E8-20102. Airworthiness Directives; Boeing Model 737-100, -200, -200C, -300, -400, and -500 Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Supplemental notice of proposed rulemaking (NPRM); reopening of comment period.

SUMMARY:

We are revising an earlier proposed airworthiness directive (AD) for certain Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. The original NPRM would have required doing repetitive internal eddy current and detailed inspections to detect cracked stringer tie clips; measuring the fastener spacing and the edge margin if applicable, and doing applicable corrective and related investigative actions. As a temporary alternative to doing the actions described previously, the original NPRM would have required repetitive inspections of the skin and lap joints for cracks and evidence of overload resulting from cracked stringer tie clips, and applicable corrective actions if necessary. The original NPRM resulted from a report of several cracked stringer tie clips. This action revises the original NPRM by including repetitive external eddy current sliding probe inspections of the lap joints for cracks and evidence of overload resulting from cracked stringer tie clips. We are proposing this supplemental NPRM to detect and correct multiple adjacent cracked stringer tie clips and damaged skin and frames, which could lead to the skin and frame structure developing cracks and consequent decompression of the airplane.

DATES:

We must receive comments on this supplemental NPRM by September 23, 2008.

ADDRESSES:

You may send comments by any of the following methods:

• Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
• Fax: [phone].
• Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590.
• Hand Delivery: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

For service information identified in this AD, contact Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207.

Examining the AD Docket

You may examine the AD docket on the Internet at http://www.regulations.gov; or in person at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this proposed AD, the regulatory evaluation, any comments received, and other information. The street address for the Docket Office (telephone [phone]) is in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.

FOR FURTHER INFORMATION CONTACT:

Wayne Lockett, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone [phone]; fax [phone].

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to send any written relevant data, views, or arguments about this proposed AD. Send your comments to an address listed under the ADDRESSES section. Include “Docket No. FAA-2007-29255; Directorate Identifier 2007-NM-085-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of this proposed AD. We will consider all comments received by the closing date and may amend this proposed AD because of those comments.

We will post all comments we receive, without change, to http://www.regulations.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact we receive about this proposed AD.

Discussion

We issued a notice of proposed rulemaking (NPRM) (the “original NPRM”) to amend 14 CFR part 39 to include an airworthiness directive (AD) that would apply to certain Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. That original NPRM was published in the Federal Register on September 20, 2007 (72 FR 53706). That original NPRM proposed to require doing repetitive internal eddy current and detailed inspections to detect cracked stringer tie clips; measuring the fastener spacing and the edge margin if applicable; and doing applicable corrective and related investigative actions. As a temporary alternative to doing the actions described previously, that original NPRM proposed to require repetitive external general visual inspections of the skin and lap joints for cracks and evidence of overload resulting from cracked stringer tie clips, and applicable corrective actions if necessary.

Comments

We gave the public the opportunity to participate in developing this AD. We considered the comments received from the four commenters.

Requests To Revise Grace Period for Accomplishing Inspections A and B

US Airways requests that, for certain airplane configurations, the grace period for accomplishing the initial inspections specified in paragraph (g) of the original NPRM (Inspection A) be extended from 2 years to 4 years. KLM requests that the grace period of Inspection A be extended to 8 years, and that the intervals for accomplishing the temporary alternative inspection specified in paragraph (h) of the original NPRM (Inspection B) be reduced.

US Airways states that it has been successfully inspecting the same area for corrosion and other damage per the Corrosion Prevention and Control Program (CPCP), as required by AD 90-25-01, amendment 39-6789 (55 FR 49263, November 27, 1990). US Airways states that the compliance time should be extended for operators accomplishing the CPCP. US Airways and KLM state extending the compliance time for accomplishing Inspection A would allow operators to better schedule that inspection, and thus would limit the economic impact. US Airways also states that temporary alternative inspections specified in paragraph (h) of the original NPRM (Inspection B) are not as desirable as Inspection A. US Airways believes Inspection B would increase the risk of damage to airplanes due to operators' need to use various lift equipment to reach the inspection area.

We do not agree with the commenters' request to extend the compliance time specified in paragraph (g) of the supplemental NPRM (Inspection A) or to reduce the compliance time specified in paragraph (h) of the supplemental NPRM (Inspection B). We have determined that the visual inspections required by AD 90-25-01 do not detect multiple adjacent cracks at stringer tie clips, which is the identified unsafe condition of this supplemental NPRM. The CPCP inspections cited do not focus on the areas of affected stringer tie clips. In developing an appropriate compliance time for this supplemental NPRM, we considered not only the degree of urgency associated with addressing the identified unsafe condition, but the practical aspect of incorporating the proposed inspections into affected operators' maintenance schedules in a timely manner. Further, deferral of Inspection A for multiple clip failures does not provide an acceptable level of safety. In light of these items, we have determined that the applicable compliance times identified in paragraphs (g) and (h) of the supplemental NPRM are appropriate. However, paragraph (o) of the supplemental NPRM provides affected operators the opportunity to apply for an adjustment of the compliance time if the operator also presents data that justify the adjustment.

Requests To Clarify Inspection B

The Air Transport Association (ATA), on behalf of one of its members, United Airlines, and Boeing request that paragraph (h) of the NPRM be clarified as to which affected airplanes the temporary alternative inspections specified in paragraph (h) of the original NPRM (Inspection B) may be done on. The commenters state that a note in the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-53-1268, dated August 25, 2006 (referred to as the appropriate source of service information for doing the proposed actions), limits Inspection B to airplanes having stringer tie clips replaced in accordance with Boeing Service Bulletin 737-53-1085, Revision 1, dated May 10, 1990. The commenters note that the AD does not have such a limitation.

We agree with the commenters that clarification is necessary. Paragraph (h) of the supplemental NPRM specifies to do all “applicable” actions in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-53-1268. As noted by the commenters, a note in the Accomplishment Instructions states, “The Option B Inspection is not allowed on airplanes that have not accomplished terminating action of replacing the stringer tie clips as given in Service Bulletin 737-53-1085.” However, the note does not explain that Boeing Service Bulletin 737-53-1085 affects only airplanes having line numbers 1 through 1000 inclusive. Without such an explanation, operators could misinterpret that paragraph (h) of the supplemental NPRM may be done on airplanes having line numbers 1001 and subsequent, which are also subject to the proposed actions of this supplemental NPRM. Therefore, we have added Note 3 to this supplemental NPRM to clarify this point.

Boeing also requests that the first sentence of paragraph (h) of the NPRM be revised to include eddy current inspections of the lap joints. Boeing states that, for Inspection B, Boeing Special Attention Service Bulletin 737-53-1268 specifies eddy current inspections of the lap joints.

We agree. It was our intent that the proposed inspections align with those specified in Boeing Special Attention Service Bulletin 737-53-1268. Therefore, we have revised paragraph (h) of the supplemental NPRM accordingly.

Request To Clarify Unsafe Condition

Boeing requests that, for clarification purposes, the unsafe condition throughout the original NPRM be revised from “* * * multiple cracked stringer tie clips * * *.” to “* * * multiple adjacent cracked stringer tie clips * * *.” Boeing states that the safety concern is when there are multiple “adjacent” stringer tie clips (three or more) that are cracked.

We agree and have revised the supplemental NPRM accordingly.

Request To Clarify Relevant Service Information Section

Boeing requests several editorial changes to the Relevant Service Information section of the original NPRM for clarification purposes.

We partially agree. We acknowledge that Boeing's suggested changes to that section would further clarify the information specified in the service bulletin. However, the Relevant Service Information section of the original NRPM does not reappear in the supplemental NPRM. Therefore, we have made no change to this supplemental NPRM in this regard.

Request To Revise Work-Hour Estimate

Boeing requests that the work hours for Inspection A in the Costs of Compliance section of the original NPRM be revised from between 40 and 103 to between 253 and 307. Boeing states that Inspection A requires internal access, which requires many more hours than that shown in the Estimated Costs table.

We do not agree. The Costs of Compliance section describes only the direct costs of the specific actions proposed by this supplemental NPRM. The estimated work hours represent the time necessary to perform only the actions actually proposed by this supplemental NPRM. We recognize that, in doing the actions required by an AD, operators might incur incidental costs in addition to the direct costs. The cost analysis in AD rulemaking actions, however, typically does not include incidental costs such as the time required to gain access and close up, time necessary for planning, or time necessitated by other administrative actions. Those incidental costs, which might vary significantly among operators, are almost impossible to calculate. Therefore, we have made no change to the supplemental NPRM in this regard.

Clarification of Unsafe Condition

The Summary section and paragraph (d) of the NPRM state, “We are proposing this supplemental NPRM to prevent multiple cracked stringer tie clips and damaged skin and frames * * *” For clarification purposes, we have changed the phrase “to prevent” to “to detect and correct” in that section and paragraph of this supplemental NPRM.

FAA's Determination and Proposed Requirements of the Supplemental NPRM

We are proposing this supplemental NPRM because we evaluated all pertinent information and determined an unsafe condition exists and is likely to exist or develop on other products of the same type design. Certain changes described above expand the scope of the original NPRM. As a result, we have determined that it is necessary to reopen the comment period to provide additional opportunity for the public to comment on this supplemental NPRM.

Costs of Compliance

We estimate that this proposed AD would affect 787 airplanes of U.S. registry. The following table provides the estimated costs for U.S. operators to comply with this proposed AD.

Estimated Costs

Action	Work hours 1	Average labor rate per hour	Cost per airplane 1	Number of U.S.- registered airplanes	Fleet cost 1
Inspection A	Between 40 and 103	$80	Between $3,200 and $8,240, per inspection cycle	787	Between $2,518,400 and $6,484,880, per inspection cycle.
Inspection B (temporary alternative to Inspection A)	Between 2 and 109	80	Between $160 and $8,720	787	Between $125,920 and $6,862,640, per inspection cycle.
1 Depending on the airplane configuration.

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. “Subtitle VII: Aviation Programs,” describes in more detail the scope of the Agency's authority.

We are issuing this rulemaking under the authority described in “Subtitle VII, Part A, Subpart III, Section 44701: General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

Regulatory Findings

We determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD 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.

For the reasons discussed above, I certify 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. 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.

You can find our regulatory evaluation and the estimated costs of compliance in the AD Docket.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Safety

The Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 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. The FAA amends § 39.13 by adding the following new AD:

Boeing: Docket No. FAA-2007-29255; Directorate Identifier 2007-NM-085-AD.

Comments Due Date

(a) We must receive comments by September 23, 2008.

Affected ADs

(b) AD 93-08-04, amendment 39-8551.

Applicability

(c) This AD applies to Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes, certificated in any category; as identified in Boeing Special Attention Service Bulletin 737-53-1268, dated August 25, 2006.

Unsafe Condition

(d) This AD results from a report of several cracked stringer tie clips. We are issuing this AD to detect and correct multiple adjacent cracked stringer tie clips and damaged skin and frames, which could lead to the skin and frame structure developing cracks and consequent decompression of the airplane.

Compliance

(e) You are responsible for having the actions required by this AD performed within the compliance times specified, unless the actions have already been done.

Service Bulletin References

(f) The term “the service bulletin,” as used in this AD, means the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-53-1268, dated August 25, 2006.

Inspection A: Required Internal Inspections, Applicable Corrective and Related Investigative Actions, and Measurement

(g) Do repetitive internal eddy current and detailed inspections to detect cracked stringer tie clips; measure the fastener spacing and the edge margin if applicable; and do applicable corrective and related investigative actions. Do all applicable actions at the applicable compliance times and repeat intervals identified in Tables 2 through 8 inclusive of paragraph 1.E., “Compliance,” of the service bulletin; except as provided by paragraphs (i) through (l) of this AD. Do all applicable actions in accordance with the Accomplishment Instructions of the service bulletin, except as provided by paragraph (m) of this AD.

Note 1:

The service bulletin refers to Boeing Service Bulletin 737-53A1177, Revision 6, dated May 31, 2001, as an additional source of service information for doing an internal eddy current inspection of the lap joint for certain airplane configurations.

Inspection B: Temporary Alternative External Inspections and Corrective Actions

(h) As a temporary alternative to doing the actions required by paragraph (g) of this AD, do repetitive external general visual inspections of the skin and lap joints and repetitive external eddy current sliding probe inspections of the lap joints for cracks and evidence of overload resulting from cracked stringer tie clips, and applicable corrective actions if necessary. Do all applicable actions at the applicable compliance times and repeat intervals identified in Tables 9 through 12 inclusive of paragraph 1.E., “Compliance,” of the service bulletin, but not to exceed the flight cycles in the “Inspection Period Allowed” column of the tables; except as provided by paragraphs (i) and (l) of this AD. Do all applicable actions in accordance with the Accomplishment Instructions of the service bulletin, except as provided by paragraph (m) of this AD.

Note 2:

The eddy current inspection along the stringer tie clip radius to detect damage and replacement, as applicable, specified in paragraph 3.B.5. of the Accomplishment Instructions of the service bulletin are not required by this AD. The actions are optional and can be done in addition to and at the same time as the actions required by paragraph (g) of this AD.

Note 3:

Inspection B may be used on affected airplanes having line numbers 1 through 1000 inclusive on which the terminating action (i.e., replacement of stringer tie clips) specified in Boeing Service Bulletin 737-53-1085, Revision 1, dated May 10, 1990, has been done; and on affected airplanes having line numbers 1001 and subsequent. The service bulletin contains a similar note.

Exceptions to Service Information

(i) Where the service bulletin specifies a compliance time after the date of the service bulletin, this AD requires compliance within the specified compliance time after the effective date of this AD.

(j) For Model 737-100, -200, and -200C series airplanes, on which Boeing Service Bulletin 737-53-1085, Revision 1, dated May 10, 1990, has not been done in accordance with AD 93-08-04: As of the effective date of this AD, do the applicable inspections from station (STA) 559 to STA 887 in accordance with paragraph (g) of this AD, at the applicable compliance times specified in paragraph (b) of AD 93-08-04.

(k) In the first row of Tables 5 and 6 of paragraph 1.E., “Compliance,” of the service bulletin, where the service bulletin specifies a compliance time of before 25,000 total airplane flight cycles, this AD requires a compliance time of before the accumulation of 25,000 total flight cycles, or within 2 years after the effective date of this AD, whichever occurs later.

(l) Where the service bulletin specifies no starting point (e.g., “after the date on the service bulletin”) for a grace period, this AD requires compliance within the specified grace period after the effective date of this AD.

(m) Where the service bulletin specifies to contact Boeing for appropriate action: Before further flight, repair the discrepancy using a method approved in accordance with the procedures specified in paragraph (o) of this AD.

Certain Actions End Certain Requirements of AD 93-08-04

(n) Accomplishment of the internal eddy current and detailed inspections for STA 559 to STA 887 in accordance with paragraph (g) of this AD constitutes compliance with the inspections required by paragraph (a) of AD 93-08-04, as it pertains to Boeing Service Bulletin 737-53-1085, Revision 1, dated May 10, 1990. Accomplishment of the internal eddy current and detailed inspections does not terminate the remaining requirements of AD 93-08-04, as it applies to other service bulletins. Operators are required to continue to inspect and/or modify per the other service bulletins listed in that AD.

Alternative Methods of Compliance (AMOCs)

(o)(1) The Manager, Seattle Aircraft Certification Office (ACO), FAA, ATTN: Wayne Lockett, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle ACO, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone [phone]; fax [phone]; has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19.

(2) To request a different method of compliance or a different compliance time for this AD, follow the procedures in 14 CFR 39.19. Before using any approved AMOC on any airplane to which the AMOC applies, notify your appropriate principal inspector (PI) in the FAA Flight Standards District Office (FSDO), or lacking a PI, your local FSDO.

(3) An AMOC that provides an acceptable level of safety may be used for any repair required by this AD, if it is approved by an Authorized Representative for the Boeing Commercial Airplanes Delegation Option Authorization Organization who has been authorized by the Manager, Seattle ACO, to make those findings. For a repair method to be approved, the repair must meet the certification basis of the airplane, and the approval must specifically refer to this AD.

Issued in Renton, Washington, on August 20, 2008.

Kevin Hull,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.