f)\tThis amendment becomes effective on March 8, 1999.

The FAA has received several reports of fatigue cracking and/or missing pieces of the cove skin and on the outboard leading edge slats on the left and right wings on Boeing Model 777 series airplanes. On four airplanes that had accumulated between 3,000 and 14,000 flight hours and 650 and 2,800 flight cycles, cracking was located on slat numbers 4, 5, and 9. On one airplane that had accumulated 4,530 total flight hours and 685 total flight cycles, the cracked and missing pieces were located on slat numbers 5 and 10. On another airplane that had accumulated 1,140 total flight hours and 1,525 total flight cycles, a portion of the leading edge wedge was missing, and cracking in the cove skin at the deflection control ribs on slat number 5 was detected. At this time, the exact cause of the cracking is unknown. These conditions, if not detected and corrected, could result in skin separation or structural damage to the outboard leading edge slats, and consequent reduced controllability of the airplane. \n\nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved Boeing Alert Service Bulletin 777-57A0034, Revision 2, dated November 19, 1998, which, among other things, describes procedures for repetitive detailed visual inspections to detect cracking of the cove skin on the outboard leading edge slats; a slat adjustment check to verify proper adjustment of the slat rigging; and corrective actions, if necessary. \n\n\tThe corrective actions include stop drilling of any crack that is 1.5 inches or less as an interim action; replacement of the leading edge slat; and adjustment of the slat, if necessary. Accomplishment of the actions specified in the alert service bulletin 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, thisAD is being issued to detect and correct cracking and/or missing pieces of the cove skin on the outboard leading edge slats on the left and right wings, which could result in skin separation or structural damage to the leading edge slats, and consequent reduced controllability of the airplane. This AD requires accomplishment of the actions specified in the alert service bulletin described previously, except as discussed below. \nDifferences Between This Rule and Alert Service Bulletin \n\n\tThe alert service bulletin specifies that the manufacturer may be contacted for disposition of certain repair conditions. However, this AD requires the repair of those conditions to be accomplished in accordance with a method approved by the FAA. \n\n\tThe alert service bulletin also specifies that the inspection of the interior structure of the cove skin be accomplished repetitively. This AD does not require repetitive interior inspections of this area, because the FAA has determined that the repetitive detailed visual inspections of the exterior structure of the cove skin required by this AD are adequate to detect cracking in the subject area. \n\n\tThe flow chart in Figure 1. of the alert service bulletin does not accurately describe the mandatory corrective actions addressed in this rule. There have been recent instances involving cracking of the slats where it was determined that the slats were properly rigged, therefore, the FAA is uncertain of the cause for the cracking and is not relying on the rigging checks to assure crack free structure. The FAA has determined that the slat adjustment check cited in the flow chart does not adequately address the identified unsafe condition; therefore, this AD does not require accomplishment of this action at the intervals specified. \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: "Comments to Docket Number 98-NM-320-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, 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\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: