E6-7011. Airworthiness Directives; Boeing Model 737-700 and 737-800 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 737-700 and 737-800 series airplanes. This proposed AD would require performing a one-time high frequency eddy current inspection for cracking of the backup intercostals located above the cutout for the forward airstair door; doing related investigative and corrective actions if any crack is found; and doing other specified corrective actions if no crack is found. This proposed AD results from a report of fatigue cracks discovered during a full-scale fatigue test conducted by the manufacturer. We are proposing this AD to detect and correct such cracking, which could result in more extensive fatigue cracking and lead to possible loss of cabin pressure.

DATES:

We must receive comments on this proposed AD by June 23, 2006.

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: Docket Management Facility, U.S. Department of Transportation, 400 Seventh Street, SW., Nassif Building, room PL-401, Washington, DC 20590.
• Fax: [phone].
• Hand Delivery: Room PL-401 on the plaza level of the Nassif Building, 400 Seventh Street, SW., 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 98055-4056; 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-2006-24698; Directorate Identifier 2006-NM-026-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 Management Facility office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management Facility office (telephone [phone]) is located on the plaza level of the Nassif 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

This proposed AD results from a report of fatigue cracks discovered parallel to a line of fasteners on the two backup intercostals of the upper sill web during a full-scale fatigue test conducted by Boeing. We also received a report that similar cracks and upper sill web cracks were discovered on a Model 737-300 series airplane. This condition, if not corrected, could result in more extensive fatigue cracking of the backup intercostals and upper sill web and lead to possible loss of cabin pressure.

Other Relevant Rulemaking

As previously mentioned, similar cracking was discovered on a Model 737-300 series airplane, and it has been determined that the unsafe condition also applies to certain Model 737-100, -200, -300, -400, and -500 series airplanes. The corrective action for those airplane models is similar to that proposed for Model 737-700 and 737-800 series airplanes; however, the corrective action will be different due to the higher number of flight cycles that have accumulated on these earlier airplane models. Because the corrective action will be different, Boeing intends to issue a separate service bulletin for Model 737-100, -200, -300, -400, and -500 series airplanes. We may consider further rulemaking when that service bulletin is issued and approved, rather than attempt to include all affected airplane models in this proposed AD.

Relevant Service Information

We have reviewed Boeing Special Attention Service Bulletin 737-53-1236, Revision 1, dated November 10, 2005. The service bulletin describes procedures for performing a one-time high frequency eddy current (HFEC) inspection for cracking of the backup intercostals of the airstair doorway upper sill; doing related investigative and corrective actions if any crack is found; and doing other specified corrective actions if no crack is found. Related investigative and corrective actions include performing an HFEC inspection for cracking at certain door stop fastener holes in the upper sill web and contacting Boeing for instructions on how to repair any crack discovered. Other specified corrective actions include installing replacement filler blocks and fasteners. Accomplishing the actions specified in the service information 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 under “Difference Between Proposed AD and Service Bulletin.”

Difference Between Proposed AD and Service Bulletin

The service bulletin specifies 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 146 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 54 airplanes of U.S. registry. The proposed HFEC inspection would take about 2 work hours per airplane, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the proposed AD for U.S. operators is $8,640, or $160 per airplane.

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-2006-24698; Directorate Identifier 2006-NM-026-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by June 23, 2006.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Boeing Model 737-700 and 737-800 series airplanes, certificated in any category; as identified in Boeing Special Attention Service Bulletin 737-53-1236, Revision 1, dated November 10, 2005.

Unsafe Condition

(d) This AD results from a report of fatigue cracks discovered during a full-scale fatigue test conducted by the manufacturer. We are issuing this AD to detect and correct such cracking, which could result in more extensive fatigue cracking and lead to possible loss of cabin pressure.

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.

Inspection of Backup Intercostals

(f) Before the accumulation of 24,000 total flight cycles, or within 4,500 flight cycles after the effective date of this AD, whichever comes later: Perform a high frequency eddy current (HFEC) inspection for cracking of the backup intercostals located above the cutout for the forward airstair door, and, before further flight, do related investigative actions and applicable corrective actions if any crack is found, and other specified corrective actions if no crack is found. Related investigative actions, applicable corrective actions and other specified corrective actions must be done in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-53-1236, Revision 1, dated November 10, 2005; except where the service bulletin specifies to contact Boeing for repair instructions, repair all cracks using a method approved in accordance with the procedures specified in paragraph (h) of this AD.

Actions Accomplished Using Original Issue of Service Bulletin

(g) Actions accomplished before the effective date of this AD in accordance with Boeing Service Bulletin 737-53-1236, dated July 11, 2002, are considered acceptable for compliance with the corresponding requirements of this AD.

Alternative Methods of Compliance (AMOCs)

(h)(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) Before using any AMOC approved in accordance with § 39.19 on any airplane to which the AMOC applies, notify the appropriate principal inspector in the FAA Flight Standards Certificate Holding District Office.

(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 April 28, 2006.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.