00-8518. Airworthiness Directives; Boeing Model 767 Series Airplanes

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Final rule.

SUMMARY:

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 767 series airplanes, that currently requires repetitive inspections to detect cracking or damage of the forward and aft lugs of the diagonal brace of the nacelle strut, and follow-on actions, if necessary. That AD also provides optional terminating action for the repetitive inspections. This amendment requires accomplishment of the previously optional terminating action. This amendment is prompted by a report that a fractured diagonal brace lug was found during a routine maintenance inspection. The actions specified by this AD are intended to prevent cracking of the diagonal brace of the nacelle strut, which could result in failure of the diagonal brace, and consequent fatigue failure of a strut secondary load path and separation of the engine and strut.

DATES:

Effective May 15, 2000.

The incorporation by reference of Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998, was approved previously by the Director of the Federal Register as of April 12, 1999 (64 FR 14578, March 26, 1999).

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:

James G. Rehrl, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone [phone]; fax [phone].

SUPPLEMENTARY INFORMATION:

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) by superseding AD 99-07-06, amendment 39-11091 (64 FR 14578, March 26, 1999), which is applicable to certain Boeing Model 767 series airplanes, was published in the Federal Register on June 23, 1999 (64 FR 33437). The action proposed to supersede AD 99-07-06 to continue to require repetitive inspections to detect cracking or damage of the forward and aft lugs of the diagonal brace of the nacelle strut, and follow-on actions, if necessary. That action also proposed to require accomplishment of the previously optional 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 comments received.

Support for the Proposal

Two commenters support the proposed rule.

Requests To Revise Compliance Time

One commenter requests that the compliance time for the repetitive inspection intervals specified in paragraph (b)(1) of the proposed AD be extended. The commenter suggests that the inspection intervals should coincide with its current heavy maintenance program, which specifies that inspections be performed between 1,200 and 1,300 flight cycles. The commenter further states that to carry out the inspection at intervals not to exceed 1,000 flight cycles would be considered punitive action as it is prior to the normally scheduled maintenance.

The FAA does not concur with the commenter's request to extend the compliance time for accomplishment of the repetitive inspection intervals to between 1,200 and 1,300 flight cycles after the initial inspection. In developing an appropriate compliance time for the repetitive inspections, the FAA considered not only the degree of urgency associated with addressing cracking or damage of the forward and aft lugs of the diagonal brace of the nacelle strut, but other factors as well. Those factors include the recommendations of the manufacturer, and the practical aspect of accomplishing the repetitive inspections within an interval of time coinciding with normally scheduled maintenance for the majority of affected operators. Considering those factors, the FAA has determined that the compliance time of 1,000 flight cycles after the accomplishment of the initial inspection represents the maximum interval in which the affected airlines can continue to operate without compromising safety. In view of those factors, and the amount of time that has already elapsed since issuance of the notice of proposed rulemaking, the FAA has determined that further delay of these inspections is, in general, not appropriate. The FAA may, however, approve a request for an adjustment of the compliance time under the provisions of paragraph (f) of this final rule if data are submitted to substantiate that such an adjustment would provide an equivalent level of safety. No change to the final rule is necessary in this regard.

Another commenter requests that the compliance times for the replacement of the diagonal brace specified in paragraphs (d) and (e) of the proposed rule be changed to reflect the flight cycle threshold formula specified in the structural inspection program service bulletin, 767-54-0081, Figure 1, which is to be released soon. The commenter also notes that the threshold formula could be placed in an appendix to the proposal.

The FAA does not concur with the commenter's request. Boeing Service Bulletin 767-54-0081 states that the threshold formula may be used in lieu of the calendar threshold specified in the identified service bulletins. The formula in service bulletin 767-54-0081 was FAA-approved based on the fact that certain airplanes (e.g., those that have extended flights) would reach the 20-year calendar threshold long before they accumulated the flight cycle threshold of 37,500 total flight cycles specified in that service bulletin. The FAA notes that there is no comparable threshold in calendar time contained in this final rule for which the proposed threshold formula can be used as a substitute. The FAA considered many factors (as stated previously) before developing an appropriate compliance time for this AD, and the FAA has determined that the compliance time for the replacement required by paragraphs (d) and (e) of the final rule represents the maximum interval in which the affected airlines can continue to operate without compromising safety. Therefore, no change to the final rule is necessary.

Another commenter requests the compliance time in paragraph (b)(2) of the proposal be revised to read, “* * * diagonal brace has accumulated 24,000 flight cycles * * *” to agree with the alert service bulletin. The FAA does not concur. The alert service bulletin specifies that the initial inspection for Group 2 airplanes be performed prior to the accumulation of 24,000 flight cycles, or within 90 days after receipt of the service bulletin; and the repetitive inspections be performed at intervals not to exceed 3,000 flight cycles until the diagonal brace has accumulated 32,000 flight cycles. Therefore, the final rule agrees with the alert service bulletin and no change is necessary in this regard.

Request To Revise Paragraphs (a), (b), and (c) of the Proposed Rule

Three commenters request that the word “damage” be deleted from or clarified in paragraphs (a), (b), and (c) of the proposal.

The first commenter states that, if any damage is detected, even if it is minor and repairable, replacement of the diagonal brace is required, as specified in paragraph (c) of the proposal. The commenter further states that the alert service bulletin referenced in the proposal specifies an inspection to detect cracking of the diagonal brace lugs only, and does not specify inspecting for damage; therefore, the word “damage” should be deleted.

The second commenter states that if the words “or damage” are not removed, paragraphs (a), (b), and (c) of the proposal should specifically clarify what should be searched for (cracks, fracture) during the inspection. The same commenter requests the addition of a requirement in paragraph (c) of the proposal to specify that damage to the lug bores (including wear, cracks, or surface corrosion) be repaired in accordance with Part 2 of the Accomplishment Instructions of the alert service bulletin.

The third commenter states that the word “damage” is undefined in the proposed rule, and notes that the alert service bulletin specifies that cracks originated in the lug bore of the diagonal brace caused by bushing motion and subsequent fretting of the lug bore, indicating that the damage that caused the cracks was fretting of the lug bore. The commenter also notes that the detailed visual inspection required by paragraph (a) of the proposal does not inspect the lug bore; therefore, the fretting or “damage” will not be found. The commenter indicates that, without any damage limit guidelines, even very minor damage (tool marks, scratched paint) will make it necessary for operators to perform costly additional inspections. The commenter notes that the inspection should be limited to the unsafe condition that is caused by fretting of the lug bore, which can be found by crack indications.

The FAA does not concur with the commenters' requests concerning removal of the word “damage” as referenced in paragraphs (a), (b), and (c) of the final rule. The FAA has reviewed this issue and has determined that the inspection to detect cracks or damage as required by paragraphs (a) and (b) of the final rule, is necessary. Certain types of damage, if detected, specifically fretting and bushing motion, must be corrected in accordance with the Manager, Seattle Aircraft Certification Office. These types of damage are two links in a sequential chain of events that can ultimately result in a fractured lug, or other possible failure modes. Other types of damage (tool marks, scratched paint) are not related to the unsafe condition specified in this AD, and would be defined as superficial. The FAA has, however, added a “NOTE 2” to the final rule to define the word “damage.”

The FAA concurs with the second commenter's request to add another requirement to paragraph (c) of the final rule, which states that damage can be repaired in accordance with the applicable service bulletin. Paragraph (c) of the final rule has been revised to give the operator the option of either repair or replacement of the diagonal brace if any cracking or damage is detected, following accomplishment of any inspection required by paragraph (a) or (b) of the AD.

Request for Clarification of Paragraph (c) of the Proposed Rule

One commenter requests that the wording in paragraph (c) of the proposal be revised to read, “* * * and if one or more ligaments of the lugs are fractured perform additional inspections to detect damage of the strut secondary load paths * * *” The commenter notes that cracking, rather than fractures, will not increase the load in the secondary load path.

Another commenter requests clarification of the requirements in paragraph (c) of the proposal. The commenter questions which two lugs out of the four lugs (two lugs on the forward end and two lugs on the aft end) of the diagonal brace must be fractured before the extensive follow-on inspections of the secondary load path structure (Figure 8 of the service bulletin) are necessary. The commenter's interpretation is that the inspections specified in Figure 8 of the service bulletin are necessary only if both lugs on one of the ends of the diagonal brace are fractured, and if only one lug on each end of the diagonal brace is fractured, the inspections specified in Figure 7 of the service bulletin would be necessary.

The FAA agrees that clarification is necessary in order to better define the requirements in paragraph (c) of the AD. Paragraph (c) of the final rule has been revised to provide a detailed explanation of the inspection area and procedures.

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 208 airplanes of the affected design in the worldwide fleet. The FAA estimates that 105 airplanes of U.S. registry will be affected by this AD.

The inspections that are currently required by AD 99-07-06, and retained in this AD, take approximately 1 work hour per airplane 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 $6,300, or $60 per airplane, per inspection cycle.

The replacement that is required in this AD action takes approximately 8 work hours (4 work hours for each strut) per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will cost approximately $50,000 per airplane. Based on these figures, the cost impact of the required replacement required by this AD on U.S. operators is estimated to be $5,300,400, or $50,480 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 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.

§ 39.13

[Amended]

2. Section 39.13 is amended by removing amendment 39-11091 ( 64 FR 14578, March 26, 1999), and by adding a new airworthiness directive (AD), amendment 39-11659, to read as follows:

2000-07-05 Boeing: Amendment 39-11659. Docket 99-NM-72-AD. Supersedes AD 99-07-06, amendment 39-11091.

Applicability: Model 767 series airplanes; as listed in Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998; 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 cracking of the diagonal brace of the nacelle strut, which could result in failure of the diagonal brace, and consequent fatigue failure of a strut secondary load path and separation of the engine and strut, accomplish the following:

Initial Inspection

(a) Perform a detailed visual inspection to detect cracking or damage of the forward and aft lugs of the diagonal brace of the nacelle strut, on the left and right sides of the airplane, in accordance with Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998. Perform the inspection at the time specified in paragraph (a)(1) or (a)(2) of this AD, as applicable.

Note 2:

The word “damage” as referenced in this AD, is defined as fretting and/or bushing motion.

(1) For airplanes in Groups 1, 3, and 4: Inspect prior to the accumulation of 12,000 total flight cycles, or within 90 days after April 12, 1999 (the effective date of AD 99-07-06, amendment 39-11091), whichever occurs later.

(2) For airplanes in Group 2: Inspect prior to the accumulation of 24,000 total flight cycles, or within 90 days after April 12, 1999, whichever occurs later.

Follow-On Actions

(b) If no cracking or damage is detected during the inspection required by paragraph (a) of this AD, repeat the inspection thereafter at the interval specified in paragraph (b)(1) or (b)(2) of this AD, as applicable, in accordance with Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998. Repeat the inspection until the actions specified by paragraph (d) or (e) of this AD have been accomplished.

(1) For airplanes in Groups 1, 3, and 4; and for airplanes in Group 2 on which the diagonal brace has accumulated more than 32,000 total flight cycles: Repeat the inspection at intervals not to exceed 1,000 flight cycles.

(2) For airplanes in Group 2 on which the diagonal brace has accumulated 32,000 or fewer total flight cycles: Repeat the inspection at intervals not to exceed 3,000 flight cycles.

(c) If any cracking or damage is detected during any inspection required by paragraph (a) or (b) of this AD: Prior to further flight, remove the diagonal brace and perform additional inspections to detect damage of the strut secondary load paths, in accordance with Part 4 of Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998; and accomplish the requirements of paragraph (c)(1) or (c)(2) of this AD; as applicable.

(1) If any cracking is detected: Prior to further flight, accomplish the requirements of paragraph (c)(1)(i), (c)(1)(ii), or (c)(1)(iii) of this AD, as applicable.

(i) If one lug on one or both ends of the diagonal brace is fractured (Figure 7 of the alert service bulletin), or if two lugs on either end of the diagonal brace are fractured (Figure 8 of the alert service bulletin), prior to further flight: Rework the forward and aft lugs of the diagonal brace in accordance with the rework limits specified in Part 2 of the Accomplishment Instructions of the alert service bulletin.

(ii) Replace the one-piece diagonal brace with a new three-piece diagonal brace, in accordance with Part 3 of the Accomplishment Instructions of the alert service bulletin. Such replacement constitutes terminating action for the requirements of this AD.

(iii) If any additional damage of the alternate load paths is detected, 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 (DER) who has been authorized by the Manager, Seattle ACO, to make such findings.

(2) If any damage is detected: Prior to further flight, repair 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.

(d) For airplanes on which no cracking is detected during the inspection required by paragraph (a) of this AD, in lieu of accomplishing repetitive inspections in accordance with paragraph (b) of this AD, rework of the forward and aft lugs of the diagonal brace may be accomplished in accordance with Part 2 of the Accomplishment Instructions of Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998. If such rework is accomplished: Within 12,000 flight cycles after the rework, repeat the inspection required by paragraph (a) of this AD; and, prior to the accumulation of 37,500 total flight cycles on the diagonal brace, replace the one-piece diagonal brace with a new three-piece diagonal brace, in accordance with Part 3 of the Accomplishment Instructions of the alert service bulletin. Such replacement constitutes terminating action for the requirements of this AD.

Terminating Action

(e) Prior to the accumulation of 37,500 total flight cycles, or within 180 days after the effective date of this AD, whichever occurs later: Replace the one-piece diagonal brace with a new three-piece diagonal brace, in accordance with Part 3 of the Accomplishment Instructions of Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998. Such replacement constitutes terminating action for the requirements of this AD.

Alternative Methods 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 3:

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 §§ 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 by paragraphs (c)(1)(i) and (c)(3) of this AD, the actions shall be done in accordance with Boeing Alert Service Bulletin 767-54A0094, dated May 22, 1998. The incorporation by reference of this service bulletin was approved previously by the Director of the Federal Register as of April 12, 1999 (64 FR 14578, March 26, 1999). 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 May 15, 2000.

Issued in Renton, Washington, on March 31, 2000.

Donald L. Riggin,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.