E7-20048. 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 all Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. This proposed AD would require repetitive inspections for cracking in and around the upper and lower hinge cutouts of the forward entry and forward galley service doorways, and corrective actions if necessary. This proposed AD results from multiple reports of cracks found in the skin, bearstrap, and/or frame outer chord in the hinge cutout areas of the forward entry and forward galley service doorways. We are proposing this AD to detect and correct such cracking, which could result in rapid decompression of the airplane.

DATES:

We must receive comments on this proposed AD by November 26, 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-2007-0024; Directorate Identifier 2007-NM-086-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 multiple reports of cracks found in the skin, bearstrap, and/or frame outer chord in the hinge cutout areas of the forward entry and forward galley service doorways. Cracks in the forward entry door bearstrap were reported on an airplane with as few as 24,538 total flight cycles. Cracks in the forward galley service door bearstrap were reported on an airplane with as few as 44,938 total flight cycles. One operator reported a severed bearstrap, a severed station (STA) 291.5 frame, and a 14.5-inch crack in the skin at the lower hinge cutout of the forward galley service doorway. The airplane had accumulated 61,297 total flight cycles. Such cracking, if not corrected, could result in rapid decompression of the airplane.

The fatigue cracks are caused by cyclic cabin pressure loads and are not due to manufacturing defects in the bearstrap. The unsafe condition is unrelated to any previous investigation related to suspected unapproved parts.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 737-53A1200, dated April 13, 2006. The service bulletin describes procedures for repetitive inspections for cracking in and around the upper and lower hinge cutouts of the forward entry and forward galley service doorways. The service bulletin describes the following inspections:

• External detailed inspection of the skin;
• High frequency eddy current (HFEC) hole probe inspection of the skin, bonded doubler, bearstrap, and frame chord at specified fastener locations;
• HFEC hole probe inspection of the skin, bonded doubler, and bearstrap at specified fastener locations aft of the frame chord;
• HFEC inspection of the skin hinge cutout trim;
• Low frequency eddy current (LFEC) hole probe inspection of the skin, bonded doubler, and bearstrap at specific fastener locations aft of the frame chord;
• LFEC hole probe inspection of the skin, bonded doubler, bearstrap, and frame chord at specific fastener locations.

The service bulletin provides two options for the inspections, as follows:

Compliance Times

Option	Inspections	Threshold, in total flight cycles	Grace period, in flight cycles	Repetitive interval, in flight cycles
A 1	External detailed inspection; HFEC inspection of the skin hinge cutout trim; and HFEC rotary probe inspection of the entire zone	Entry door: 20,000 Service door: 40,000.	3,000	18,000
B	External detailed inspection; HFEC inspection of the skin hinge cutout trim; and LFEC inspection of the entire zone	Entry door: 20,000 Service door: 40,000.	3,000	3,000
	HFEC rotary probe inspection of the aft zone (required only for Group 1, Configuration 1, and only for the entry door)	Entry door: 20,000 Service door: 40,000.	6,000	18,000
1 Option A is mandatory for the forward entry door, upper and lower hinge cutouts, on Model 737-200C airplanes.

The service bulletin specifies contacting Boeing for crack repair instructions.

The service bulletin also states that the service bulletin might in the future be revised to include a preventive modification that will eliminate the need for the repetitive inspections. The service bulletin specifies contacting Boeing for information about this modification.

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 the Proposed AD and the Service Bulletin

The service bulletin specifies contacting the manufacturer for instructions for crack repair and for an optional modification that would terminate the repetitive inspections. But this proposed AD would require doing the repair and optional modification 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 2,437 airplanes of the affected design in the worldwide fleet. The following table provides the estimated costs for U.S. operators to comply with this proposed AD, per inspection cycle.

Estimated Costs

Work hours	Average hourly labor rate	Cost per airplane	Number of U.S.-registered airplanes	Fleet cost
13 to 14	$80	$1,040 to $1,120	1,055	$1,097,200 to $1,181,600

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-2007-0024; Directorate Identifier 2007-NM-086-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by November 26, 2007.

Affected ADs

(b) None.

Applicability

(c) This AD applies to all Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes, certificated in any category.

Unsafe Condition

(d) This AD results from multiple reports of cracks found in the skin, bearstrap, and/or frame outer chord in the hinge cutout areas of the forward entry and forward galley service doorways. We are issuing this AD to detect and correct such cracking, which could result in rapid 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

(f) Except as provided by paragraph (g) of this AD, at the applicable times specified in paragraph 1.E. of Boeing Alert Service Bulletin 737-53A1200, dated April 13, 2006, do external detailed, low frequency eddy current, high frequency eddy current, and high frequency eddy current rotary probe inspections, as applicable, for cracks in and around the upper and lower hinge cutouts of the forward entry and forward galley service doorways, in accordance with the Accomplishment Instructions of the service bulletin, except as provided by paragraph (h) of this AD. Do not exceed the applicable repetitive interval for the previous inspection, as specified in the service bulletin as Option A or Option B. Repair any crack before further flight using a method approved in accordance with the procedures specified in paragraph (i) of this AD.

Exceptions to Service Bulletin Specifications

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

(h) Although the service bulletin specifies contacting Boeing for information about installing an optional preventive modification that would terminate the repetitive inspections specified in this AD, this AD requires that any terminating action be done by using a method approved in accordance with the procedures specified in paragraph (i) of this AD.

Alternative Methods of Compliance (AMOCs)

(i)(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 October 1, 2007.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.