AD 94-15-06

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) by superseding AD 90-01-07, amendment 39-6440 (55 FR 255, January 4, 1990), which is applicable to certain Boeing Model 747 series airplanes, was published in the Federal Register on February 3, 1994 (59 FR 5139). The action proposed to require inspection of an expanded area, deletion of the reporting requirement, and expansion of the applicability.

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

One commenter supports the proposed rule.

Two commenters request that proposed paragraph (e) be revised to reduce the area of inspection to coincide with the area specified in the service bulletin (Boeing Service Bulletin 747- 53A2312, Revision 2, dated October 8, 1992) referenced in the proposal as the appropriate source of service information. The FAA does not concur. An FAA investigation has revealed that countersunk fasteners may be installed in areas other than those specified in the referenced service bulletin. Therefore, the FAA has determined that a one-time inspection along the entire lap joint of the skin panel must be accomplished to positively confirm the exact location of these countersunk fasteners.

One commenter requests an extension to the proposed compliance time of 11,000 total landings to conduct the high frequency eddy current (HFEC) inspection required by paragraph (g) of the proposal. The commenter states that the compliance time should coincide with the time recommended in the service bulletin (Boeing Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992) referenced in the proposal as the appropriate source of service information. The compliance time in the service bulletin specifies that, for airplanes on which only the minimum number of countersunk fasteners have been installed, the HFEC inspection should commence at 20,000 total flight cycles. The commenter notes that for airplanes on which only the minimum number of countersunk fasteners have been installed, the potential for widespread multi-site damage is significantly lessened than for airplanes on which more than the minimum number of countersunk fasteners have been installed.

The FAA does not concur with the commenter's request to extend the compliance time. In developing an appropriate compliance time for this action, the FAA considered the safety implications of any cracking in this area. The FAA acknowledges that cracking in the upper row of countersunk fasteners in the lap splice in the area adjacent to the wing-to-body fairing intersection may not result in catastrophic consequences; however, the FAA finds that any cracking in this area has the potential for developing into an unsafe condition. This AD is issued to address that unsafe condition, which may result in reduced structural integrity of the fuselage of the airplane as a result of cracking in these areas. Further, since cracking has been found in this area on in-service airplanes that had accumulated less than 20,000 total flight cycles, the FAA has determined that 11,000 total landings represent the maximum interval of time allowable wherein the inspection can reasonably be accomplished and an acceptable level of safety can be maintained.

One commenter requests clarification of the proposed compliance time for reinspection of previously modified lap joints. The commenter requests that the HFEC inspections required by proposed paragraph (k) commence from the time the lap joint was modified in accordance with AD 90-01-07, rather than from the time the lap joint is modified in accordance with proposed paragraph (j). The FAA finds that clarification is warranted. Paragraph (k) of the final rule has been revised to state that HFEC inspections are to be performed prior to the accumulation of 10,000 total landings following modifications (of locations where countersunk fasteners were found) accomplished in accordance with Boeing Service Bulletin 747-53A2312, dated June 12, 1989, Revision 1, dated March 29, 1990, or Revision 2, dated October 8, 1992, which includes modifications accomplished in accordance with AD 90-01-07 or in accordance with paragraph (j) of this AD.

Two commenters question the necessity for the inspections following modification of the lap joints required by proposed paragraph (k). One of these commenters does not see adequate justification for requiring these inspections since AD 90-01-07 terminated the inspections after accomplishment of the modification. The other commenter states that, since other lap joints are not required to be inspected following modification, this lap joint should not be inspected following modification. From these comments, the FAA infers that these commenters are requesting that the requirement to inspect following modification be deleted. The FAAdoes not concur. An FAA evaluation of currently available inspection techniques reveals that current technology may not be able to adequately detect cracking beneath protruding head fasteners. Further, in-service experience has demonstrated that cracking has gone undetected beneath these protruding head fasteners. Therefore, the FAA's intent in requiring these inspections following the modification are to detect any cracking that may develop after accomplishment of the modification and to repair any cracking prior to it adversely affecting the structural integrity of the fuselage of the airplane.

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

There are approximately 723 Boeing Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 183 airplanes of U.S. registry will be affected by this AD.

The inspections that were previously required by AD 90-01-07, and retained in this AD, take approximately 14 work hours per airplane to accomplish, at an average labor rate of $55 per work hour. Based on these figures, the total cost impact of these inspection requirements of this AD on U.S. operators is estimated to be $140,910, or $770 per airplane, per inspection cycle.

The additional new inspections that are required by this AD will take approximately 82 work hours per airplane to accomplish, at an average labor rate of $55 per work hour. Based on these figures, the total cost impact of these inspection requirements of this AD on U.S. operators is estimated to be $825,330, or $4,510 per airplane, per inspection cycle.

The modification required by this AD will take approximately 124 work hours per airplane to accomplish, at an average labor rate of $55 per work hour. Required parts will be nominal in cost. Based on these figures, the total cost impact of the modification requirements of this AD on U.S. operators is estimated to be $1,248,060, or $6,820 per airplane.

Based on the above figures, the total cost impact of the inspection and modification requirements of this AD on U.S. operators is estimated to be $2,214,300, or $11,407 per airplane.

The total cost impact figure discussed above is 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.

The FAA recognizes that the modification will require a large number of work hours to accomplish. However, the 20,000-landings compliance time specified in paragraph (j) of this AD should allow ample time for the modification of all countersunk fasteners locations to be accomplished coincidentally with scheduled major airplane inspection and maintenance activities, thereby minimizing the costs associated with special airplane scheduling.

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. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. § 39.13 - (Amended)

2. Section 39.13 is amended by removing amendment 39-6440 (55 FR 255, January 4, 1990), and by adding a new airworthiness directive (AD), amendment 39-8977, to read as follows: