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###### Department of Transportation

###### Federal Aviation Administration 

          - 14 CFR Part 39 
          - [Docket No. 2000-NM-327-AD] 
          - RIN 2120-AA64 

# AGENCY:

Federal Aviation Administration, DOT. 

# ACTION:

Notice of proposed rulemaking (NPRM). 

# SUMMARY:

                        This document proposes the adoption of a new airworthiness                               ( print page 10391)                            directive (AD) that is applicable to all Boeing Model 737-100 and -200 series airplanes. This proposal would require repetitive inspections to find fatigue cracking in the main deck floor beams located at certain body stations, and repair, if necessary. This proposal also provides for optional terminating action for the repetitive inspections. This action is necessary to prevent failure of the main deck floor beams at certain body stations due to fatigue cracking, which could result in rapid decompression and consequent reduced controllability of the airplane. This action is intended to address the identified unsafe condition.                     

# DATES:

Comments must be received by April 2, 2001. 

# ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-327-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 (425) 227-1232. Comments may also be sent via the Internet using the following address: 9-anm-nprmcomment@faa.gov. Comments sent via fax or the Internet must contain “Docket No. 2000-NM-327-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 (425) 227-1221; fax (425) 227-1181. 

# 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-327-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-327-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. 

## Discussion 

The FAA has received reports from the manufacturer indicating several operators have found cracking in the body buttock line (BBL) 0.07 floor beams. On airplanes having between 27,000 and 55,000 total flight cycles, cracks were found in the upper chord at body station (BS) 663. On airplanes having between 31,000 and 51,000 total flight cycles, cracks were found in the web at BS 663. On airplanes having between 18,000 and 54,000 total flight cycles, cracks were found in the lower chord at BS 727. On airplanes having between 23,000 and 39,000 total flight cycles, cracks were found in the web at BS 706 through 711. Investigation revealed that the cracks were caused by fatigue resulting from pressurization flexure. Failure of the main deck floor beams at certain body stations due to fatigue cracking could result in rapid decompression and consequent reduced controllability of the airplane. 

## Explanation of Relevant Service Information 

The FAA has reviewed and approved Boeing Service Bulletin 737-57-1210, dated April 4, 1991, which describes procedures for repetitive visual inspections of the main deck floor beams located between BS 650 and BS 730, around BS 710 and BS 727, and at BS 650 through 675, to find cracking; and repair of any cracking found. If no cracking is found after doing the visual inspection, the service bulletin provides an option for a one-time eddy current inspection of the fastener holes. If no cracking is found during the eddy current inspection, doing the modification (change) of the applicable floor beams would end the repetitive visual inspections for that area. 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. 

## Difference Between Service Bulletin and This Proposed Rule 

Operators should note that, although the service bulletin specifies that the manufacturer may be contacted for disposition of certain repair conditions, this proposed AD requires the repair of those conditions to be done 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. 

Operators also should note that the FAA has determined that the repetitive inspections proposed by this AD can be allowed to continue instead of doing a terminating action. In making this determination, the FAA considers that, in this case, long-term continued operational safety will be adequately assured by doing the repetitive inspections to find cracking before it represents a hazard to the airplane. 

## Cost Impact 

                    There are approximately 935 airplanes of the affected design in the                           ( print page 10392)                        worldwide fleet. The FAA estimates that 340 airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately 8 work hours per airplane to do the proposed inspection, 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 $163,200, or $480 per airplane.                 

The cost impact figure discussed above is based on assumptions that no operator has yet done any of the proposed requirements of this AD action, and that no operator would do 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 do 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. 

Should an operator elect to do the optional terminating action rather than continue the repetitive inspections, it would take approximately 96 work hours per airplane to do the change, at an average labor rate of $60 per work hour. Required parts would cost between $218 and $1,426 per airplane. Based on these figures, the cost impact of this optional terminating action is estimated to be between $5,978 and $7,186 per airplane. 

## 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 

2. Section 39.13 is amended by adding the following new airworthiness directive: 

**Boeing:**                                 Docket 2000-NM-327-AD.                            

*Applicability:*                                All Model 737-100 and -200 series airplanes, 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 per 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 failure of the main deck floor beams at certain body stations (BS) due to fatigue cracking, which could result in rapid decompression and consequent reduced controllability of the airplane, do the following: 

## Inspections 

(a) Before the accumulation of 20,000 total flight cycles, or within 6,000 flight cycles after the effective date of this AD, whichever occurs later: Do a detailed visual inspection to find cracking of the main deck floor beams [body buttock line (BBL) 0.07] located between BS 650 and BS 730, per the Accomplishment Instructions of Boeing Service Bulletin 737-57-1210, dated April 4, 1991. If no cracking is found, do the requirements in paragraph (a)(1) or (a)(2) of this AD at the applicable times specified. 

# 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 find 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) If no cracking is found around BS 710 (Figure 1) or BS 727 (Figure 2), do the requirements in either paragraph (a)(1)(i) or (a)(1)(ii) of this AD. 

(i) Repeat the detailed visual inspection at intervals not to exceed 6,000 flight cycles until accomplishment of the change specified in paragraph (c) of this AD. Or 

(ii) Before further flight, do a one-time eddy current inspection for cracking of the fastener holes. If no cracking is found, before further flight, install the change at BS 710 (Figure 6) or BS 727 (Figure 7), as applicable, per the Accomplishment Instructions of the service bulletin. Doing the change ends the repetitive inspections for that area. 

(2) If no cracking is found at BS 650 through BS 675 (Figure 8), do the requirements in either paragraph (a)(2)(i) or (a)(2)(ii) of this AD. 

(i) Repeat the detailed visual inspection at intervals not to exceed 3,000 flight cycles until accomplishment of the change specified in paragraph (c) of this AD. Or 

(ii) Before further flight, do a one-time eddy current inspection for cracking of the fastener holes. If no cracking is found, before further flight, install the change at BS 663 (Figure 9) per the Accomplishment Instructions of the service bulletin. Doing the change ends the repetitive inspections for that area. 

## Repair 

(b) If any cracking is found during any inspection required by paragraph (a) of this AD, before further flight, either do the repair per the Accomplishment Instructions of Boeing Service Bulletin 737-57-1210, dated April 4, 1991, or do the change specified in paragraph (c) of this AD. Where the service bulletin specifies to contact Boeing for repair instructions: Before further flight, repair 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 FAA 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. 

## Optional Terminating Action 

(c) Accomplishment of the main deck floor beam change in the applicable areas [BS 710 (Figure 6), BS 727 (Figure 7), or BS 650 through 675 (Figure 9)], specified in the Accomplishment Instructions of Boeing Service Bulletin 737-57-1210, dated April 4, 1991, ends the repetitive inspections for that area. 

## 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                                       ( print page 10393)                                    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 Permit 

(e) Special flight permits may be issued per 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 done. 

Issued in Renton, Washington, on February 9, 2001. 

Vi L. Lipski, 

Manager, Transport Airplane Directorate, Aircraft Certification Service.

[FR Doc. 01-3858 Filed 2-14-01; 8:45 am] 

BILLING CODE 4910-13-U