Airworthiness Directives; Boeing Model 747 Series Airplanes

Comments Invited

Interested persons are invited to participate in the making of the proposed 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 above. All communications received on or before the closing date for comments, specified above, will be considered before taking action on the proposed rule. The proposals contained in this notice may be changed in light of the comments received. Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the proposed 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 summarizing each FAA-public contact concerned with the substance of this proposal will be filed in the Rules Docket. Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this notice must submit a self-addressed, stamped postcard on which the following statement is made: ``Comments to Docket Number 98-NM-144-AD.'' The postcard will be date stamped and returned to the commenter.

Availability of NPRM's

Any person may obtain a copy of this NPRM by submitting a request to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 98-NM-144-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

The FAA has received reports from three operators indicating findings of six cracked or broken spring beam support fittings on the outboard struts of Model 747 series airplanes. Four of the cracked or broken support fittings were found on strut number 1 (left outboard strut), and two others were found on strut number 4 (right outboard strut). An operator of a Model 747-200 combi airplane that had accumulated 76,372 total flight hours and 14,501 total flight cycles reported finding a 5-inch crack in the inboard skin panel during a preflight check on the number 1 strut, and further investigation revealed a fractured support fitting on the inboard side of that strut. An operator of a Model 747-200F airplane equipped with General Electric CF6-50 series engines, which had accumulated 71,609 total flight hours and 14,808 total flight cycles, reported findings of a severed support fitting on the number 1 strut. Another operator of a Model 747-200F airplane equipped with Pratt & Whitney JT9D-70 series engines reported findings of two broken support fittings, one on the number 1 strut and one on the number 4 strut. A report indicated that, during a heavy maintenance preliminary check, a misaligned stripe on the outboard nacelle strut was found. Further investigation revealed a broken spring beam on the outboard side of the number 4 strut and a broken support fitting. This airplane had accumulated 72,426 total flight hours and 18,142 total flight cycles. An inspection of the remaining fleet of similar airplanes revealed findings of two fractured support fittings on an airplane that had accumulated 66,035 total flight hours and 16,709 total flight cycles. All of these operators reported findings of cracked or severed spring beam support fittings located on the inboard side of the strut and attached to the strut skin. These conditions, if not corrected, could cause fatigue cracking of the strut skin and spring beam support fittings on the outboard nacelle struts, which could result in failure of the outboard nacelle struts and consequent separation of the engine.

Other Relevant Rulemaking

The FAA has previously issued AD 95-13-07, amendment 39-9287 (60 FR 33336, June 28, 1995), which currently requires modification of the nacelle strut and wing structure, inspections and checks to detect discrepancies, and correction of discrepancies. The corrective action specified by that AD included a modification to improve the damage tolerance capability and durability of the strut-to-wing attachments, reduce reliance on non-routine inspections of those attachments, and prevent failure of the strut and consequent separation of the engine. Although the accomplishment of the modification required by that AD constitutes terminating action for the requirements of that AD, this proposed AD specifies that same modification as an optional terminating action.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Alert Service Bulletin 747-

54A2172, dated February 23, 1995, and Boeing Service Bulletin 747- 54A2172, Revision 1, dated January 4, 1996, which describe similar procedures for detecting cracks of the strut skin and spring beam support fittings, or detecting cracked or loose fasteners of the support fittings; and corrective actions, if necessary. The initial inspections differ from the repetitive inspections. The initial inspections include a visual inspection of the four spring beam support fittings, a detailed visual inspection of the support fitting at the fasteners using a borescope, a visual inspection of the fasteners, and a detailed visual inspection of the strut skin. The repetitive inspections include an inspection of the support fitting at fasteners through the horizontal flange, an inspection of the fasteners through the vertical flange for loose collars, an external visual inspection for loose fastener heads, and a detailed visual inspection of the strut skin. The terminating action in both service bulletins specifies an open- hole high frequency eddy current (HFEC) inspection and, if no cracks are found, rework of the fastener holes and installation of new fasteners. For airplanes on which any cracks are found during the HFEC inspection, Part III of the Accomplishment Instructions of the Boeing alert service bulletin specifies contacting the manufacturer for repair instructions. However, for those same airplanes, Revision 1 of the Boeing service bulletin adds a new section to the Accomplishment Instructions (``Part IV. Replacement''), which specifies procedures for replacing any cracked spring beam support fitting with a new support fitting. Accomplishment of this replacement action would eliminate the need for the repetitive inspections of that new support fitting.

