E7-18049. Airworthiness Directives; Boeing Model 737-100, -200, -200C, -300, -400, and -500 Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), Department of Transportation (DOT).

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. This proposed AD would require repetitive inspections to detect cracking of the body station 303.9 frame, and corrective action if necessary. This proposed AD also provides for optional terminating action for the repetitive inspections. This proposed AD results from reports of cracks found at the cutout in the web of body station frame 303.9 inboard of stringer 16L. We are proposing this AD to detect and correct such cracking, which could prevent the left forward entry door from sealing correctly, and could cause in-flight decompression of the airplane.

DATES:

We must receive comments on this proposed AD by October 29, 2007.

ADDRESSES:

Use one of the following addresses to submit comments on this proposed AD.

• DOT Docket Web site: Go to http://dms.dot.gov and follow the instructions for sending your comments electronically.
• Government-wide rulemaking Web site: Go to http://www.regulations.gov and follow the instructions for sending your comments electronically.
• 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.
• Fax: [phone].
• Hand Delivery: Room W12-140 on the ground floor of the West Building, 1200 New Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

Contact Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207, for the service information identified in this proposed AD.

FOR FURTHER INFORMATION CONTACT:

Howard Hall, 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 submit any relevant written data, views, or arguments regarding this proposed AD. Send your comments to an address listed in the ADDRESSES section. Include the docket number “FAA-2007-29174; Directorate Identifier 2007-NM-125-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the proposed AD. We will consider all comments received by the closing date and may amend the proposed AD in light of those comments.

We will post all comments we receive, without change, to http://dms.dot.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this proposed AD. Using the search function of that web site, anyone can find and read the comments in any of our dockets, including the name of the individual who sent the comment (or signed the comment on behalf of an association, business, labor union, etc.). You may review DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you may visit http://dms.dot.gov.

Examining the Docket

You may examine the AD docket on the Internet at http://dms.dot.gov, or in person at the Docket Operations office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Operations office (telephone [phone]) is located on the ground floor of the West Building at the DOT street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after the Docket Management System receives them.

Discussion

We have received reports of cracks found at the cutout in the web of the body station 303.9 frame inboard of stringer 16L on seven Boeing Model 737 “classic” airplanes. The cracks were found on airplanes that had accumulated between 37,562 and 64,000 total flight cycles. Such cracking, if not corrected, could prevent the left forward entry door from sealing correctly, and could cause in-flight decompression of the airplane.

Relevant Service Information

We have reviewed two service bulletins related to this action. The service bulletins are similar but affect different groups of airplanes.

Boeing Alert Service Bulletin 737-53A1188, Revision 2, dated May 9, 2007, for certain Model 737-300, -400, and -500 series airplanes, describes the following actions:

• Repetitive high-frequency eddy current (HFEC) and detailed inspections to detect cracking in the station 303.9 web and doubler around the cutouts for door stop straps at stringers 15L and 16L.
• A repair/preventive change, which includes installing a new web, doubler, and stop fitting assemblies; changing the shape of the web cutout; and doing an eddy current inspection.

Service Bulletin 737-53A1188 specifies a threshold for the initial inspection of 10,000 total flight cycles and a grace period of 2,250 flight cycles.

Boeing Alert Service Bulletin 737-53A1197, dated August 25, 2006, for certain Model 737-100, -200, -200C, -300, -400, and -500 series airplanes, describes the following actions:

• Repetitive ultrasound inspections of the slot-shaped cutout in the web for the door stop strap at stringer 16L.
• Repetitive HFEC inspections of the web along the upper edge and lower edge of the doubler around the doorstop strap at stringer 16L.
• Repetitive detailed inspections of the web around the doubler for the cutout at stringer 16.
• A repair/preventive change, which involves installing a new web and doubler.

Service Bulletin 737-53A1197 specifies a threshold for the initial inspection of 30,000 total flight cycles and a grace period of 2,250 flight cycles.

For both service bulletins, a repair/preventive change eliminates the need for the repetitive inspections. For airplanes on which the repair/preventive change was previously done according to the original version or Revision 1 of Alert Service Bulletin 737-53A1188, replacing the existing kit with a new kit (in accordance with Revision 2) is necessary to eliminate the need for the repetitive inspections.

Accomplishing the actions specified in the service bulletins is intended to adequately address the unsafe condition.

FAA's Determination and Requirements of the Proposed AD

We have evaluated all pertinent information and identified an unsafe condition that is likely to exist or develop on other airplanes of this same type design. For this reason, we are proposing this AD, which would require accomplishing the actions specified in the service information described previously, except as discussed below.

Difference Between Proposed AD and Service Information

The service bulletins specify to contact the manufacturer for instructions on how to repair certain conditions, but this proposed AD would require repairing those conditions in one of the following ways:

• Using a method that we approve; or
• Using data that meet the certification basis of the airplane, and that have been approved by an Authorized Representative for the Boeing Commercial Airplanes Delegation Option Authorization Organization whom we have authorized to make those findings.

Costs of Compliance

There are about 2,765 airplanes of the affected design in the worldwide fleet. The following table provides the estimated costs, depending on airplane configuration, for U.S. operators to comply with this proposed AD.

Estimated Costs

Action	Work hours	Average labor rate per hour	Parts	Cost per airplane	Number of U.S.-registered airplanes	Fleet cost
Inspection	1 to 4	$80	None	$80 to $320, per inspection cycle	1,154	$92,320 to $369,280, per inspection cycle.
Repair/preventive change, if done	12 to 30	80	$564 to $2,236	$1,524 to $4,636	Up to 1,154	Up to $5,349,944.

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 have 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 that the 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.

We prepared a regulatory evaluation of the estimated costs to comply with this proposed AD and placed it in the AD docket. See the ADDRESSES section for a location to examine the regulatory evaluation.

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 Federal Aviation Administration (FAA) amends § 39.13 by adding the following new airworthiness directive (AD):

Boeing: Docket No. FAA-2007-29174; Directorate Identifier 2007-NM-125-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by October 29, 2007.

Affected ADs

(b) None.

Applicability

(c) This AD applies to the airplanes, certificated in any category, identified in Table 1 of this AD.

Table 1.—Applicability

Boeing model—	As identified in Boeing Alert Service Bulletin—
737-100, -200, and -200C series airplanes	737-53A1197, dated August 25, 2006.
737-300, -400, and -500 series airplanes	737-53A1188, Revision 2, dated May 9, 2007, or 737-53A1197, dated August 25, 2006.

Unsafe Condition

(d) This AD results from reports of cracks found at the cutout in the web of body station frame 303.9 inboard of stringer 16L. We are issuing this AD to detect and correct such cracking, which could prevent the left forward entry door from sealing correctly, and could cause in-flight 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.

Repetitive Inspections: Service Bulletin 737-53A1188

(f) For airplanes identified in Boeing Alert Service Bulletin 737-53A1188, Revision 2, dated May 9, 2007, including airplanes modified by the repair/preventive change specified in the original version, dated April 9, 1998, or Revision 1, dated March 18, 1999, of the service bulletin: Do detailed and high frequency eddy current (HFEC) inspections in the web and doubler around the slotted holes in the frame web at stringers 15L and 16L, in accordance with the Accomplishment Instructions of the service bulletin. Do the inspections at the applicable time specified in paragraph 1.E. of the service bulletin, except as provided by paragraph (h) of this AD. Do all applicable corrective actions before further flight in accordance with the service bulletin, except as provided by paragraph (i) of this AD. Repeat the inspections at intervals not to exceed 4,500 flight cycles until accomplishment of the repair/preventive change in accordance with the service bulletin, which terminates the repetitive inspection requirements. A repair/preventive change done in accordance with the original version or Revision 1 of the service bulletin does not terminate the repetitive inspections, but the repetitive inspections may be terminated after the existing kit is replaced with a new kit in accordance with Revision 2 of the service bulletin, paragraph 3.B., Part II, step 3, or Part III, step 3.

Repetitive Inspections: Service Bulletin 737-53A1197

(g) For airplanes identified in Boeing Alert Service Bulletin 737-53A1197, dated August 25, 2006: Do an ultrasound inspection of the slot-shaped cutout in the web for the door stop strap at stringer 16L, an HFEC inspection of the web along the upper and lower edges of the doubler around the doorstop strap at stringer 16L, and a detailed inspection of the web around the doubler for the cutout at stringer 16L, in accordance with the Accomplishment Instructions of the service bulletin. Do the inspections at the applicable time specified in paragraph 1.E. of the service bulletin, except as provided by paragraph (h) of this AD. Do all applicable corrective actions before further flight in accordance with the service bulletin, except as provided by paragraph (i) of this AD. Repeat the inspections at intervals not to exceed 4,500 flight cycles, until accomplishment of the repair/preventive change in accordance with the service bulletin, which terminates the repetitive inspections.

Exceptions to Service Bulletin Specifications

(h) Where Boeing Alert Service Bulletin 737-53A1188, Revision 2, dated May 9, 2007; and Boeing Alert Service Bulletin 737-53A1197, dated August 25, 2006, specify a compliance time after release of the service bulletin, this AD requires compliance within the specified time after the effective date of this AD.

(i) Where Boeing Alert Service Bulletin 737-53A1188, Revision 2, dated May 9, 2007; and Boeing Alert Service Bulletin 737-53A1197, dated August 25, 2006, specify to contact Boeing for appropriate action, including repair of damage outside the scope of the service bulletin, repair using a method approved in accordance with the procedures specified in paragraph (j) of this AD.

Alternative Methods of Compliance (AMOCs)

(j)(1) The Manager, Seattle Aircraft Certification Office (ACO), FAA, has the authority to approve AMOCs for this AD, if requested in accordance with 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 31, 2007.

Stephen P. Boyd,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.