01-28798. Airworthiness Directives; Boeing Model 737-100, -200, -200C, -300, -400, and -500 Series Airplanes

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Boeing Model 737 series airplanes. The existing AD currently requires repetitive inspections for cracking and corrosion of the pressure bulkhead at body station (BS) 1016, and follow-on actions. This action would expand the applicability of the existing AD to include additional airplanes and require new repetitive inspections to detect cracking and corrosion of the aft pressure bulkhead at BS 1016, and follow-on actions. This action is necessary to detect and correct corrosion or cracking of the aft pressure bulkhead at BS 1016, which could result in loss of the aft pressure bulkhead web and stiffeners and consequent rapid decompression of the fuselage. This action is intended to address the identified unsafe condition.

DATES:

Comments must be received by January 3, 2002.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-359-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-359-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:

Scott Fung, 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-359-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-359-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

On December 6, 1985, the FAA issued AD 84-20-03 R1, amendment 39-5183 (50 FR 51235, December 16, 1985), applicable to certain Boeing Model 737 series airplanes, to require repetitive inspections for cracking and corrosion of the pressure bulkhead at body station (BS) 1016, and follow-on actions. That action was prompted by reports indicating that cracking or corrosion and cracking had been found on several Boeing Model 737-200 series airplanes at the lower central web and stiffeners of the pressure bulkhead at BS 1016. The requirements of that AD are intended to detect and correct such corrosion and cracking, which could result in reduced structural integrity of the aft pressure bulkhead.

Actions Since Issuance of Previous Rule

Since the issuance of that AD, we have received reports of severe corrosion in the area affected by the existing AD on other Model 737 series airplanes which are not included in the applicability of the existing AD. In addition, we have determined that the instructions for the inspections required by the existing AD are not adequate in defining the inspection level and area, nor are the instructions adequate for gaining access and preparing for the inspection.

Explanation of Relevant Service Information

We have reviewed and approved Boeing Alert Service Bulletin 737-53A1075, Revision 3, dated June 8, 2000. (The existing AD shows Boeing Service Bulletin 737-53-1075, Revision 1, dated September 2, 1983, as the appropriate source of service information for accomplishment of the actions required by that AD.) Revision 3 of the service bulletin describes procedures for repetitive detailed visual inspections for cracking and corrosion of the aft pressure bulkhead at BS 1016, including inspections of the following items: Forward and aft sides of the pressure web, forward and aft sides of the pressure chord, pressure chord radius, forward and aft sides of the angle stiffener, forward and aft chord, stringer end fitting, system penetration doublers, channel stiffeners and fasteners, “Z” stiffeners and fasteners, and fasteners common to the pressure chord and pressure web. The service bulletin also describes follow-on actions to these inspections, which involve repair, if necessary, as well as clearing the drain path to ensure that it is free of debris, enlarging the drain hole, and replacing existing leveling compound, if necessary. Accomplishment of the actions shown 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 supersede AD 84-20-03 R1 to continue to require repetitive detailed visual inspections for cracking and corrosion of the pressure bulkhead at BS 1016, and follow-on actions. This action would require new repetitive inspections to detect cracking and corrosion of the aft pressure bulkhead at BS 1016 and follow-on actions, and would require these inspections to be accomplished on airplanes not subject to the existing AD. The actions would be required to be accomplished according to Revision 3 of the service bulletin described previously, except as discussed below.

Differences Between Proposed AD and Service Bulletin

This proposed AD differs from Revision 3 of the service bulletin in this way: The service bulletin states that the manufacturer must be contacted for disposition of certain repair conditions, but this proposed AD would require the repair of those conditions to be accomplished 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 Manager, Seattle Aircraft Certification Office, to make such findings.

Explanation of Changes to Requirements of Existing AD

We have revised the requirements of the existing AD, as restated in this proposed AD, to remove all references to the use of “later FAA-approved revisions of the applicable service bulletin.” This change is consistent with FAA policy in that regard. In place of this language, we have revised the existing requirements restated in this proposed AD to provide for accomplishment of actions per Revision 1, Revision 2, or Revision 3 of the service bulletin. We have determined that this change will not increase the economic burden on any operator, nor will it increase the scope of the proposed AD.

Explanation of Repetitive Interval

For certain airplanes, the proposed AD would require repetitive inspections at least every two years. For other airplanes, the repetitive interval is four years. This difference is due to design changes to improve corrosion resistance in the subject area. For example, airplanes with line numbers 1 through 929 inclusive have a single 0.25-inch drain hole (which the existing AD requires to be expanded to 0.5 inch), and airplanes with line numbers 930 through 1042 inclusive have a single 0.5-inch drain hole. This proposed AD would require repetitive inspections on these airplanes at least every two years. However, airplanes with line numbers 1043 through 3132 have TWO 0.5-inch drain holes. We find that the addition of a second drain hole on these airplanes, as well as improvements to the leveling compound and finishes that are present on airplanes with line numbers 930 through 3132 inclusive provides additional corrosion resistance. Thus, this proposed AD would require repetitive inspections on these airplanes at least every four years.

Cost Impact

There are approximately 2,920 airplanes of the affected design in the worldwide fleet.

We estimate that 337 airplanes of U.S. registry are subject to the existing AD. The inspections that are currently required by AD 84-20-03 R1 take approximately 2 work hours 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 $40,440, or $120 per airplane, per inspection cycle.

The drain hole enlargement that is currently required by AD 84-20-03 R1 takes approximately 2 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of this currently required action on U.S. operators is estimated to be $40,440, or $120 per airplane.

