E6-5723. 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 cracks in the vertical beam webs of the body station (BS) 178 bulkhead, and corrective actions if necessary. This proposed AD also would require a terminating modification for the repetitive inspections. This proposed AD results from reports of numerous cracks in the vertical beam webs. We are proposing this AD to prevent fatigue cracks in certain vertical beam webs, which could result in loss of structural integrity of the BS 178 bulkhead, and consequently could impair the operation of the control cables for the elevators, speed brakes, and landing gear, or could cause the loss of cabin pressure.

DATES:

We must receive comments on this proposed AD by June 2, 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-2006-24496; Directorate Identifier 2005-NM-141-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

We have received several reports of numerous cracks in the vertical beam webs at buttock lines (BL) 5.7 and 17.0 of the body station (BS) 178 bulkhead on Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes, line numbers 1 through 3132 inclusive. Five cracks nearly severed the upper web of the BL 17.0 vertical beam. One crack severed the lower web of the BL 17.0 vertical beam. The cracks initiate from holes in the web of the vertical beams and at fastener locations common to the forward and aft chords of the vertical beams. These airplanes have accumulated between 15,556 and 64,881 total flight cycles. The cracks occur as a result of structural fatigue due to cabin pressure loads. Fatigue cracks in the vertical beam webs at BL 5.7 and 17.0 of BS 178 bulkhead, if not detected and corrected, could result in loss of structural integrity of the bulkhead, which could impair the operation of the control cables for the elevators, speed brakes, and landing gear, or could cause the loss of cabin pressure.

Other Relevant Rulemaking

We have previously issued AD 2000-05-29, amendment 39-11639 (65 FR 14834, March 20, 2000), applicable to Boeing Model 737-100, -200, -300, -400, and -500 series airplanes, line numbers 1 through 2,737 inclusive. That AD requires repetitive inspections to detect fatigue cracking of the web, vertical chords, and side chords of the forward pressure bulkhead, and repair if necessary. That AD also provides for certain optional preventative modifications (reference Boeing Alert Service Bulletin 737-53A1173, Revision 3, dated May 6, 1999), which, if done, ends the repetitive inspection requirements for the affected areas.

In addition, we have previously issued AD 2001-02-01, amendment 39-12085 (66 FR 7576, January 24, 2001), applicable to Boeing Model 737-300, -400, and -500 series airplanes, line numbers 2,738 through 3,071 inclusive. That AD requires repetitive inspections to detect fatigue cracking in the vertical chords and side chords of the forward pressure bulkhead, and repair if necessary. That AD also requires certain preventative modifications (reference Boeing Alert Service Bulletin 737-53A1208, dated May 6, 1999), which ends the repetitive inspection requirements for the affected areas.

For certain airplanes, accomplishing the preventative modification in this proposed AD may affect accomplishing the preventative modifications specified as optional in AD 2000-05-29 and required by AD 2001-02-01. See “Effect of Accomplishing Concurrent Requirements” section for further information.

Relevant Service Information

We have reviewed Boeing Service Bulletin 737-53A1225, Revision 1, dated April 14, 2005. The service bulletin describes procedures for repetitive high frequency eddy current (HFEC) and detailed inspections to detect cracks in the BS 178 vertical beam webs, and corrective actions if necessary. The corrective actions include repairing or replacing any cracked vertical beam web and associated parts with a new vertical beam web and associated parts. The service bulletin also describes procedures for a preventative modification (i.e., repairing or replacing the vertical beams at BL 5.7 and 17.0 of the BS 178 bulkhead), which ends the repetitive inspections. For certain airplanes, Boeing Service Bulletin 737-53A1225 recommends accomplishing concurrently the terminating preventative modifications specified in Boeing Alert Service Bulletin 737-53A1173 or 737-53A1208, as applicable, due to common access and structure.

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 the Proposed AD and Service Information.”

Difference Between Proposed AD and Service Information

Boeing Service Bulletin 737-53A1225 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.

Effect of Accomplishing Concurrent Requirements

Operators who have not done the preventative modifications specified in AD 2000-05-29 (reference Boeing Alert Service Bulletin 737-53A1173, Revision 3, dated May 6, 1999) or required by AD 2001-02-01 (reference Boeing Alert Service Bulletin 737-53A1208, dated May 6, 1999), as applicable, as of the effective date of this AD, must do those preventative modifications concurrently with the preventative modification of this proposed AD in accordance with Boeing Service Bulletin 737-53A1225, Revision 1. We realize that the concurrent requirements of this proposed AD will force some operators to do the preventative modifications required by AD 2001-02-01 early and to do the optional preventative modification specified in AD 2000-05-29. However, accomplishing the applicable preventative modifications together is necessary to avoid repeated disassembly and re-assembly of common parts, which increases the likelihood of additional assembly errors.

Costs of Compliance

There are about 3,132 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.

Estimated Costs

Action	Work hours	Average labor rate per hour	Parts	Cost per airplane	Number of U.S.-registered airplanes	Fleet cost
Inspection, per inspection cycle	4	$80	None	$320, per inspection cycle	1,172	$375,040, per inspection cycle.
Preventative Modification	240	80	Between $960 and $13,620 depending on kit purchased	Between $20,160 and $32,820 depending on configuration	1,172 (720 airplanes have had the preventative modification incorporated)	Between $14,515,200 and $23,630,400.

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-2006-24496; Directorate Identifier 2005-NM-141-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by June 2, 2006.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Boeing Model 737-100, -200, -200C, -300, -400, -500 series airplanes, certificated in any category; as identified in Boeing Service Bulletin 737-53A1225, Revision 1, dated April 14, 2005.

Unsafe Condition

(d) This AD results from reports of numerous cracks in the vertical beam webs. We are issuing this AD to prevent fatigue cracks in certain vertical beam webs, which could result in loss of structural integrity of the body station (BS) 178 bulkhead, and consequently could impair the operation of the control cables for the elevators, speed brakes, and landing gear, or could cause the 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.

Repetitive Inspections

(f) At the applicable times specified in Table 1 of this AD, do a high frequency eddy current (HFEC) inspection and detailed inspection to detect cracks in the BS 178 vertical beam webs, in accordance with the Accomplishment Instructions of Boeing Service Bulletin 737-53A1225, Revision 1, dated April 14, 2005.

Table 1.—Compliance Times

For airplanes on which—	Inspect—	And repeat the HFEC and detailed inspections thereafter at—
(1) An HFEC or a detailed inspection specified in Boeing Service Bulletin 737-53A1225, dated October 19, 2000, has not been done as of the effective date of this AD	Before the accumulation of 15,000 total flight cycles, or within 4,500 flight cycles after the effective date of this AD, whichever occurs later	Intervals not to exceed 6,000 flight cycles.
(2) An HFEC or detailed inspection specified in Boeing Service Bulletin 737-53A1225, dated October 19, 2000, has been done before the effective date of this AD	Within 6,000 flight cycles since the last HFEC inspection, or within 1,200 flight cycles since the last detailed inspection, whichever occurs later	Intervals not to exceed 6,000 flight cycles.

Corrective Actions

(g) If any crack is detected during any inspection required by paragraph (f) of this AD, before further flight, repair or replace the vertical beam web and associated parts with a new vertical beam web, in accordance with the Accomplishment Instructions of Boeing Service Bulletin 737-53A1225, Revision 1, dated April 14, 2005, except as provided by paragraph (h) of this AD.

(h) If any damage is beyond the scope of the service bulletin or structural repair manual, before further flight, repair the damaged vertical beam web in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA; or using a method approved in accordance with paragraph (l) of this AD.

Terminating Preventative Modification

(i) Before the accumulation of 50,000 total flight cycles, or within 25,000 flight cycles after the effective date of this AD, whichever occurs later, repair or replace the vertical beams at buttock lines (BL) 5.7 and 17.0 of the BS 178 bulkhead, in accordance with the Accomplishment Instructions of Boeing Service Bulletin 737-53A1225, Revision 1, dated April 14, 2005. Accomplishing the repair or replacement ends the repetitive inspections required by paragraph (f) of this AD.

(j) Actions done before the effective date of this AD in accordance with Boeing BOECOM M-7200-01-00546, dated March 1, 2001, are acceptable for compliance with the requirements of paragraph (i) of this AD.

Concurrent Requirements

(k) For Group 1 airplanes identified in Boeing Service Bulletin 737-53A1225, Revision 1, dated April 14, 2005: Concurrently with the requirements of paragraph (i) of this AD, unless already done before the effective date of this AD, do the preventative modifications of the center web, vertical chords, and side chord areas, including the side chord areas at water line 207, of the forward pressure bulkhead, specified in paragraph (c) of AD 2000-05-29, amendment 39-11639 (reference Boeing Alert Service Bulletin 737-53A1173, Revision 3, dated May 6, 1999).

(l) For Group 2 airplanes identified in Boeing Service Bulletin 737-53A1225, Revision 1, dated April 14, 2005: Concurrently with the requirements of paragraph (i) of this AD, but no later than the time specified in AD 2001-02-01, amendment 39-12085, do the preventative modifications of the vertical and side chord areas of the forward pressure bulkhead required by paragraph (c) of AD 2001-02-01 (reference Boeing Alert Service Bulletin 737-53A1208, dated May 6, 1999).

Alternative Methods of Compliance (AMOCs)

(m)(1) The Manager, Seattle 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 4, 2006.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.