AD 99-01-10

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that currently requires repetitive inspections to detect discrepancies of the diagonal brace lugs of the engine strut, and rework of the diagonal brace lugs, if necessary. That AD also provides an option to defer the rework for certain cases by accomplishing repetitive inspections and resealing the bushing. That AD also provides for an optional terminating modification for the repetitive inspections. This amendment adds a requirement to repetitively inspect a new area of the diagonal brace of the engine strut. For certain airplanes, this amendment also adds new repetitive inspections of the subject area and requires that certain previously required repetitive inspections be accomplished at reduced intervals. This amendment is prompted by reports of fatigue or stress corrosion cracking in new areas of the diagonal brace. The actions specified inthis AD are intended to prevent such fatigue or stress corrosion cracking, which could result in failure of the strut and consequent separation of the engine from the airplane.

Final rule; request for comments.

99-01-10 BOEING: Amendment 39-10976. Docket 98-NM-327-AD. Supersedes AD 97-19-08, Amendment 39-10128. \n\n\tApplicability: Model 747 series airplanes having line positions 1 through 1046 inclusive; certificated in any category; equipped with Pratt & Whitney Model JT9D series engines, General Electric Model CF6-45 and -50 series engines, or Rolls Royce Model RB211 series engines; excluding those airplanes on which modifications of the strut/wing structure have been accomplished in accordance with one of the following AD's: \n\n\t AD 95-10-16, amendment 39-9233, or \n\t AD 95-13-05, amendment 39-9285, or \n\t AD 95-13-07, amendment 39-9287. \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 (l)(1) 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 fatigue and stress corrosion cracking in the diagonal brace, which could result in failure of the strut and consequent separation of the engine from the airplane, accomplish the following: \n\nRESTATEMENT OF REQUIREMENTS OF AD 97-19-08: \n\n\t(a) For airplanes identified as Groups 1, 2, 3, and 4 in Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997: Perform a detailed visual and ultrasonic inspection to detect cracking, corrosion, and migrated or rotated bushings of the diagonal brace lugs, in accordance with and at the times specified in Table 1 of Figure 1 of Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, or Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997; except that where the service bulletin states that an inspection is to be performed within a specified number of days after receipt of the service bulletin, the inspection shall be accomplished within that number of days after September 29, 1997 (the effective date of AD 97-19-08, amendment 39-10128). Thereafter, repeat the inspections of the diagonal brace lug as specified in paragraph (a)(1) or (a)(2) of this AD, as applicable, until the inspections required by paragraph (e) have been accomplished. \n\n\t\t(1) For the aft diagonal brace lug: Repeat the detailed visual and ultrasonic inspections thereafter at intervals not to exceed those specified in paragraph (d) or (e) in Table 1 of Figure 1 of the service bulletin, as applicable. \n\n\t\t(2) For the forward diagonal brace lug: Repeat the detailed visual and ultrasonic inspections thereafter at intervals not to exceed 600 landings. These inspections on the forward diagonal brace lug must be accomplished in accordance with 747 Non-Destructive Test (NDT) Manual D6-7170, Part 4, Subject 54-40-05.\n\n\tNOTE 2: Where there are differences between the AD and the referenced service bulletins, the AD prevails. \n\n\t(b) For airplanes identified as Groups 3, 4, and 5 in Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997: Perform a detailed visual and ultrasonic inspection to detect cracking, corrosion, or migrated or rotated bushings of the diagonal brace lugs, in accordance with and at the times specified in Table II of Figure 1 of Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, or Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997; except that, where the service bulletin states that an inspection is to be performed within a specified number of days after receipt of the service bulletin, the inspection shall be accomplished within that number of days after September 29, 1997. Repeat the detailed visual and ultrasonic inspections thereafter at intervals not to exceed 1,000 flight cycles, until the inspections required by paragraph (f) have been accomplished. \n\n\t(c) If any migrated or rotated bushing is detected during any of the inspections required by paragraph (a) or (b) of this AD, prior to further flight, rework the diagonal brace lug, in accordance with Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, or Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997; except as provided in paragraph (d) of this AD. Thereafter, repeat the detailed visual and ultrasonic inspections required by paragraph (a) of this AD prior to the accumulation of 5,000 landings, and/or repeat the detailed visual and ultrasonic inspections required by paragraph (b) of this AD prior to the accumulation of 9,000 landings. If the lug bore diameter is not within the rework limits, prior to further flight, replace the diagonal