Explanation of Requirements of Proposed Rule

Since an unsafe condition has been identified that is likely to exist or develop on other Boeing Model 747 series airplanes of this same type design, the proposed AD would require accomplishment of the actions specified by the service bulletins described previously, except as discussed below. The proposed AD also provides for several optional terminating actions. If no cracks are found, rework of the fastener holes and installation of new fasteners would constitute terminating action for the repetitive inspection requirements of this AD. If cracks are found during an open-hole HFEC inspection, replacement of the spring beam support fittings with new fittings constitutes optional terminating action for the repetitive inspection requirements of this AD.

Differences Between Proposed Rule and Service Information

Operators should note the following differences between the proposed rule and the service information: Boeing Alert Service Bulletin 747-54A2172, dated February 23, 1995, and Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996, provide procedures for terminating actions for the repetitive inspections. However, this proposed AD specifies those actions as optional terminating actions since the FAA has previously issued AD 95- 13-07, which requires a terminating modification that is considered acceptable for compliance with the optional terminating action specified by this AD. Although the Boeing alert service bulletin specifies that the manufacturer may be contacted for the disposition of certain repair conditions, this proposal would require that the repair of those conditions be accomplished in accordance with a method approved by the FAA.

Cost Impact

There are approximately 145 airplanes of the affected design in the worldwide fleet. The FAA estimates that 9 airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately 16 work hours per airplane to accomplish the proposed inspection, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be $8,640, or $960 per airplane, per inspection cycle. The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. Should an operator elect to accomplish the fastener hole inspection and modification, it would take approximately 20 work hours (excluding removal of the strut and spring beam) to accomplish it, at an average labor rate of $60 per hour. Based on these figures, the cost impact of this optional terminating action is estimated to be $1,200 per strut. Should an operator elect to accomplish the replacement of the spring beam support fittings with new support fittings, it would take approximately 108 work hours (excluding removal of the strut and spring beam) to accomplish it, at an average labor rate of $60 per hour. Based on these figures, the cost impact of this optional terminating action is estimated to be $6,480 per support fitting.

Regulatory Impact

The regulations proposed herein would 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 proposal would not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. For the reasons discussed above, I certify that this proposed regulation (1) is not a ``significant regulatory action'' under Executive Order 12866; (2) is not a ``significant rule'' under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) if promulgated, will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A copy of the draft regulatory evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting the Rules Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new airworthiness directive:

BOEING: Docket 98-NM-144-AD.

Applicability: Model 747 series airplanes, line numbers 202 through 886 inclusive, equipped with General Electric Model CF6-45/ 50 and Pratt & Whitney Model JT9D-70 series engines; on which the strut/wing modification has not been accomplished in accordance with AD 95-13-07, amendment 39-9287; certificated in any category.

Note 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 (h) 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.

Compliance: Required as indicated, unless accomplished previously. To detect and correct fatigue cracking of the strut skin and spring beam support fittings on the outboard nacelle struts, and cracked or loose fasteners of the support fittings, which could result in failure of the outboard nacelle struts and consequent separation of the engine, accomplish the following: (a) Prior to the accumulation of 13,000 total flight cycles, or within 6 months after the effective date of this AD, whichever occurs later, perform a detailed visual inspection of the outboard nacelle struts, as specified by paragraphs (a)(1), (a)(2), (a)(3), and (a)(4) of this AD, in accordance with Boeing Alert Service Bulletin 747-54A2172, dated February 23, 1995, or Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996. (1) Inspect the spring beam support fittings to detect cracks of the support fittings. (2) Inspect the spring beam support fittings at the fasteners, using a borescope to detect cracks of the support fittings. (3) Inspect the fasteners of the outer spring beam support fittings to detect cracked or loose fasteners. (4) Inspect the strut skin to detect cracks. (b) If no discrepancy is found during any inspection required by paragraph (a) of this AD, perform detailed visual inspections of the outboard nacelle struts to detect any discrepancies specified in paragraphs (b)(1), (b)(2), (b)(3), and (b)(4) of this AD, in accordance with Boeing Alert Service Bulletin 747-54A2172, dated February 23, 1995; or Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996. Perform the inspection at the times specified in paragraph (c) or (d) of this AD, as applicable. (1) Perform a detailed visual inspection, using a borescope, of only the outer spring beam support fittings at the fasteners through the horizontal flange to detect cracks of the support fittings. (2) Perform a detailed visual inspection, using a borescope, of the fasteners through the vertical flange of only the outer spring beam support fittings to detect loose collars. (3) Perform an external detailed visual inspection of only the outer spring beam support fittings to detect cracked or loose fastener heads. (4) Perform a detailed visual inspection of the strut skin to detect cracks. (c) For Model 747-SR series airplanes equipped with General Electric Model CF6-45 series engines, on which no discrepancy is found during any inspection required by paragraph (a) of this AD: Perform the inspection required by paragraph (b) of this AD within 1,600 flight cycles following the accomplishment of the inspection required by paragraph (a) of this AD; and thereafter at intervals not to exceed 1,600 flight cycles until accomplishment of the optional terminating action specified in paragraph (g) of this AD. (d) For Model 747 series airplanes other than those identified in paragraph (c) of this AD, on which no discrepancy is found during any inspection required by paragraph (a) of this AD: Perform the inspection required by paragraph (b) of this AD within 1,000 flight cycles following the accomplishment of the inspection required by paragraph (a) of this AD; and thereafter at intervals not to exceed 1,000 flight cycles until accomplishment of the optional terminating action specified in paragraph (g) of this AD. (e) If any cracking is found in the spring beam support fittings during any inspection required by this AD, prior to further flight, replace the support fitting with a new support fitting, in accordance with the Accomplishment Instructions in Part IV. of Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996. Accomplishment of this replacement constitutes terminating action for the repetitive inspection requirements of this AD for only the new support fitting. Continue the repetitive inspections required by paragraph (b) of this AD for the other support fitting locations until accomplishment of the terminating action specified by paragraph (g)(1) or (g)(2) of this AD, as applicable. (f) If any crack is found on the strut skin, or if any cracked or loose fastener or collar is found during any inspection required by this AD, prior to further flight, repair 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 who has been authorized by the Manager, Seattle ACO, to make such findings. (g) Accomplishment of an open-hole high frequency eddy current (HFEC) inspection, in accordance with Boeing Alert Service Bulletin 747-54A2172, dated February 23, 1995, or Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996; and either paragraph (g)(1) or (g)(2) of this AD, as applicable; constitutes terminating action for the requirements of this AD. (1) If no discrepancy is found during the HFEC inspection, prior to further flight, rework the fastener holes and install new fasteners, in accordance with Figures 6 and 7 of Boeing Alert Service Bulletin 747-54A2172, dated February 23, 1995, or Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996. (2) If any cracking is found during the HFEC inspection, prior to further flight, replace any cracked spring beam support fitting with a new support fitting, in accordance with Part IV. of the Accomplishment Instructions specified by Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996. (h) 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, FAA. 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.

Note 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

(i) 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.

Issued in Renton, Washington, on November 18, 1998. Darrell M. Pederson, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service. [FR Doc. 98-31327 Filed 11-23-98; 8:45 am] BILLING CODE 4910-13-U