Airworthiness Directives; Boeing Model 747-100, -200, and 747SP Series Airplanes

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Final rule.

SUMMARY:

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747-100, -200, and 747SP series airplanes, that requires repetitive detailed visual and ultrasonic inspections to detect missing, damaged, or broken taperlock bolts in the diagonal brace underwing fittings; and corrective actions, if necessary. This AD also requires eventual replacement of the aft 10 taperlock bolts with new bolts, which constitutes terminating action for the repetitive inspections. This amendment is prompted by reports of damaged, broken, and corroded taperlock bolts of the diagonal brace underwing fittings on the outboard strut due to stress corrosion cracking. The actions specified by this AD are intended to prevent loss of the underwing fitting load path due to missing, damaged, or broken taperlock bolts, which could result in separation of the engine and strut from the airplane.

DATES:

Effective March 28, 2000.

The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of March 28, 2000.

ADDRESSES:

The 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 Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

FOR FURTHER INFORMATION CONTACT:

Tamara L. Anderson, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2771; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION:

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain Boeing Model 747-100, -200, and 747SP series airplanes was published in the Federal Register on August 31, 1999 (64 FR 47440). That action proposed to require repetitive detailed visual and ultrasonic inspections to detect missing, damaged, or broken taperlock bolts in the diagonal brace underwing fittings; and corrective actions, if necessary. That action also proposed to require eventual replacement of the aft 10 taperlock bolts with new bolts as terminating action for the repetitive inspections.

Comments

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

Support for the Proposal

One commenter supports the proposed rule.

Request to Reference Other Terminating Action

One commenter requests that the FAA revise the notice of proposed rulemaking (NPRM) to reference accomplishment of Boeing Service Bulletin 747-57-2288 as terminating action for the repetitive inspection requirements proposed in the NPRM. The commenter states that accomplishment of the replacement of the diagonal brace underwing fitting in accordance with Figures 5 through 9 of that service bulletin, or the clearance adjustment in accordance with Figure 10 of that service bulletin, includes replacement of the same taperlock bolts with new bolts as described in the NPRM and in Boeing Alert Service Bulletin 747-57A2308, dated August 6, 1998 (which was referenced as the appropriate source of service information for the actions proposed in the NPRM). The commenter states that if the taperlocks that are the subject of this AD have already been replaced with the same new bolts that are specified in this AD, the operator should not be required to do the inspections proposed in the NPRM or apply for approval of an alternative method of compliance. The commenter states that if its request is granted and incorporated in the final rule, operators and the FAA will not have to process as many applications for alternative methods of compliance.

The FAA concurs with the commenter's request. The FAA finds that accomplishment of the replacement of the diagonal brace underwing fitting or the clearance adjustment described in Boeing Service Bulletin 747-57-2288, Revision 1, dated June 26, 1997, is acceptable for compliance with the requirements of paragraph (d) of this AD. Accordingly, a new NOTE 3 has been added to this final rule. However, the FAA finds that accomplishment of such replacement or clearance adjustment in accordance with the original issue of Boeing Service Bulletin 747-57-2288, dated September 15, 1994, is not acceptable for compliance with paragraph (d) of this AD, because that service bulletin does not specify to replace the taperlock bolts that are subject to this AD.

Request to Clarify “Spares” Paragraph

One commenter requests that the FAA revise paragraph (e) of the NPRM to change the words “on any airplane” to “on any Boeing 747 airplane that is listed in the effectivity of [Boeing Service Bulletin] 747-57A2308.” The commenter states that an operator was confused about the meaning of the paragraph as it is phrased in the NPRM.

The FAA concurs with the intent of the commenter's request. The FAA acknowledges that the language used in the NPRM may confuse some operators. Therefore, paragraph (e) of this final rule has been revised to state that, “. . . no person shall install a bolt, part number BACB30PE( ) * ( ), or any other bolt made of 4340, 8740, or PH13-8 Mo steel, in the locations specified in this AD, on any airplane listed in the applicability of this AD.”

Request to Revise Estimated Cost of Terminating Action

One commenter requests that the FAA revise the estimated cost of the terminating action, as quoted in the proposed rule. The commenter points out that the number of work hours for accomplishment of the terminating action stated in the NPRM (i.e., 8 work hours) is inconsistent with the estimate in Boeing Alert Service Bulletin 747-57A2308. The commenter estimates that 248 to 306 work hours per airplane is necessary to accomplish the proposed replacement of taperlock bolts.

