01-19261. Airworthiness Directives; Boeing Model 737-100, -200, -200C, -300, -400, and -500 Series Airplanes

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Supplemental notice of proposed rulemaking; reopening of comment period.

SUMMARY:

This document revises an earlier proposed airworthiness directive (AD); applicable to certain Boeing Model 737-100, -200, and -200C series airplanes; which would have required inspections for corrosion and cracking of the inboard track of each outboard flap, and repair, if necessary, and would have provided an optional terminating action. This new action expands the applicability and removes the optional terminating action of the proposed AD. For certain airplanes, this action would require new repetitive inspections for discrepancies of the rear spar attachments and cracks in the upper flange of the inboard track at the rear spar attachment of each outboard flap, and eventual rework of the flap track assembly and rear spar attachments, including replacement of the flap track with a new track, if necessary. For all airplanes, this action would require repetitive inspections for cracks in the upper flange of the inboard flap tracks at the rear spar attachments, and corrective action, if necessary. These actions are necessary to find and fix discrepancies of the inboard tracks of the outboard flaps, which could result in loss of the outboard trailing edge flaps and consequent reduced controllability of the airplane. These actions are intended to address the identified unsafe condition.

DATES:

Comments must be received by September 6, 2001.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 99-NM-21-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. 99-NM-21-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:

James Blilie, 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 document 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 filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this proposal must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 99-NM-21-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-21-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to add an airworthiness directive (AD), applicable to certain Boeing Model 737-100, -200, and -200C series airplanes, was published as a notice of proposed rulemaking (NPRM) in the Federal Register on April 26, 1999 (64 FR 20224). That NPRM would have required inspections to detect corrosion and cracking of the inboard track of each outboard flap where the track attaches to the rear spar, and repair, if necessary. For certain airplanes, that proposal also would have provided optional terminating action for the proposed repetitive inspections for those airplanes. That NPRM was prompted by several reports of cracking of the inboard track of the outboard flap. That condition, if not corrected, could result in loss of the outboard trailing edge flap and consequent reduced controllability of the airplane.

Explanation of New Service Information

Since the issuance of that NPRM, the FAA has reviewed and approved Boeing Service Bulletin 737-57A1249, Revision 1, including Appendix A, dated June 1, 2000. That service bulletin describes procedures for repetitive detailed visual inspections to find discrepancies (including corrosion, or missing, damaged, or migrated anti-fret strips and tapered shims) of the rear spar attachments of the flap tracks. That service bulletin also describes procedures for repetitive detailed visual, high frequency eddy current (HFEC), and ultrasonic inspections to find cracking in the upper flange of the inboard track of each outboard flap at the rear spar attachment. The service bulletin also describes procedures for rework of the flap track assembly and rear spar attachments. The rework procedures include the following:

• Removal of the flap track.
• A detailed visual inspection for a missing, damaged, or migrated anti-fret strip and tapered shim of the rear spar attachments of the flap tracks; replacement of the anti-fret strip with a new aluminum anti-fret strip (or installation of an aluminum strip if no strip is installed), if necessary; and replacement of the tapered shim with a new shim (or installation of a shim if no shim is installed).
• Eddy current and ultrasonic inspections for fatigue cracking of the flap tracks.
• A detailed visual inspection for corrosion of the flap tracks.
• Rework of attachment holes.
• Replacement of the flap track with a new track, if necessary.

The procedures described in Boeing Service Bulletin 737-57A1249, Revision 1, are similar to the procedures described in Boeing Service Bulletin 737-57-1065, Revision 3, dated December 17, 1982, which was referenced in the original NPRM as the appropriate source of service information for certain proposed actions. Among other things, however, Boeing Service Bulletin 737-57A1249, Revision 1, describes more rework instructions than does Boeing Service Bulletin 737-57-1065. Airplanes reworked according to Boeing Service Bulletin 737-57-1065 would require additional rework according to this proposed AD and Boeing Service Bulletin 737-57A1249, Revision 1.

Actions Since Issuance of NPRM

The NPRM listed certain Boeing Model 737-100, -200, and -200C series airplanes in its applicability statement. Since the issuance of the NPRM, the FAA has received a report of similar cracking in the area addressed by the NPRM on a Boeing Model 737-300 series airplane. The interface between the inboard track of each outboard flap and the rear spar on the subject Model 737-300 series airplane had been modified according to procedures similar to those identified as optional terminating action in the NPRM. Other Model 737-300, -400, and -500 series airplanes also have been similarly modified. Because of this report, the FAA finds that certain Model 737-300, -400, and -500 series airplanes—in addition to the Model 737-100, -200, and -200C series airplanes identified in the NPRM—may be subject to the unsafe condition addressed by this proposed AD. Therefore, the applicability statement of this supplemental NPRM lists all of these airplanes.

In addition, Boeing Service Bulletin 737-57A1249, Revision 1, states that no more work is necessary following the rework of the flap track described in that service bulletin. Because of the report of cracking on the Model 737-300 series airplane described above, the FAA finds that rework according to Boeing Service Bulletin 737-57A1249, Revision 1, may not ensure an adequate level of safety for the service life of the airplane. Therefore, this supplemental NPRM proposes to require additional repetitive inspections following the rework or the modification equivalent to the rework that was done during production on certain airplanes.

Comments

Due consideration has been given to the comments received in response to the NPRM. Certain comments have resulted in changes to the proposal, and those comments are addressed below.

Request To Clarify Airplanes Not Affected By Proposed Rule

One commenter requests that the FAA revise the proposed rule to clarify that certain airplanes are not subject to the proposed actions. The commenter states that airplanes having line numbers (L/N) 1032 through 1585 on which new flap tracks were installed according to Boeing Service Bulletin 737-57-1203, dated November 15, 1990, do not need to have flap tracks replaced as specified in the proposed rule. The commenter states that new flap tracks installed according to that service bulletin have the new aluminum anti-fret strip that this proposed AD would require and meet all requirements of the proposed rule.

The FAA concurs with the commenter's request. The applicability of this supplemental NPRM has been revised to exclude airplanes on which new flap tracks were installed according to Boeing Service Bulletin 737-57-1203.

Request To Require Repetitive Inspections for All Airplanes

One commenter requests that repetitive inspections for cracking be required for all airplanes. For airplanes having L/Ns 870 through 1585 inclusive on which replacement flap tracks are installed, paragraph (c) of the NPRM states that no further action is required if no corrosion or cracking is found during the initial inspection. The commenter states that one-time visual and HFEC inspections may not be sufficient to ensure that any crack is found in a timely manner.

The FAA concurs with the commenter's request, and paragraph (c) of the NPRM has not been included in this supplemental NPRM. This supplemental NPRM proposes to require inspections and eventual rework or replacement of flap tracks for all airplanes with L/Ns 1 through 869 inclusive and airplanes with L/Ns 870 through 1585 inclusive on which the original flap tracks have been replaced with certain flap tracks. As stated above, this supplemental NPRM also proposes to require post-rework repetitive inspections for all airplanes identified in the applicability statement of this document.

Request To Clarify Need for Additional Work on Certain Airplanes

One commenter, the manufacturer, requests that the proposed AD be revised to make it clear that airplanes modified according to Boeing Service Bulletin 737-57-1065, Revision 3, require additional work according to Boeing Service Bulletin 737-57A1249. The commenter states that this change is necessary because Boeing Service Bulletin 737-57-1065, Revision 3, was not intended to address the specific unsafe condition identified in the proposed AD.

The FAA concurs with the commenter's request and has included appropriate statements in the “Explanation of New Service Information” section of the preamble of this supplemental NPRM. Also, a new “Note 2” has been added to the body of this proposed AD to state that airplanes modified according to Boeing Service Bulletin 737-57-1065 are subject to additional work as described in this AD and in Boeing Service Bulletin 737-57A1249, Revision 1.

