01-14045. Airworthiness Directives; Boeing Model 707 and 720 Series Airplanes

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 707 and 720 series airplanes. This proposal would require a preventive modification of the front spar fitting on the outboard engine nacelle. This action is necessary to prevent fatigue cracking of the front spar fitting on the outboard engine nacelle, which could reduce the structural integrity of the nacelle, and result in separation of the engine from the airplane. This action is intended to address the identified unsafe condition.

DATES:

Comments must be received by July 20, 2001.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-378-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. Comments may be submitted via fax to [phone]. Comments may also be sent via the Internet using the following address: [e-mail]. Comments sent via fax or the Internet must contain “Docket No. 2000-NM-378-AD” in the subject line and need not be submitted in triplicate. Comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 for Windows or ASCII text.

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:

Duong Tran, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone [phone]; fax [phone].

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 action may be changed in light of the comments received.

Submit comments using the following format:

• Organize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues.
• For each issue, state what specific change to the proposed AD is being requested.
• Include justification (e.g., reasons or data) for each request.

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 filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this action must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2000-NM-378-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. 2000-NM-378-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

The FAA has received reports that fatigue cracks have been found in the front spar fitting on the outboard engine nacelle on certain Boeing Model 707 and 720 series airplanes. The cracks originated at the rearmost of the seven fasteners which attach the front spar fitting to the front spar chord. Such cracking, if not corrected, could reduce the structural integrity of the nacelle, and result in separation of the engine from the airplane.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Service Bulletin 1541, Revision 3, dated February 15, 1967, which describes procedures for, among other actions, installation of a preventive modification of the front spar fitting on the outboard engine nacelle. The modification involves replacement of the front spar fitting with a new, improved (stronger) fitting and modification of the front spar chord to distribute stress loads over the entire front spar fitting. 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 actions specified in the service bulletin described previously, except as discussed below.

Differences Between Proposed Rule and Service Bulletin

This proposed rule differs from the service bulletin in the compliance time for the proposed modification. For certain airplanes, the service bulletin recommends accomplishment of the modification of the front spar fitting, but does not specify a compliance time; for other airplanes, the service bulletin specifies that the modification is optional and may be installed on an attrition basis. This proposed AD would require installation of the modification prior to the accumulation of 20,000 total flight cycles, or within 24 months after the effective date of this AD, whichever occurs later. In developing an appropriate compliance time for this AD, the FAA considered not only the manufacturer's recommendation, but the degree of urgency associated with addressing the subject unsafe condition, the average utilization of the affected fleet, and the time necessary to perform the actions. In light of all of these factors, the FAA finds that the proposed compliance time for completing the required actions represents an appropriate interval of time allowable for affected airplanes to continue to operate without compromising safety.

The proposed rule also differs from the service bulletin in that it would not require the repetitive inspections to detect cracking of the front spar fitting, which are described in the service bulletin. The decision to mandate the preventive modification of the front spar fitting is based on the FAA's determination that long-term continued operational safety will be better assured by design changes to remove the source of the problem, rather than by repetitive inspections. Long-term inspections may not provide the degree of safety assurance necessary for the transport airplane fleet. This, coupled with a better understanding of the human factors associated with numerous continual inspections, has led the FAA to consider placing less emphasis on inspections and more emphasis on design improvements. The proposed modification requirement is consistent with these findings.

Operators should note that Section 3., Part II, “l,” of the service bulletin refers to an incorrect part number for the new, improved front spar fitting. That item reads, “Install applicable new fitting 65-13347-4* * *”; the FAA has determined that the correct part number for the new, improved fitting in this case is 65-13347-5. Figure 1 of the service bulletin references the correct part number.

Cost Impact

There are approximately 13 airplanes of the affected design in the worldwide fleet. The FAA estimates that 3 airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately 64 work hours per airplane to accomplish the proposed modification, and that the average labor rate is $60 per work hour. Required parts would cost approximately $1,300 per airplane. Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be $15,420, or $5,140 per airplane.

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 proposed AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions.

Regulatory Impact

The regulations proposed herein would 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 proposal would not have federalism implications under Executive Order 13132.

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

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 adding the following new airworthiness directive:

Boeing: Docket 2000-NM-378-AD.

Applicability: Model 707 and 720 series airplanes, listed in Boeing Service Bulletin 1541, Revision 3, dated February 15, 1967; 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 (c) 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 of the front spar fitting on the outboard engine nacelle, which could reduce the structural integrity of the nacelle, and result in separation of the engine from the airplane, accomplish the following:

Preventive Modification

(a) Prior to the accumulation of 20,000 total flight cycles, or within 24 months after the effective date of this AD, whichever occurs later, install the preventive modification of the front spar fitting on the outboard engine nacelle. Do the modification (including replacement of the front spar fitting with a new, improved (stronger) fitting, and modification of the front spar chord to distribute stress loads over the entire front spar fitting) according to Boeing Service Bulletin 1541, Revision 3, dated February 15, 1967.

Note 2:

Modification of the front spar fitting on the outboard engine nacelle (including replacement of the front spar fitting with a new, improved (stronger) fitting, and modification of the front spar chord to distribute stress loads over the entire front spar fitting) accomplished prior to the effective date of this AD according to Boeing Service Bulletin 1541, dated July 1, 1962; Revision 1, dated January 29, 1963; Revision 2, dated February 11, 1964; or Supplement 1541(R-2)A, dated April 2, 1964; is acceptable for compliance with the requirements of paragraph (a) of this AD.

Spares

(b) As of the effective date of this AD, no person shall install a front spar fitting, part number 65-2532 or 65-2532-5, on the outboard engine nacelle on any airplane.

Alternative Methods of Compliance

(c) 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. 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

(d) 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.

Issued in Renton, Washington, on May 30, 2001.

Vi L. Lipski,

Manager, Transport Airplane Directorate, Aircraft Certification Service.