The FAA partially concurs with the commenter's request. The FAA does not concur with the commenter's estimate of 248 to 306 work hours, because that estimate includes time to gain access and close up. The cost analysis in AD rulemaking actions typically does not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. Because such incidental costs may vary significantly from operator to operator, they are almost impossible to calculate. However, the FAA finds that the number of work hours necessary for accomplishment of the terminating action is underestimated in the NPRM. The FAA estimates that the terminating action will take 68 work hours for airplanes in Groups 1, 2, and 5, and 125 work hours for airplanes in Groups 3 and 4. (These estimates coincide with Boeing's estimate for the number of work hours necessary to accomplish the terminating action if it is accomplished concurrently with other strut modifications.) The FAA has revised the cost impact information in this final rule accordingly.

Request To Delete Terminating Action Requirement

One commenter requests that the FAA revise the NPRM to delete the requirement to replace the subject taperlocks within 48 months after the effective date of this AD. The commenter states that the diagonal-brace-to-wing attachment can carry ultimate load with a certain number of failed taperlocks. The commenter asserts that the visual and ultrasonic inspections that are proposed in the NPRM will reliably detect bolt fractures before multiple fractures occur, and will ensure that the outboard engines and struts will not separate from the airplane. Furthermore, the commenter states that removing the subject taperlocks is a difficult and time-consuming procedure, necessitating costs and downtime not commensurate with the degree of enhanced flight safety.

The FAA does not concur with the commenter's request. As stated in the “Differences Between Proposed Rule and Service Bulletin” section of the NPRM, the FAA has determined that long-term inspections may not provide the degree of safety assurance necessary for the transport airplane fleet. The commenter supplied no data (such as the crack growth rate after inspection, to ensure that the inspection interval is adequate for timely detection of cracking) to support its statement that inspections will reliably detect bolt fractures before multiple fractures occur. The FAA finds that no change to the final rule is necessary in this regard.

Request To Allow Installation of Cadmium-Plated Taperlock Bolts

One commenter requests that the FAA revise paragraph (e) of the NPRM to state that taperlock bolts made of 4340, 8740, or PH13-8 Mo steel with no coating or with aluminum coating may be installed. [Paragraph (e) of the NPRM states that no bolt made of 4340, 8740, or PH13-8 Mo steel—regardless of the type of coating—may be installed.] The commenter states that it has had no service problems with cadmium-plated 4340, 8740, or PH13-8 Mo steel taperlock bolts, and further states that such cadmium-plated 4340 and 8740 steel taperlock bolts are approved for use in the Boeing 747 Structural Repair Manual, which is approved by the FAA.

The FAA does not concur with the commenter's request to allow use of cadmium-plated steel taperlock bolts. The terminating action required by this AD requires installation of BACB30NX*K* bolts. The material that these bolts are made of is less susceptible to stress corrosion cracking than the bolts with cadmium plating that the commenter specifies. In addition, the FAA has determined that BACB30NX*K* bolts are not listed in Boeing 747 Structural Repair Manual, Chapter 51-30-03, Figure 1, Sheet 37. Therefore, cadmium-plated 4340 and 8740 steel taperlock bolts are not approved for use in place of the BACB30NX*K* bolts required by this AD. No change to the final rule is necessary in this regard.

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 with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.

Cost Impact

There are approximately 274 Model 747-100, -200, and 747SP series airplanes of the affected design in the worldwide fleet. The FAA estimates that 122 airplanes of U.S. registry will be affected by this AD.

It will take approximately 1 work hour per airplane to accomplish the required inspection, at the average labor rate of $60 per work hour. Based on these figures, the cost impact of the required inspection on U.S. operators is estimated to be $7,320, or $60 per airplane, per inspection cycle.

It will take approximately 68 work hours per airplane to accomplish the required terminating action for airplanes included in Groups 1, 2, and 5, as specified in the service bulletin. It will take approximately 125 work hours to accomplish the required terminating action for airplanes included in Groups 3 and 4, as specified in the service bulletin. The average labor rate is $60 per work hour. Required parts will cost approximately $8,008 per airplane. Based on these figures, the cost impact of the required terminating action on U.S. operators is estimated to be $12,088 per airplane, for airplanes in Groups 1, 2, and 5; and $15,508 per airplane, for airplanes in Groups 3 and 4.