Request To Clarify Terminology

One commenter requests various changes to language used in the NPRM. The changes recommended by the commenter include:

• Refer to “anti-fret strip” instead of “rub strip” in the “Discussion” and “Explanation of Relevant Service Information” sections of the proposed AD.
• Clarify the procedures involved in the rework as described in the “Explanation of Relevant Service Information” section of the proposed AD.
• Clarify the cause of the unsafe condition by revising the sentence in the “Discussion” section of the proposed AD that reads, “inadequate clamp-up of the attachment bolts can make the area where the flap track attaches to the rear spar more vulnerable to moisture absorption and, consequently, to corrosion” to read, “insufficient clamp-up of the attachment bolts can cause damage to the attachment seals, tapered shim, anti-fret strip, and protective finishes, and make the area where the flap track attaches to the rear spar more vulnerable to moisture absorption and, consequently, to corrosion.”
• Identify the area affected by cracking as “the upper flange of the inboard track of each/the outboard flap at the rear spar attachment” in the “Discussion” and “Explanation of Requirements of Proposed Rule” sections of the preamble, and in the statement of unsafe condition in the body of the proposed AD.

The FAA concurs with the intent of the commenter's request. Though some of the specific sections of the preamble referenced by the commenter are not repeated in this supplemental NPRM, the changes suggested by the commenter have been made in this supplemental NPRM wherever appropriate.

Explanation of New Requirements of Proposal

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, for certain airplanes, new repetitive inspections for discrepancies (including corrosion, or missing, damaged, or migrated anti-fret strips and tapered shims) of the rear spar attachments and cracks in the upper flange of the inboard track at the rear spar attachment of each outboard flap. For certain airplanes, the proposed AD also would require eventual rework of the flap track assembly and rear spar attachments, including replacement of the flap track with a new track, if necessary. For all airplanes, this action would require post-rework repetitive inspections for cracks in the upper flange of the inboard flap tracks at the rear spar attachments, and corrective action, if necessary. The actions would be required to be accomplished according to Boeing Service Bulletin 737-57A1249, Revision 1, except as discussed below.

Differences Between Supplemental NPRM and Service Bulletin

This supplemental NPRM differs from Boeing Service Bulletin 737-57A1249, Revision 1, in the following ways:

• Though the service bulletin states compliance times in terms of flight cycles and calendar time, this proposed AD states compliance times only in calendar time. The FAA finds it appropriate to state compliance times for the requirements of this proposed AD only in calendar time because corrosion cracking is a function of time, not flight cycles.
• The airplane manufacturer recommends that the actions in the service bulletin be accomplished on airplanes with 20,000 flight cycles or more, or 10 years of service. The FAA finds that, as of the effective date of this AD, all airplanes identified in paragraph (a) of this proposed AD will have been in service for more than 10 years since their date of manufacture. Therefore, this supplemental NPRM does not refer to this threshold in the compliance times for paragraphs (a), (b), and (c) of this AD.
• Operators also should note that, though the service bulletin specifies that the manufacturer may be contacted for disposition of certain repair conditions, this proposed AD would require the repair of those conditions to be accomplished according to a method approved by the FAA, or according to 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.

Conclusion

Since this change expands the scope of the originally proposed rule, the FAA has determined that it is necessary to reopen the comment period to provide additional opportunity for public comment.

Cost Impact

There are approximately 2,890 airplanes of the affected design in the worldwide fleet. The FAA estimates that 1,100 airplanes of U.S. registry would be affected by this proposed AD.

It would take approximately 4 work hours per airplane to accomplish the proposed inspections, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the proposed inspections on U.S. operators is estimated to be $264,000, or $240 per airplane, per inspection cycle.

It would take approximately 12 work hours per airplane to accomplish the proposed rework, at an average labor rate of $60 per work hour. Required parts would cost approximately $532. Based on these figures, the cost impact of the rework proposed by this AD on U.S. operators is estimated to be $1,377,200, or $1,252 per airplane.

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 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 99-NM-21-AD.

Applicability: Model 737-100, -200, -200C, -300, -400, and -500 series airplanes; certificated in any category; EXCEPT airplanes on which any replacement flap tracks were installed according to Boeing Service Bulletin 737-57-1203, dated November 15, 1990, or production equivalent.

Note 1:

This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been otherwise 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 (f) 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.

Note 2:

Airplanes modified according to Boeing Service Bulletin 737-57-1065 are subject to additional work as described in this AD and in Boeing Service Bulletin 737-57A1249, Revision 1, dated June 1, 2000.

