Airworthiness directives: Boeing,
[Federal Register: August 20, 1999 (Volume 64, Number 161)]
[Proposed Rules]
[Page 45483-45485]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr20au99-29]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 99-NM-125-AD]
RIN 2120-AA64
Airworthiness Directives; Boeing Model 757 Series Airplanes Equipped With Rolls Royce Engines
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed rulemaking (NPRM).
SUMMARY: This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 757 series airplanes. This proposal would require modification of the nacelle strut and wing structure of certain Boeing Model 757 series airplanes equipped with Rolls Royce RB211 engines. This proposal is prompted by reports indicating that the actual operational loads applied to the nacelle are higher than the analytical loads that were used during the initial design. Such an increase in loading can lead to fatigue cracking in primary strut structure prior to an airplane's reaching its design service objective. The actions specified by the proposed AD are intended to prevent fatigue cracking in primary strut structure and consequent reduced structural integrity of the strut.
DATES: Comments must be received by October 4, 1999.
ADDRESSES: Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 99-NM-125-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal holidays.
The service information referenced in the proposed rule may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207.
This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington.
FOR FURTHER INFORMATION CONTACT: Rick Kawaguchi, Aerospace Engineer,Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-1153; fax (425) 227-1181.
SUPPLEMENTARY INFORMATION:
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 filedin 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 99-NM-125-AD.'' The postcard will be date stamped and returned to the commenter.
Availability of NPRMs
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. 99-NM-125-D, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.
Discussion
The FAA has received reports indicating that the manufacturer has accomplished a structural reassessment of the damage tolerance capabilities of the Boeing Model 757 series airplane, equipped with Rolls Royce engines. This reassessment indicates that the actual operational loads applied to the nacelle strut and wing structure are higher than the analytical loads that were used during the initial design. Subsequent analysis and service history, which includes numerous reports of fatigue cracking on certain strut and wing structure, indicate that fatigue cracking can occur on the primary strut structure before an airplane reaches its design service objective of 20 years or 50,000 flight cycles. Analysis also indicates that such cracking, if it were to occur, would grow at a much greater rate than originally expected. Fatigue cracking in primary strut structure would result in reduced structural integrity of the strut.
Explanation of Relevant Service Information
Boeing recently has developed a modification of the strut-to-wing attachment structure installed on Model 757 series airplanes equipped with Rolls Royce Model RB211 series engines. This modification significantly improves the load-carrying capability and durability of the strut-to-wing attachments. Such improvement also will substantially reduce the possibility of fatigue cracking and corrosion developing in the attachment assembly.
The FAA has reviewed and approved Boeing Service Bulletin 757-54- 0035, dated July 17, 1997, which describes procedures to modify the nacelle strut
[[Page 45484]]
and wing structure of certain Boeing Model 757 series airplanes equipped with Rolls Royce RB211 engines. The modification consists of replacing many of the significant load-bearing components of the strut (e.g., the side link fittings assemblies, the upper link assembly, certain fuse bolt assemblies, etc.) with improved components. In addition, Table I of the service bulletin also identifies numerous related service bulletin modifications that must be accomplished before or at the same time as the service bulletin is accomplished. These modifications also entail the replacement of many of the significant load-bearing components of the strut with improved components.
In addition, the service bulletin contains a formula for calculating an optional compliance threshold for the specified modification. This formula is intended to be used as an alternative to the 20-year calendar threshold specified in the service bulletin.
Accomplishment of the actions specified in the service bulletin is intended to adequately address the identified unsafe condition.
Explanation of Requirements of Proposed Rule
Since an unsafe condition has been identified that is likely to exist or develop on other products of this same type design, the proposed AD would require accomplishment of the modifications specified in the service bulletin described previously, except as discussed below.
Differences Between Proposed Rule and Service Bulletin
Operators should note that this proposed AD would provide a grace period of 3,000 flight cycles for airplanes that have already passed the initial compliance threshold specified in the service bulletin. The service bulletin was issued at a time when none of the affected airplanes had reached that initial compliance threshold.
Cost Impact
There are approximately 394 airplanes of the affected design in the worldwide fleet. The FAA estimates that 176 airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately 1,049 work hours per airplane to accomplish the proposed modification, and that the average labor rate is $60 per work hour. This work hour figure includes the time it would take to remove and reinstall the struts from the airplane as well as the time to gain and close access to the adjacent wing structure. Based on these figures, the cost impact of the modification proposed by this AD on U.S. operators is estimated to be $11,077,440, or $62,940 per airplane.
This cost impact figure does not reflect the cost of the terminating actions described in the service bulletins listed in paragraph I.C., Table I, ``Strut Improvement Bulletins,'' on page 6 of Boeing Service Bulletin 757-54-0035, that are proposed to be accomplished prior to, or concurrently with, the modification of the nacelle strut and wing structure. Since some operators may have accomplished certain modifications on some or all of the airplanes in its fleet, while other operators may not have accomplished any of the modifications on any of the airplanes in its fleet, the FAA is unable to provide a reasonable estimate of the cost of accomplishing the terminating actions described in the service bulletins listed in Table I of the service bulletin. As indicated earlier in this preamble, the FAA invites comments specifically on the overall economic aspects of this proposed rule. Any data received via public comments to this notice will aid the FAA in developing an accurate accounting of the cost impact of the rule.
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. However, the FAA has been advised that manufacturer warranty remedies are available for part costs associated with accomplishing the actions required by this proposed AD. Therefore, the future economic cost impact of this rule on U.S. operators may be less than the cost impact figure indicated above.
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
-
The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
-
Section 39.13 is amended by adding the following new airworthiness directive:
Boeing: Docket 99-NM-125-AD.
Applicability: Model 757 series airplanes equipped with Rolls Royce engines, line numbers 1 through 735 inclusive; 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 (b) 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 fatigue cracking in primary strut structure and consequent reduced structural integrity of the strut, accomplish the following:
(a) Modify the nacelle strut and wing structure in accordance with Boeing Service Bulletin 757-54-0035, dated July 17, 1997, at the later of the times specified in paragraph (a)(1) or (a)(2). All of the terminating actions described in the service bulletins listed in paragraph I.C., Table I, ``Strut Improvement Bulletins,'' on page 6 of Boeing Service Bulletin 757-54-0035, must be accomplished in accordance with those service bulletins prior to, or concurrently with, the
[[Page 45485]]
accomplishment of the modification of the nacelle strut and wing structure required by this paragraph.
(1) Prior to the accumulation of 37,500 total flight cycles, or prior to 20 years since the date of manufacture of the airplane, whichever occurs first.
(2) Within 3,000 flight cycles after the effective date of this AD.
Alternative Methods of Compliance
(b) 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 2: 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
(c) Special flight permits may be issued in accordance with Secs. 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 August 16, 1999. D.L. Riggin, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.
[FR Doc. 99-21685Filed8-19-99; 8:45 am]
BILLING CODE 4910-13-P