brace or repair it, in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate; or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative (DER) who has been authorized by the Manager, Seattle ACO, to make such findings. \n\n\t(d) In lieu of accomplishing the requirements of paragraph (c) of this AD, perform an ultrasonic inspection to detect cracking or corrosion of the diagonal brace lug, in accordance with Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, or Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997. \n\n\t\t(1) If no other damage is detected during the inspection required by paragraph (d) of this AD, prior to further flight, reseal the bushings or apply corrosion-inhibiting compound in accordance with the service bulletin; and thereafter, repeat the inspections of the diagonal brace lug as specified in paragraph (d)(1)(i) or (d)(1)(ii) of this AD, as applicable. If corrosion-inhibiting compound is applied, repeat the application at intervals not to exceed 9 months, in accordance with the service bulletin. Within 15 or 18 months (as applicable in the service bulletin) since the initial detection of the migrated or rotated bushing, rework the diagonal brace lug in accordance with the service bulletin; and thereafter, repeat the detailed visual and ultrasonic inspections required by paragraph (a) of this AD prior to the accumulation of 5,000 landings and/or repeat the detailed visual and ultrasonic inspections required by paragraph (b) of this AD prior to the accumulation of 9,000 landings. If the lug bore diameter is not within the rework limits, prior to further flight, replace the diagonal brace or repair it, in accordance with a method approved by the Manager, Seattle ACO, or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company DER who has been authorized by the Manager, Seattle ACO, to make such findings. \n\n\t\t\t(i) For the aft diagonal brace lug: Repeat the detailed visual and ultrasonic inspections required by paragraphs (a) and (b) of this AD thereafter at intervals not to exceed those specified in paragraph (d) or (e) in Table 1 and paragraph (d) of Table II of Figure 1 of the service bulletin, as applicable; except that the repetitive detailed visual inspections are required within 9 months following accomplishment of the resealing or application of corrosion-inhibiting compound. \n\n\t\t\t(ii) For the forward diagonal brace lug: Repeat the detailed visual and ultrasonic inspections required by paragraphs (a) and (b) of this AD thereafter at the repetitive intervals specified in those paragraphs, as applicable; except that the repetitive detailed visual inspections are required within 9 months following accomplishment of the resealing or application of corrosion-inhibiting compound. These inspections on the forward diagonal brace lug must be accomplished in accordance with 747 NDT Manual D6-7170, Part 4, Subject 54-40-05. \n\n\t\t(2) If any cracking or corrosion is detected during the inspection required by paragraph (d) of this AD, prior to further flight, rework the diagonal brace lug in accordance with the service bulletin; and thereafter, repeat the detailed visual and ultrasonic inspections required by paragraph (a) of this AD prior to the accumulation of 5,000 landings, and/or repeat the detailed visual and ultrasonic inspections required by paragraph (b) of this AD prior to the accumulation of 9,000 landings. If the lug bore diameter is not within the rework limits, prior to further flight, replace the diagonal brace or repair it, in accordance with a method approved by the Manager, Seattle ACO, or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company DER who has been authorized by the Manager, Seattle ACO, to make such findings. \n\nNEW REQUIREMENTS OF THIS AD: \n\n\t(e) For airplanes identified as Groups 1, 2, 3, and 4 in Boeing Alert Service Bulletin 747-54A2126, Revision 7, dated November 20, 1998: Perform detailed visual, high frequency eddy current (HFEC), and ultrasonic inspections, as applicable, to detect cracking, corrosion, and migrated or rotated bushings of the diagonal brace lugs or of the root radius of the clevis of the diagonal brace, in accordance with Table 1 of Figure 1 of Revision 7 of the alert service bulletin, at the time specified in paragraph (e)(1) or (e)(2) of this AD, whichever occurs later. Repeat the inspections thereafter at the times specified in Table 1 of Figure 1 of Revision 7 of the alert service bulletin. Accomplishment of the applicable inspections constitutes terminating action for the repetitive inspection requirements of paragraphs (a)(1) and (a)(2) of this AD. For airplanes on which any migrated or rotated bushing was detected during any inspection required by paragraph (a) of this AD, but on which the rework required by paragraph (c) of this AD has not been accomplished, accomplishment of the inspections required by paragraph (e) of this AD constitutes terminating action only for the repetitive inspection requirements of paragraph (d)(1) of this AD. However, rework of the diagonal brace lug in accordance with paragraph (d)(1) of this AD is still required within 15 or 18 months after the initial detection of the migrated or rotated bushing; repetitive detailed visual inspections are required within 9 months after accomplishment of the resealing or application of corrosion-inhibiting compound; and, if