We estimate that 1,143 airplanes of U.S. registry would be affected by this proposed AD. The new inspections that are proposed in this AD action would take approximately 4 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of these new proposed requirements on U.S. operators is estimated to be $274,320, or $240 per airplane, per inspection cycle.

The cost impact figures discussed above are 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 removing amendment 39-5183 (50 FR 51235, December 16, 1985), and by adding a new airworthiness directive (AD), to read as follows:

Boeing: Docket 2000-NM-359-AD. Supersedes AD 84-20-03 R1, Amendment 39-5183.

Applicability: Model 737-100, -200, -200C, -300, -400, and -500 series airplanes; line numbers (L/N) 1 through 3132 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 (h)(1) 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 detect and correct corrosion or cracking of the aft pressure bulkhead at Body Station (BS) 1016, which could result in loss of the aft pressure bulkhead web and stiffeners and consequent rapid decompression of the fuselage, accomplish the following:

Restatement of Requirements of AD 84-20-03 R1

Initial Inspection

(a) For Model 737 series airplanes with L/N 1 through 929 inclusive, with more than 20,000 hours time-in-service or 7 years since date of manufacture, whichever occurs first: Within 120 days after January 20, 1986 (the effective date of AD 84-20-03 R1, amendment 39-5183), unless already accomplished within the 21 months before January 20, 1986, visually inspect the BS 1016 pressure bulkhead for cracking and corrosion; according to Boeing Alert Service Bulletin 737-53A1075, Revision 1, dated September 2, 1983; Revision 2, dated July 13, 1984; or Revision 3, dated June 8, 2000. Remove any obstruction to the drain hole in the frame chord and replace any deteriorated leveling compound as noted in the service bulletin. Treat the area of inspection with corrosion inhibitor BMS 3-23, or equivalent.

Drain Hole Enlargement

(b) For airplanes identified in paragraph (a) of this AD: Within 1 year after January 20, 1986, accomplish the drain hole enlargement as shown in Boeing Alert Service Bulletin 737-53A1075, Revision 1, dated September 2, 1983; Revision 2, dated July 13, 1984; or Revision 3, dated June 8, 2000.

Corrective Action

(c) If cracking or corrosion is found during any inspection required by paragraph (a) or (d) of this AD, before further flight, repair according to paragraph (c)(1) or (c)(2) of this AD.

(1) According to Boeing Alert Service Bulletin 737-53A1075, Revision 1, dated September 2, 1983; Revision 2, dated July 13, 1984; or Revision 3, dated June 8, 2000.

(2) According to 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 (DER) 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 Manager's approval letter must specifically reference this AD.

Repetitive Inspections

(d) For airplanes identified in paragraph (a) of this AD: Repeat the visual inspections and corrosion inhibitor treatment in paragraph (a) at intervals not to exceed 2 years, until paragraph (e) of this AD has been done.

New Requirements of This AD

Initial Inspection

(e) Do a detailed visual inspection for cracking or corrosion of the aft pressure bulkhead at BS 1016 (including the forward and aft sides of the pressure web, forward and aft sides of the pressure chord, pressure chord radius, forward and aft sides of the angle stiffener, forward and aft chord, stringer end fitting, system penetration doublers, channel stiffeners and fasteners, “Z” stiffeners and fasteners, and fasteners common to the pressure chord and pressure web), according to Boeing Alert Service Bulletin 737-53A1075, Revision 3, dated June 8, 2000. Do this inspection at the applicable time shown in paragraph (e)(1), (e)(2), or (e)(3) of this AD.

Note 2:

For the purposes of this AD, a detailed visual inspection is defined as: “An intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required.”

(1) For airplanes on which an inspection has previously been done according to the requirements of paragraph (a) of this AD: Do the inspection within 2 years since the most recent inspection according to paragraph (a) or (d) of this AD, as applicable. Inspection according to paragraph (e) of this AD ends the requirement for inspections according to paragraph (d) of this AD.

(2) For airplanes having L/N 930 through 1042 inclusive, on which an inspection has not previously been done according to paragraph (a) of this AD: Do the inspection within 2 years after the effective date of this AD.

(3) For airplanes having L/N 1043 through 3132 inclusive, on which an inspection has not previously been done according to paragraph (a) of this AD: Do the inspection within 6 years since the airplane's date of manufacture, or within 2 years after the effective date of this AD, whichever occurs later.

Repetitive Inspections

(f) Repeat the inspection in paragraph (e) of this AD at the applicable time shown in paragraph (f)(1) or (f)(2) of this AD.

(1) For airplanes having L/N 1 through 1042 inclusive: Repeat the inspection at least every 2 years.

(2) For airplanes having L/N 1043 through 3132 inclusive: Repeat the inspection at least every 4 years.

Repair

(g) If any corrosion or cracking is found during any inspection according to paragraph (e) or (f) of this AD: Before further flight, repair according to Boeing Alert Service Bulletin 737-53A1075, Revision 3, dated June 8, 2000. EXCEPTION: If corrosion or cracking of the web and stiffeners is outside the limits specified in the service bulletin, or if corrosion or cracking is found in any structure not covered by the repair instructions in the service bulletin, before further flight, repair according to a method approved by the Manager, Seattle ACO, or per 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. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the Manager's approval letter must specifically reference this AD.

Alternative Methods of Compliance

(h)(1) 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.

(2) Alternative methods of compliance, approved previously in accordance with AD 84-20-03 R1, amendment 39-5183, are approved as alternative methods of compliance with this AD.

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

(i) 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 November 9, 2001.

Vi L. Lipski,

Manager, Transport Airplane Directorate, Aircraft Certification Service.