To find and fix discrepancies of the inboard tracks of the outboard flaps, which could result in loss of the outboard trailing edge flaps and consequent reduced controllability of the airplane, accomplish the following:

Initial Inspections

(a) For airplanes with line numbers (L/N) 1 through 869 inclusive, and airplanes with L/Ns 870 through 1585 on which the original flap tracks have been replaced with certain tracks as specified in Boeing Service Bulletin 737-57A1249, Revision 1, including Appendix A, dated June 1, 2000: Within 6 months after the effective date of this AD, whichever occurs later, accomplish the requirements of paragraphs (a)(1) and (a)(2) of this AD, according to Boeing Service Bulletin 737-57A1249, Revision 1, including Appendix A, dated June 1, 2000.

(1) Perform a detailed visual inspection for discrepancies (e.g., corrosion, or missing, damaged, or migrated anti-fret strips and tapered shims) of the rear spar attachments of the flap tracks.

(2) Perform detailed visual, high frequency eddy current (HFEC), and ultrasonic inspections for cracking in the upper flange of the inboard track of each outboard flap at the rear spar attachments.

Note 3:

Inspections and rework accomplished according to Boeing Alert Service Bulletin 737-57A1249, including Appendix A, dated December 16, 1999, is considered acceptable for compliance with the applicable action specified in this AD.

Note 4:

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.”

Repetitive Inspections

(b) For airplanes subject to paragraph (a) of this AD: If no discrepancy is found during any inspection required by paragraph (a) of this AD, thereafter, repeat the inspections specified in paragraph (a) of this AD at intervals not to exceed 9 months, until the actions required by paragraph (c) of this AD have been accomplished.

Rework

(c) For airplanes subject to paragraph (a) of this AD: At the applicable time specified in paragraph (c)(1) or (c)(2) of this AD, accomplish rework of the flap track assembly and aft flap track attachments (including removal of the flap track; a detailed visual inspection for a missing, damaged, or migrated anti-fret strip and tapered shim of the rear spar attachments of the flap track; replacement of the anti-fret strip with a new aluminum anti-fret strip (or installation of an aluminum strip if no strip is installed), as applicable; replacement of the tapered shim with a new shim (or installation of a shim if no shim is installed); eddy current and ultrasonic inspections for fatigue cracking of the flap tracks; a detailed visual inspection for corrosion of the flap tracks; and rework of attachment holes), including replacement of the flap tracks, as applicable, by accomplishing all actions specified in part II of the Accomplishment Instructions of Boeing Service Bulletin 737-57A1249, Revision 1, including Appendix A, dated June 1, 2000. Do these actions according to that service bulletin, except as provided by paragraph (e) of this AD. Accomplishment of the actions required by this paragraph constitutes terminating action for the repetitive inspections required by paragraph (b) of this AD.

(1) If no discrepancy is found during any inspection required by paragraph (a) or (b) of this AD: Do the rework within 24 months after the effective date of this AD, whichever occurs later.

(2) If any discrepancy is found during any inspection required by paragraph (a) or (b) of this AD: Do the rework prior to further flight.

Repetitive Inspections

(d) For all airplanes: At the applicable time specified in paragraph (d)(1) or (d)(2) of this AD, and thereafter at least every 24 months, perform detailed visual, HFEC, and ultrasonic inspections for cracking in the upper flange of the inboard track of each outboard flap at the rear spar attachments according to Part II of the Accomplishment Instructions of Boeing Service Bulletin 737-57A1249, Revision 1, including Appendix A, dated June 1, 2000.

(1) For airplanes subject to paragraph (c) of this AD, do the inspections within 10 years after accomplishment of the rework according to paragraph (c) of this AD.

(2) For airplanes other than those identified in paragraph (d)(1) of this AD, do the inspections within 10 years since the airplane's date of manufacture, or within 6 months after the effective date of this AD, whichever occurs later.

Repair Instructions and Exception to Procedures in Service Information

(e) If any discrepancy is found during any action required by paragraphs (a), (b), or (c) of this AD, and the service bulletin specifies to contact Boeing for appropriate action; OR if any discrepancy is found during inspections according to paragraph (d) of this AD: Prior to further flight, repair according to a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA; or according to 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 approval letter must specifically reference this AD.

Alternative Methods of Compliance

(f) 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 5:

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

(g) 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 July 26, 2001.

Vi L. Lipski,

Manager, Transport Airplane Directorate, Aircraft Certification Service.