corrosion-inhibiting compound was applied in lieu of resealing the bushings in accordance with paragraph (d)(1) of this AD, reapplication of the corrosion-inhibiting compound is required at intervals not to exceed 9 months. \n\n\t\t(1) Inspect prior to the accumulation of 5,000 total flight cycles; or within 5,000 flight cycles after rework of the diagonal brace lugs in accordance with Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, or Revision 7, or Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997. Or \n\n\t\t(2) Inspect within 150 flight cycles or 60 days after the effective date of this AD, whichever occurs first. \n\n\t(f) For airplanes identified as Groups 3, 4, and 5 in Boeing Alert Service Bulletin 747-54A2126, Revision 7, dated November 20, 1998: Perform detailed visual, HFEC, and ultrasonic inspections; as applicable; to detect cracking, corrosion, and migrated or rotated bushings of the diagonal brace lugs or of the root radius of the clevis of the diagonal brace; in accordance with Table II of Figure 1 of Revision 7 of the alert service bulletin; at the time specified in paragraph (f)(1) or (f)(2) of this AD, whichever occurs later. Repeat the inspections thereafter at intervals not to exceed 1,000 flight cycles. Accomplishment of the applicable inspections constitutes terminating action for the repetitive inspection requirements of paragraph (b) of this AD. For airplanes on which any migrated or rotated bushing was detected during any inspection required by paragraph (b) of this AD, but on which the rework required by paragraph (c) of this AD has not been accomplished, accomplishment of the inspections required by paragraph (f) of this AD constitutes terminating action only for the repetitive inspection requirements of paragraph (d)(1) of this AD. However, rework of the diagonal brace lug in accordance with paragraph (d)(1) of this AD is still required within 15 or 18 months, as applicable, after the initial detection of the migrated or rotated bushing; repetitive detailed visual inspections are required within 9 months after accomplishment of the resealing or application of corrosion-inhibiting compound; and, if corrosion-inhibiting compound was applied in lieu of resealing the bushings in accordance with paragraph (d)(1) of this AD, reapplication of the corrosion-inhibiting compound is required at intervals not to exceed 9 months. \n\n\t\t(1) Inspect prior to the accumulation of 9,000 total flight cycles; or within 9,000 flight cycles after rework of the diagonal brace lug in accordance with Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, or Revision 7, or Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997. Or \n\n\t\t(2) Inspect within 60 days after the effective date of this AD. \n\n\t(g) If any migrated or rotated bushing is detected during any of the inspections required by paragraph (e) or (f) of this AD, prior to further flight, rework the diagonal brace lug, in accordance with Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, or Revision 7, dated November 20, 1998; or Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997; except as provided in paragraph (h) of this AD. Thereafter, repeat the detailed visual, HFEC, and ultrasonic inspections required by paragraph (e) of this AD within 5,000 flight cycles, and repeat the detailed visual, HFEC, and ultrasonic inspections required by paragraph (f) of this AD within 9,000 flight cycles, as applicable. If the lug bore diameter is not within the rework limits, or if any cracking of the root radius of the clevis is detected, prior to further flight, replace the diagonal brace with a new diagonal brace or repair it, in accordance with a method approved by the Manager, Seattle ACO, or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company DER who has been authorized by the Manager, Seattle ACO, to make such findings. \n\n\t(h) In lieu of accomplishing the requirements of paragraph (g) of this AD, perform ultrasonic and HFEC inspections to detect cracking or corrosion of the diagonal brace lug, in accordance with Boeing Alert Service Bulletin 747-54A2126, Revision 7, dated November 20, 1998. \n\t\t(1) If no cracking or corrosion is detected during the inspections required by paragraph (h) of this AD, prior to further flight, reseal the bushings or apply corrosion-inhibiting compound in accordance with the alert service bulletin, and accomplish the actions specified in paragraphs (h)(1)(i) and (h)(1)(ii) of this AD at the times specified in those paragraphs. If corrosion-inhibiting compound is applied, repeat the application at intervals not to exceed 9 months, in accordance with the alert service bulletin, until the actions required by paragraph (h)(1)(ii) of this AD have been accomplished. \n\n\t\t\t(i) Thereafter, repeat the detailed visual, HFEC, and ultrasonic inspections required by paragraphs (e) and (f) of this AD, as applicable, at intervals not to exceed those specified in Table 1 and Table II ofFigure 1 of the alert service bulletin, as applicable; except that the detailed visual inspection is required within 9 months after the resealing of the bushing or the application of corrosion-inhibiting compound. Accomplishment of such repetitive inspections terminates the repetitive inspection requirement of paragraph (d) of this AD. \n\t\t\t(ii) Within 15 or 18 months (as applicable in accordance with