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 a substantial direct effect 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, it is determined that this final rule does not have federalism implications under Executive Order 13132.

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.

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

2000-03-22 Boeing: Amendment 39-11582. Docket 98-NM-339-AD.

Applicability: Model 747-100, -200, and 747SP series airplanes; line numbers 1 through 567 inclusive; equipped with aluminum diagonal brace underwing fittings; 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 actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent loss of the underwing fitting load path due to missing, damaged, or broken taperlock bolts, which could result in separation of the engine and strut from the airplane, accomplish the following:

Repetitive Inspections

(a) Prior to the accumulation of 9,000 total flight cycles, or within 18 months after the effective date of this AD, whichever occurs later, accomplish the actions required by paragraphs (a)(1) and (a)(2) of this AD in accordance with Boeing Alert Service Bulletin 747-57A2308, dated August 6, 1998. Thereafter, repeat the inspections at intervals not to exceed 18 months until accomplishment of the actions specified in paragraph (d) of this AD.

(1) Perform a detailed visual inspection to detect missing taperlock bolts in the diagonal brace underwing fitting at the Number 1 and Number 4 pylons.

Note 2:

For the purposes of this AD, a detailed visual inspection is defined as: “An intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required.”

(2) Perform an ultrasonic inspection to detect damaged or broken taperlock bolts in the diagonal brace underwing fitting at the Number 1 and Number 4 pylons.

Corrective Actions

(b) If any missing, damaged, or broken taperlock bolt is detected during any inspection required by paragraph (a) of this AD, prior to further flight, perform the applicable corrective actions (i.e., inspection, drill/ream, and replacement) in accordance with Boeing Alert Service Bulletin 747-57A2308, dated August 6, 1998; except as provided in paragraph (c) of this AD. Replacement of any taperlock bolt with a new bolt in accordance with this paragraph constitutes terminating action for the repetitive inspections required by paragraph (a) of this AD for that bolt only.

(c) If any crack is detected during the inspection required by paragraph (b) of this AD and the damage to a bolt hole exceeds first oversize (for 0.5-inch bolts) or second oversize (for 0.4375-inch bolts); and the service bulletin specifies to contact Boeing for appropriate action: 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 a Boeing Company Designated Engineering Representative who has been authorized by the Manager, Seattle ACO, to make such findings. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the Manager's approval letter must specifically reference this AD.

Terminating Action

(d) Within 48 months after the effective date of this AD, accomplish the actions required by paragraphs (d)(1) and (d)(2) of this AD in accordance with Boeing Alert Service Bulletin 747-57A2308, dated August 6, 1998. Accomplishment of the actions specified in this paragraph constitutes terminating action for the repetitive inspection requirements of this AD.

(1) Prior to accomplishing the replacement required by paragraph (d)(2) of this AD, perform an open hole high frequency eddy current inspection to detect cracks at the bolt hole locations of the aft 10 taperlock bolts. If any cracking is detected, prior to further flight, perform applicable corrective actions in accordance with paragraph (c) of this AD.

(2) Replace the aft 10 taperlock bolts with new bolts in the diagonal brace underwing fitting at the Number 1 and Number 4 pylons.

Note 3:

Accomplishment of the replacement of the diagonal brace underwing fitting in accordance with Figures 5 through 9 of Boeing Service Bulletin 747-57-2288, Revision 1, dated June 26, 1997; or the clearance adjustment in accordance with Figures 10 through 14 of that service bulletin; is acceptable for compliance with the requirements of paragraph (d) of this AD.

Spares

(e) As of the effective date of this AD, no person shall install a bolt, part number BACB30PE() * (), or any other bolt made of 4340, 8740, or PH13-8 Mo steel, in the locations specified in this AD, on any airplane listed in the applicability of this AD.

Alternate Method of Compliance

(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 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.

Note 4:

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

Special Flight Permits

(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.

Incorporation by Reference

(h) Except as provided in paragraph (c) of this AD, the actions shall be done in accordance with Boeing Alert Service Bulletin 747-57A2308, dated August 6, 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.

(i) This amendment becomes effective on March 28, 2000.