# AD 98-21-17: Spring Beams on Outboard Struts - Type: Airworthiness directive - Status: Current - Products: Boeing 747-100 Series, 747-100B Series, 747-100B SUD Series, 747-200B Series, 747-200C Series, 747-200F Series, 747-300 Series, 747-400 Series, 747-400D Series, 747-400F Series, 747SP Series and 747SR Series - Effective: November 17, 1998 - Published: October 13, 1998, 63 FR 54569–54570 - Issued as: Final rule - Supersedes: [AD 94-25-01](https://openairdocs.org/ad/94-25-01) - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Large airplane - Amendment: 39-10826 - Docket: 97-NM-185-AD - Registered aircraft: 63 may be affected, by airframe or engine model (OpenAirDocs) - Official PDF: https://openairdocs.org/files/sha256/1e/13/1e13d4c1b139603cb70c004f18330da3cd30840baae4fcc67cb18b52a7494198 (from https://www.govinfo.gov/content/pkg/FR-1998-10-13/pdf/98-26966.pdf) - Federal Register: https://www.federalregister.gov/documents/1998/10/13/98-26966/airworthiness-directives-boeing-model-747-series-airplanes-equipped-with-pratt-and-whitney-model - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/B3DB0801B16A6ECB86256981006A0B79.0001 - DRS record last changed: May 30, 2024 - Page: https://openairdocs.org/ad/98-21-17 ## Summary This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that currently requires repetitive inspections to detect fatigue cracking of the spring beams on the outboard struts; replacement of cracked spring beams with new or serviceable spring beams; and follow-on actions. That action also provides an optional terminating action for the repetitive inspections. This amendment removes that optional terminating action, and requires a new terminating action. This amendment is prompted by the development of an improved process for manufacturing titanium spring beams that will eliminate the embedded porosity flaws in the existing spring beams from which fatigue cracking can originate. The actions specified by this AD are intended to prevent fatigue cracking of the spring beam, which could result in loss of an outboard strut. ## The airworthiness directive 98-21-17 BOEING: Amendment 39-10826. Docket 97-NM-185-AD. Supersedes AD 94-25-01, Amendment 39-9085. Applicability: Model 747 series airplanes, line numbers 202 through 396 inclusive, equipped with Pratt & Whitney Model JT9D-70 engines; certificated in any category. NOTE 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 (f) 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 actionsto address it. Compliance: Required as indicated, unless accomplished previously. To prevent fatigue cracking of the spring beam, which could result in loss of an outboard strut, accomplish the following: (a) Prior to the accumulation of 10,000 total flight cycles, or within 30 days after December 22, 1994 (the effective date of AD 94-25-01), whichever occurs later, perform a detailed visual inspection to detect fatigue cracking of the spring beams on the outboard struts, in accordance with Boeing Alert Service Bulletin 747-54A2171, dated October 31, 1994, or Revision 1, dated June 27, 1996. (Remove the gap covers and fairing access panels to perform this inspection.) (1) If no cracking is detected, repeat the visual inspection thereafter at intervals not to exceed 300 flight cycles until the requirements of paragraph (d) of this AD have been accomplished. (2) If any cracking is detected, prior to further flight, accomplish the replacement actions specified in paragraph (d) of this AD. NOTE 2: Accomplishment of the optional terminating action specified in paragraph (b) of AD 94-25-01 does not constitute terminating action for the requirements of this AD. (b) For airplanes that have accomplished terminating action in accordance with paragraph (b) of AD 94-25-01: Within 1,000 flight cycles after accomplishment of the terminating action specified by AD 94-25-01, or within 90 days after the effective date of this AD, whichever occurs later, perform a detailed visual inspection to detect fatigue cracking of the spring beams on the outboard struts, in accordance with Boeing Alert Service Bulletin 747-54A2171, dated October 31, 1994, or Revision 1, dated June 27, 1996. (1) If no cracking is detected, repeat the detailed visual inspection thereafter at intervals not to exceed 300 flight cycles until the requirements of paragraph (d) of this AD have been accomplished. (2) If any cracking is detected, prior to further flight, accomplish the replacement actions specified in paragraph (d) of this AD. (c) For airplanes that have accomplished installation of the Boeing-inspected spare titanium spring beams in accordance with Boeing Service Bulletin 747-54A2171, Revision 1, dated June 27, 1996: Within 3,000 flight cycles after accomplishment of the installation of the spare spring beams, or within 90 days after the effective date of this AD, whichever occurs later, perform a detailed visual inspection to detect fatigue cracking of the spring beams on the outboard struts, in accordance with Boeing Alert Service Bulletin 747-54A2171, dated October 31, 1994, or Revision 1, dated June 27, 1996. (1) If no cracking is detected, repeat the detailed visual inspection thereafter at intervals not to exceed 300 flight cycles until the requirements of paragraph (d) of this AD have been accomplished. (2) If any cracking is detected, prior to further flight, accomplish the replacement actions specified inparagraph (d) of this AD. (d) For all airplanes: Prior to the accumulation of 10,000 total flight cycles, or within 18 months after the effective date of this AD, whichever occurs later, replace the spring beams on the outboard struts with new, improved spring beams, in accordance with Boeing Service Bulletin 747-54-2177, dated June 27, 1996. Accomplishment of this replacement constitutes terminating action for the repetitive inspection requirements of this AD. (e) As of the effective date of this AD, no person shall install a spring beam assembly, part numbers 65B89175-5, -6, -9, -10, -13, -14, -19, and -20, on any airplane. (f) 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 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. NOTE 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. (g) 