the alert service bulletin) since the initial detection of the migrated or rotated bushing required by paragraph (e) or (f) of this AD, rework the diagonal brace lug in accordance with Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, or Revision 7, dated November 20, 1998; or Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997. Thereafter, repeat the detailed visual, HFEC, and ultrasonic inspections required by paragraph (e) of this AD within 5,000 flight cycles and repeat the detailed visual, HFEC, and ultrasonic inspections required by paragraph (f) of this AD within 9,000 landings, as applicable. If the lug bore diameter is not within the rework limits, or if any cracking of the root radius of the clevis is detected, prior to further flight, replace the diagonal brace with a new diagonal brace or repair it, in accordance with a method approved by the Manager, Seattle ACO; or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company DER who has been authorized by the Manager, Seattle ACO, to make such findings. \n\n\t\t(2) If any cracking or corrosion is detected during the inspection required by paragraph (h) of this AD, prior to further flight, rework the diagonal brace lug in accordance with Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, or Revision 7, dated November 20, 1998; or Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997. Thereafter, repeat the detailed visual, HFEC, and ultrasonic inspections required by paragraph (e) of this AD within 5,000 landings and repeat the detailed visual, HFEC, and ultrasonic inspections required by paragraph (f) of this AD within 9,000 landings, as applicable. If the lug bore diameter is not within the rework limits, or if any cracking of the root radius of the clevis is detected, prior to further flight, replace the diagonal brace with a new diagonal brace or repair it, in accordance with a method approved by the Manager, Seattle ACO, or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company DER who has been authorized by the Manager, Seattle ACO, to make such findings. \n\n\t(i) If any cracking or corrosion is detected during any of the inspections required by paragraph (a), (b), (e), or (f) of this AD, prior to further flight, rework the diagonal brace lug in accordance with Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, or Revision 7, dated November 20, 1998; or Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997. Thereafter, repeat the detailed visual, HFEC, and ultrasonic inspections required by paragraph (e) of this AD within 5,000 landings and/or repeat the detailed visual, HFEC, and ultrasonic inspections required by paragraph (f) of this AD within 9,000 landings, as applicable. If the lug bore diameter is not within the rework limits, or if any cracking of the root radius of the clevis is detected, prior to further flight, replace the diagonal brace or repair it, in accordance with a method approved by the Manager, Seattle ACO, or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company DER who has been authorized by the Manager, Seattle ACO, to make such findings. \n\n\t(j) Accomplishment of a strut/wing modification in accordance with AD 95-10-16, amendment 39-9233; AD 95-13-05, amendment 39-9285; or AD 95-13-07, amendment 39-9287; as applicable; constitutes terminating action for the repetitive inspection requirements of this AD. \n\n\t(k) If Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, or Revision 7, dated November 20, 1998; or Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997; specifies that corrective actions may be accomplished in accordance with an operator's "equivalent procedure": The inspection and rework must be accomplished in accordance with the procedures or the chapter of the Boeing manuals specified in the service bulletin. \n\n\t(l) (1) An 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\t\t(2) Alternative methods of compliance, approved previously in accordance with AD 97-19-08, amendment 39-10128, are approvedas alternative methods of compliance with this AD. \n\n\t\t(3) Alternative methods of compliance, approved previously in accordance with AD 95-10-16, amendment 39-9233, are not considered to be approved as alternative methods of compliance with this AD. \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(m) Special 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(n) Except as provided by paragraphs (a)(2), (c), (d)(1), (d)(1)(ii), (d)(2), (g), (h)(1)(ii), (h)(2), (h)(2)(i), and (k) of this AD, the inspections, rework, and reseal shall be done in accordance with Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997; Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997; or Boeing Alert Service Bulletin 747-54A2126, Revision 7, dated November 20, 1998. \n\n\t\t(1) The incorporation by reference of Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, was approved previously by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51, as of September 29, 1997 (62 FR 47927, September 12, 1997). \n\n\t\t(2) The incorporation by reference of Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997; and Boeing Alert Service Bulletin 747-54A2126, Revision 7, dated November 20, 1998; is 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. \n\n\t(3) 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(o) This amendment becomes effective on January 15, 1999.

On September 5, 1997, the FAA issued AD 97-19-08, amendment 39-10128 (62 FR 47927, September 12, 1997), applicable to certain Boeing Model 747 series airplanes, to require repetitive detailed visual and ultrasonic inspections to detect cracking, corrosion, and migrated or rotated bushings of the diagonal brace lugs of the engine strut, and rework of the diagonal brace lugs, if necessary. In lieu of accomplishing the rework prior to further flight in certain cases where no cracking or corrosion is detected, that AD provides an option to defer the rework for a short period of time by resealing the bushing and accomplishing repetitive inspections. That AD also provides for an optional modification of the strut/wing, which would constitute terminating action for the repetitive inspection requirements. That action was prompted by reports of fatigue cracking in the diagonal brace lug. The actions required by that AD are intended to prevent such fatigue cracking, which could result in failure of the strut and consequent separation of the engine from the airplane. \n\nActions Since Issuance of Previous Rule \n\n\tSince the issuance of that AD, the FAA has received several reports indicating that additional cracking of the diagonal brace lugs has been detected on the affected airplanes. On several airplanes, cracks were found in the area of the lug common to the long axis of the diagonal brace. An ultrasonic inspection of that area was not required by AD 97-19-08. Therefore, cracking in the area of the lug common to the long axis of the diagonal brace may have gone undetected. Cracking was also detected in the root radius of the aft clevis of the diagonal brace. That area was not subject to inspections in accordance with AD 97-19-08. \n\n\tOn other airplanes, during repetitive inspections performed in accordance with AD 97-19-08, cracking of the diagonal brace lugs was detected during inspections performed earlier than the scheduled repetitive interval. Those airplanes had accumulated between 213 and 267 flight cycles since the previous inspection of the diagonal brace lugs. \n\nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved Boeing Service Bulletin 747-54A2126, Revision 6, dated August 28, 1997. That service bulletin is substantially similar to Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997 (which was referenced as the appropriate source of service information in AD 97-19-08). However, Boeing Service Bulletin 747-54A2126, Revision 6, clarifies the inspection method and intervals for the forward and aft diagonal brace lugs, and updates the effectivity listing of the service bulletin to reflect changes in airplane operators but adds no new airplanes. \n\n\tThe FAA also has reviewed and approved Boeing Alert Service Bulletin 747-54A2126, Revision 7, dated November 20, 1998. Revision 7 of the alert service bulletin was issued subsequent to the findings of new cracking, and describes procedures for a repetitive ultrasonic inspection that are substantially similar to those described in Revision 5 of the alert service bulletin and in Boeing Service Bulletin 747-54A2126, Revision 6. Revision 7 also describes procedures for rework of the diagonal brace lug; and an option to defer the rework, in cases where no cracking or corrosion is found, by resealing the bushing or applying a corrosion-inhibiting compound, and performing repetitive inspections. Those procedures are substantially similar to the procedures described in Revision 5 of the alert service bulletin and in Boeing Service Bulletin 747-54A2126, Revision 6. However, Revision 7 also describes procedures for a detailed visual inspection, for all airplanes, to detect cracks, corrosion, or other damage of the diagonal brace lug, as well as of the root radius of the clevis of the inboard and outboard diagonal braces. Revision 7 also describes procedures for repetitive high frequency eddy current inspections, for certain airplanes, to detect cracking or corrosion of the diagonal brace lugs. Revision 7 also specifies, for certain airplanes, revised repetitive inspection intervals. \n\nOther Relevant Rulemaking \n\n\tThe FAA previously has issued AD 95-10-16, amendment 39-9233 (60 FR 27008, May 22, 1995), applicable to Boeing Model 747 series airplanes equipped with Pratt & Whitney Model JT9D series engines (excluding Model JT9D-70 engines); AD 95-13-05, amendment 39-9285 (60 FR 33333, June 28, 1995), applicable to Boeing Model 747 series airplanes equipped with Rolls Royce Model RB211 series engines; and AD 95-13-07, amendment 39-9287 (60 FR 33336, June 28, 1995), applicable to Boeing Model 747 series airplanes equipped with General Electric Model CF6-45 or -50 series engines, or Pratt & Whitney Model JT9D-70 series engines. Those AD's require accomplishment of certain modifications of the nacelle strut/wing structure, which constitutes terminating action for the repetitive inspection requirements of this AD. \n\nExplanation of Requirements of Rule \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other airplanes of this same type design, this AD supersedes AD 97-19-08 to continue to require repetitive inspections to detect discrepancies of the diagonal brace lugs of the engine strut, and rework of the diagonal brace lugs, if necessary. This AD also continues to provide an option to defer the rework by accomplishing repetitive inspections and resealing the bushing. This AD also continues to provide for an optional terminating action for the repetitive inspection requirements. \n\n\tThis AD adds new repetitive inspections to detect discrepancies of the root radius of the clevis of the diagonal brace of the engine strut. For certain airplanes, this AD also adds new repetitive inspections to detect discrepancies of the diagonal brace lugs of the engine strut and requires that certain previously required repetitive inspections be accomplished at reduced intervals. The actions are required to be accomplished in accordance with the service bulletin or alert service bulletin described previously, except as discussed below. \n\nExplanation of Addition to Compliance Options \n\n\tAD 97-19-08 provides an option--in cases where a migrated or rotated bushing, but no cracking or corrosion, is detected--to defer the rework of the diagonal brace lugs by accomplishing repetitive inspections and resealing the bushing. However, Boeing Alert Service Bulletin 747-54A2126, Revision 5, specified that the rework could be deferred by accomplishing repetitive inspections and either resealing the bushing or applying a corrosion-inhibiting compound (and repeating the application of such compound at intervals not to exceed 9 months). The FAA finds that the option for application of a corrosion-inhibiting compound was inadvertently omitted from paragraph (d)(1) of AD 97-19-08. \nTherefore, paragraph (d)(1) of this AD, which restates the requirements of paragraph (d)(1) of AD 97-19-08, has been amended to read, ". . . reseal the bushings or apply corrosion-inhibiting compound . . . ." Related to this change, paragraph (d)(1) also specifies, "If corrosion-inhibiting compound is applied, repeat the application at intervals not to exceed 9 months . . . ." \n\nDifferences Between the Alert Service Bulletin and This AD \n\n\tOperators should note that Boeing Alert Service Bulletin 747-54A2126, Revision 7, specifies that the initial inspection threshold may be increased for diagonal braces that have been reworked in accordance with Boeing Service Bulletin 747-54-2126, dated June 16, 1988; Revision 1, dated August 25, 1988; Revision 2, dated April 27, 1989; Revision 3, dated October 19, 1989; or Revision 4, dated January 31, 1991. This AD, however, does not provide for such an increase in initial inspection thresholds for diagonal braces that have been reworked. \n\n\tThe FAA has determined that the compliance times for the initial inspection as specified in Tables 1 and II of Figure 1 of the alert service bulletin represent an appropriate interval of time allowable, such that the inspections do not pose an undue burden upon operators, and an acceptable level of safety of the transport airplane fleet can be maintained. In making this determination, the FAA has considered the manufacturer's recommendations as well as the safety implications of discrepancies of the diagonal brace lugs of the engine strut. However, under the provisions of paragraph (l)(1) of this AD, the FAA may approve requests for adjustment of the initial inspection threshold for diagonal braces that have been reworked in accordance with Boeing Service Bulletin 747-54-2126, original issue, Revision 1, Revision 2, Revision 3, or Revision 4. \n\n\tOperators also should note that, although the service bulletins specify that the manufacturer may be contacted for disposition of certain repair conditions, this AD requires the repair of those conditions to be accomplished in accordance with a method approved by the FAA, or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the FAA to make such findings. \n\n\tOperators also should note that Boeing Alert Service Bulletin 747-54A2126, Revision 5, dated June 26, 1997, and Revision 7, dated November 20, 1998; and Boeing Service Bulletin 747-54A2126, Revision 6; specify that certain corrective actions may be accomplished in accordance with "an operator's equivalent procedure." However, this AD requires that all inspection and rework procedures be accomplished in accordance with the procedures specified in the service bulletin. An "operator's equivalent procedure" for inspecting or reworking the diagonal brace may be used only if approved as an alternative method of compliance in accordance with paragraph (l)(1) of this AD. \n\nDeterminationof 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-327-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. \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. \n\n§ 39.13 (Amended) \n\n\t2. Section 39.13 is amended by removing amendment 39-10128 (62 FR 47927, September 12, 1997), and by adding a new airworthiness directive (AD), amendment 39-10976, to read as follows: