01-9020. Airworthiness Directives; Boeing Model 737-700 and -800 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 737-700 and -800 series airplanes. This proposal would require inspections of certain tension bolts at the attachment of the aft pressure bulkhead to the fuselage at body station 1016 to determine if the correct parts are installed, and corrective action, if necessary. This action is necessary to prevent fatigue cracking along the bulkhead-to-fuselage attachment, which could result in structural failure of the aft pressure bulkhead and consequent rapid decompression of the airplane. This action is intended to address the identified unsafe condition.

DATES:

Comments must be received by May 29, 2001.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-403-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9 a.m. and 3 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-403-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:

Nenita Odesa, 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-403-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-403-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

The FAA has received a report that numerous Boeing Model 737-700 and -800 series airplanes may have been delivered with the wrong tension bolts or nuts installed at the attachment of the aft pressure bulkhead to the fuselage at body station (BS) 1016. The subject tension bolts attach the forward frame chord, the Y-chord, and the aft frame chord to the fuselage, and the bolts may be the wrong length or the wrong nut could be installed. If incorrect tension bolts are installed, the fatigue life of the aft pressure bulkhead may be reduced. This condition, if not corrected, could result in fatigue cracking along the bulkhead-to-fuselage attachment, structural failure of the aft pressure bulkhead, and consequent rapid decompression of the airplane.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Service Bulletin 737-53-1212, including Appendix A, dated August 13, 1998, which describes procedures for various inspections of tension bolts at the attachment of the aft pressure bulkhead to the fuselage at BS 1016 to determine whether the correct parts are installed. The inspections include:

• A visual inspection of the nuts above stringer 10 on both sides of the airplane, measuring the height of the nut to determine if the correct nut is installed.
• An inspection of bolts using a special measuring gage to determine if any long bolts are installed.
• A visual inspection of bolts to determine if any short bolts are installed.
• A torque test of the nuts on any long bolts found above the main deck floor to determine whether the bolts are properly clamped.

Corrective actions are also described in the service bulletin. If any long or short bolt is installed, the corrective action is replacement of the bolt and nut, as applicable. In cases where short bolts are installed between two adjacent stringer end fittings or at stringer end fittings, repetitive inspections of the nuts to determine if bolts are properly clamped are provided as an option that extends the compliance time for the replacement of bolts. The compliance time for the replacement of bolts varies by condition, and Section 1.D. (“Compliance”) of the service bulletin contains a table summarizing the conditions, appropriate corrective actions, and compliance times.

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

Operators should note that, although the service bulletin refers to visual inspections, this proposed AD identifies these inspections as “special detailed inspections.” A note defining a special detailed inspection is included after paragraph (a) of this AD.

Operators should also note that, although the service bulletin specifies that the manufacturer must be contacted for disposition of certain repair conditions, this proposed AD would require those conditions to be repaired per a method approved by the FAA, or per data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the FAA to make such findings.

Cost Impact

There are approximately 31 airplanes of the affected design in the worldwide fleet. The FAA estimates that 14 airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately 2 work hours per airplane to accomplish the proposed inspections, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be $1,680, or $120 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-403-AD.

Applicability: Model 737-700 and -800 series airplanes; line numbers 4, 6, 9 through 20 inclusive, 29, and 31 through 46 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 (d) 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 along the bulkhead-to-fuselage attachment, which could result in structural failure of the aft pressure bulkhead and consequent rapid decompression of the airplane, accomplish the following:

Inspections and Corrective Actions

(a) Prior to the accumulation of 3,000 total flight cycles, or within 90 days after the effective date of this AD, whichever occurs later, do one-time special detailed inspections of tension bolts at the attachment of the aft pressure bulkhead to the fuselage at body station 1016 to determine whether the correct parts are installed, per the Accomplishment Instructions of Boeing Service Bulletin 737-53-1212, including Appendix A, dated August 13, 1998.

(1) If any long bolt is found above the main deck floor, do paragraphs (a)(1)(i) and (a)(1)(ii) of this AD.

(i) Before further flight, do a torque test of the nut on the long bolt to determine whether the bolt is properly clamped.

(ii) Replace the bolt and nut, as applicable, with new parts, per the service bulletin, except as provided by paragraph (c) of this AD. The correct replacement parts are listed in Figure 4 of the service bulletin. Do the replacement no later than the compliance time specified in the compliance table in Section 1.D. (“Compliance”) of the service bulletin. For the purposes of this AD, compliance times stated in flight cycles and years are to be counted from the time of the inspection per paragraph (a) of this AD.

(2) For any long or short bolt other than those identified in paragraph (a)(1) of this AD, replace the bolt and nut, as applicable, with new parts, per the service bulletin, except as provided by paragraph (c) of this AD. The correct replacement parts are listed in Figure 4 of the service bulletin. Do the replacement no later than the compliance time specified in the compliance table in Section 1.D. (“Compliance”) of the service bulletin. For the purposes of this AD, compliance times stated in flight cycles and years are to be counted from the time of the inspection per paragraph (a) of this AD.

Note 2:

For the purposes of this AD, a special detailed inspection is defined as: “An intensive examination of a specific item(s), installation, or assembly to detect damage, failure, or irregularity. The examination is likely to make extensive use of specialized inspection techniques and/or equipment. Intricate cleaning and substantial access or disassembly procedures may be required.”

Repetitive Inspections

(b) Where short bolts are installed between two adjacent stringer end fittings or at stringer end fittings, doing repetitive inspections of the nuts to determine if bolts are properly clamped, per Boeing Service Bulletin 737-53-1212, including Appendix A, dated August 13, 1998, extends the compliance time for the replacement of bolts, per the compliance table in Section 1.D. (“Compliance”) of the service bulletin.

Exception for Certain Repair Conditions

(c) Where Boeing Service Bulletin 737-53-1212, including Appendix A, dated August 13, 1998, specifies to contact Boeing for replacement instructions: Before further flight, replace per a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA; or per data meeting the type certification basis of the airplane approved by 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 approval letter must specifically reference this AD.

Alternative Methods of Compliance

(d) 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

(e) 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.

Issued in Renton, Washington, on April 5, 2001.

Donald L. Riggin,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.