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. (h) The actions shall be done in accordance with Boeing Alert Service Bulletin 747-54A2171, dated October 31, 1994, or Boeing Alert Service Bulletin 747-54A2171, Revision 1, dated June 27, 1996; and Boeing Service Bulletin 747-54-2177, dated June 27, 1996. (1) The incorporation by reference of Boeing Alert Service Bulletin 747-54A2171, Revision 1, dated June 27, 1996, and Boeing Service Bulletin 747-54-2177, dated June 27, 1996, is approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and1 CFR part 51. (2) The incorporation by reference of Boeing Alert Service Bulletin 747-54A2171, dated October 31, 1994, was approved previously by the Director of the Federal register as of December 22, 1994 (59 FR 63003, December 7, 1994). (3) 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. (i) This amendment becomes effective on November 17, 1998. ## Rule preamble ### Supplementary information A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) by superseding AD 94-25-01, amendment 39-9085 (59 FR 63003, December 7, 1994), which is applicable to certain Boeing Model 747 series airplanes, was published in the Federal Register on July 7, 1998 (63 FR 36628). The action continues to require repetitive inspections to detect fatigue cracking of the spring beams on the outboard struts; replacement of cracked spring beams with new or serviceable spring beams; and follow-on actions. The action also proposed to remove the previously optional terminating action, and require a new terminating action. Comments Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the single comment received. The commenter supports the proposed rule. Conclusion After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed. Cost Impact There are approximately 7 airplanes of the affected design in the worldwide fleet. The FAA estimates that 5 airplanes of U.S. registry will be affected by this AD. The inspections that are currently required by AD 94-25-01, and retained in this AD, take approximately 40 work hours per airplane, per inspection cycle, to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the currently required inspections on U.S. operators is estimated to be $12,000, or $2,400 per airplane, per inspection cycle. The new replacement required by this AD will take approximately 376 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will cost approximately $105,000 per airplane. Based on these figures, the cost impact of the replacement required by this AD on U.S. operators is estimated to be $637,800, or $127,560 per airplane. The cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. Regulatory Impact The 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. For 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 of the 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." List of Subjects in 14 CFR Part 39 Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. Adoption of the Amendment Accordingly, 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: 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. § 39.13 (Amended) 2. Section 39.13 is amended by removing amendment 39-9085 (59 FR 63003, December 7, 1994), and by adding a new airworthiness directive (AD), amendment 39-10826, to read as follows: ## Affected data sheets (1) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS A20WE](https://openairdocs.org/tcds/A20WE): The Boeing Company; names 12 of 14 models: 747-100B Series, 747SP Series, 747-400D Series, 747-400F Series, 747-200B Series, 747-200F Series, 747-300 Series, 747-200C Series… ## Registered aircraft it may apply to (OpenAirDocs) Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment. - Aircraft: 63 (63 by airframe model, 0 by engine model) - Makers: Boeing 63 Models with the most aircraft: - [Boeing 747-446](https://openairdocs.org/model/boeing-747-446): 10 aircraft (airframe model) - [Boeing 747-422](https://openairdocs.org/model/boeing-747-422): 8 aircraft (airframe model) - [Boeing 747-412](https://openairdocs.org/model/boeing-747-412): 5 aircraft (airframe model) - [Boeing 747-400F](https://openairdocs.org/model/boeing-747-400f): 4 aircraft (airframe model) - [Boeing 747-409](https://openairdocs.org/model/boeing-747-409): 4 aircraft (airframe model) - [Boeing 747-481F](https://openairdocs.org/model/boeing-747-481f): 3 aircraft (airframe model) - [Boeing 747-409F](https://openairdocs.org/model/boeing-747-409f): 3 aircraft (airframe model) - [Boeing 747-481](https://openairdocs.org/model/boeing-747-481): 3 aircraft (airframe model) - [Boeing 747-428F](https://openairdocs.org/model/boeing-747-428f): 3 aircraft (airframe model) - [Boeing 747-123](https://openairdocs.org/model/boeing-747-123): 2 aircraft (airframe model) - [Boeing 747-251F](https://openairdocs.org/model/boeing-747-251f): 2 aircraft (airframe model) - [Boeing 747-443](https://openairdocs.org/model/boeing-747-443): 2 aircraft (airframe model) - [Boeing 747-438](https://openairdocs.org/model/boeing-747-438): 2 aircraft (airframe model) - [Boeing 747-428](https://openairdocs.org/model/boeing-747-428): 2 aircraft (airframe model) - [Boeing 747-257B](https://openairdocs.org/model/boeing-747-257b): 1 aircraft (airframe model) - [Boeing 747-283B](https://openairdocs.org/model/boeing-747-283b): 1 aircraft (airframe model) - [Boeing 747-121](https://openairdocs.org/model/boeing-747-121): 1 aircraft (airframe model) - [Boeing 747-131](https://openairdocs.org/model/boeing-747-131): 1 aircraft (airframe model) - [Boeing 747-128](https://openairdocs.org/model/boeing-747-128): 1 aircraft (airframe model) - [Boeing 747-273C](https://openairdocs.org/model/boeing-747-273c): 1 aircraft (airframe model) All 24 models: https://openairdocs.org/ad/98-21-17/models.md Every aircraft: https://openairdocs.org/ad/98-21-17/aircraft.md ## Related documents - [AD 94-25-01](https://openairdocs.org/ad/94-25-01) (historical): Outboard Strut · Boeing 747 Series (all). Effective Dec 22, 1994. Replaced by this AD - [Proposed rule 97-NM-185-AD](https://openairdocs.org/proposed/97-NM-185-AD): Notice of proposed rulemaking (NPRM), published Jul 7, 1998 Its text cites no advisory circulars or STCs. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.