E8-28819. 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 detailed and high frequency eddy current inspections to detect cracks of the backup intercostals and the upper sill of the forward airstair doorway, and applicable corrective actions. This proposed AD would also provide for an optional terminating action, which would eliminate the need for repetitive inspections. This proposed AD results from a report indicating that cracks were found in the backup intercostals and upper sill web of the forward airstair doorway. We are proposing this AD to detect and correct fatigue cracking of the backup intercostals and upper sill web of the forward airstair doorway, which could result in a rapid loss of cabin pressure.

DATES:

We must receive comments on this proposed AD by January 20, 2009.

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; telephone [phone]; fax [phone]; e-mail [e-mail]; Internet https://www.myboeingfleet.com. You may review copies of the referenced service information at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington. For information on the availability of this material at the FAA, call 425-227-1221 or 425-227-1152.

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 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:

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 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-2008-1275; Directorate Identifier 2007-NM-167-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 have received a report indicating that cracks were found in the backup intercostals and upper sill web of the forward airstair doorway on a Boeing Model 737-200 series airplane. The cracks were found in the upper sill web at the stop fitting at station (STA) 312 and in the two backup intercostals of the stop support structure at STA 322.7 and STA 333.3. Investigation revealed the cracks are due to fatigue caused by cyclic loads acting on the upper sill web, which is stabilized by the backup intercostals. Fatigue cracking of the backup intercostals and upper sill web of the forward airstair doorway, if not detected and corrected, could result in a rapid loss of cabin pressure.

The configuration of the subject area on certain Boeing Model 737-100, -200C, -300, -400, and -500 series airplanes is almost identical to that on the affected Boeing Model 737-200 series airplanes. Therefore, those Boeing Model 737-100, -200C, -300, -400, and -500 series airplanes are subject to the unsafe condition revealed on the Boeing Model 737-200 series airplanes.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 737-53A1269, dated May 17, 2007. The service bulletin describes procedures for repetitive detailed and high frequency eddy current inspections to detect fatigue cracking of the backup intercostals and the upper sill web of the forward airstair doorway, and applicable corrective actions. The service bulletin also describes procedures for an optional terminating action, which would eliminate the need for the repetitive inspections.

The corrective and optional terminating actions include doing a repair/preventive modification to install new backup intercostals with radius fillers, installing the preventive modification filler and doubler plate, and repairing any cracked upper sill web.

The service information also specifies the following compliance times:

• For the initial inspections: The threshold is prior to 45,000 or 49,500 total flight cycles depending on the flight cycles on the airplane. The grace period is 1,000 or 4,500 flight cycles depending on the flight cycles on the airplane.
• For the applicable repetitive inspections: The compliance time is at intervals of 4,500 flight cycles.
• For the applicable corrective actions: The compliance time is before further flight.

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 certain actions specified in the service information described previously. The proposed AD also provides for an optional terminating action, as specified in the service bulletin, for the repetitive inspection requirements.

Costs of Compliance

There are about 1,712 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 509 airplanes of U.S. registry. The proposed inspections 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 would be $81,440, or $160 per airplane, per inspection cycle.

The optional terminating action, if done, would take about 9 work hours, at an average labor rate of $80 per work hour. Required parts would cost between $533 and $566 per airplane, depending on the airplane configuration. Based on these figures, the estimated cost of the optional terminating action would range between $1,253 and $1,286 per airplane, 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 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
• Incorporation by reference
• 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-2008-1275; Directorate Identifier 2007-NM-167-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by January 20, 2009.

Affected ADs

(b) None

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 Alert Service Bulletin 737-53A1269, dated May 17, 2007.

Unsafe Condition

(d) This AD results from a report indicating that cracks were found in the backup intercostals and upper sill web of the forward airstair doorway. We are issuing this AD to detect and correct fatigue cracking of the backup intercostals and upper sill web of the forward airstair doorway, which could result in a rapid 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.

Inspections

(f) At the applicable compliance times and repeat intervals listed in the tables of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1269, dated May 17, 2007 (hereafter “the service bulletin”), except as provided by paragraphs (f)(1), (f)(2), and (f)(3) of this AD: Do repetitive detailed and high frequency eddy current inspections to detect cracks of the backup intercostals and the upper sill of the forward airstair doorway, and applicable corrective actions by accomplishing all the applicable actions specified in the Accomplishment Instructions of the service bulletin. Do the applicable corrective actions before further flight.

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

(2) Where the columns identified as “Airplane Flight Cycles” in the tables of the service bulletin specify less than 45,000 total flight cycles for certain actions, this AD affects airplanes having less than or equal to 45,000 total flight cycles.

(3) Where the columns identified as “Repeat Interval” in the tables of the service bulletin specify an interval of 4,500 flight cycles for all conditions, this AD requires repetitive inspections only if no crack is found during any inspection required by paragraph (f) of this AD.

Optional Terminating Action

(g) Accomplishing the backup intercostal repair/preventative modification and/or the upper door sill web repair, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1269, dated May 17, 2007, ends all the corresponding repetitive inspection requirements of paragraph (f) of this AD.

Alternative Methods of Compliance (AMOCs)

(h)(1) The Manager, Seattle Aircraft Certification Office (ACO), FAA, ATTN: Howard Hall, 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, FAA, 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 November 26, 2008.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.