E7-16657. Airworthiness Directives; Boeing Model 737-600, -700, -700C, -800, and -900 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 737-600, -700, -700C, -800, and -900 series airplanes. This proposed AD would require repetitive inspections of either the aft side or forward side of the aft pressure bulkhead for oil can conditions or bulges, a one-time inspection of the aft pressure bulkhead to identify any previously installed web repair, and corrective actions if necessary. This proposed AD results from web oil can conditions found on the aft pressure bulkhead of several airplanes. We are proposing this AD to detect and correct oil can conditions, bulges, or previous repairs in the aft pressure bulkhead, which could lead to web cracks and consequently result in rapid decompression of the airplane.

DATES:

We must receive comments on this proposed AD by October 9, 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-2007-29031; Directorate Identifier 2007-NM-130-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 a report indicating that “oil cans” or “bulges” have been found on the aft pressure bulkhead web of several Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes. (An oil can is defined as an area on the pressure dome web that has visibly deviated forward from the initial contour of the pressured dome web. A bulge is defined as an area on the pressure dome web that has visibly deviated aft from the initial contour of the pressure dome web.) Oil can conditions or bulges in the aft pressure bulkhead, if not corrected, could lead to web cracks and consequently result in rapid decompression of the airplane.

In addition, some operators may have previously repaired an oil can condition in accordance with the Boeing 737-600/700/700C/800/900 Structural Repair Manuals (SRMs). The latest revision of the SRM currently requires accomplishing an initial nondestructive testing (NDT) inspection of the repair and incorporating repetitive supplemental inspections of the repair into the airplane's maintenance program. Repair procedures in earlier revisions of the SRMs did not specify doing an initial NDT inspection and/or repetitive supplemental inspections. If the initial NDT inspection and repetitive supplemental inspections of the repair are not accomplished, web cracks could also develop and consequently result in loss of cabin pressurization.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 737-53A1253, dated May 18, 2007. The service bulletin describes procedures for doing repetitive general visual inspections of either the aft side or forward side of the aft pressure bulkhead for oil can conditions or bulges, a one-time general visual inspection of the aft pressure bulkhead to identify any previously installed web repair, and corrective actions as applicable. The corrective actions include:

• If the oil can condition is within a certain limit, (1) doing repetitive inspections of aft pressure bulkhead for web cracks until an oil can condition is repaired, or (2) before further flight, doing one-time NDT inspections of aft pressure bulkhead for web cracks and repairing the oil can condition.
• If the oil can condition is beyond a certain limit, doing a one-time NDT inspection of the affected web bay at the fastener locations where the web intersects the surrounding structure for cracks and repairing the oil can condition.
• If existing bulkhead repairs or bulging of tear straps prevent accomplishing low and high frequency eddy current inspections, contacting Boeing for instructions.
• Repairing any cracks or bulges found during any inspection and contacting Boeing for repair instructions if necessary.
• If a previously installed oil can repair is found, doing one-time NDT inspections of the web at the surrounding structure interfaces for cracks.
• If follow-on supplemental inspections of a previously installed repair are not being accomplished, determining the FAA-approved, follow-on inspection procedures, thresholds, and repetitive intervals and incorporating them into the airplane maintenance program.

Table 1 of paragraph 1.E. of the service bulletin recommends the following compliance times for the general visual inspections for oil can conditions or bulges in the aft pressure bulkhead: (1) The initial inspection at or before 15,000 total flight cycles or within 1,200 flight cycles from the release date of the bulletin, (2) the first repetitive inspection thereafter at or before 10,000 flight cycles, and (3) the subsequent repetitive general visual inspections thereafter at or before 6,000 flight cycles. Table 1 also recommends repairing an oil can condition at or before 12,000 flight cycles, or before further flight, depending upon the extent of the oil can condition. Table 1 also recommends repairing any crack or bulge before further flight.

Table 2 of paragraph 1.E. of the service bulletin specifies a compliance time of 15,000 total flight cycles or within 1,200 flight cycles after the date on the service bulletin, for doing the one-time general visual inspection to identify repairs to the gore web (i.e., the tapered web segments). If any repair is found that does not have follow-on supplemental inspections, Table 2 specifies to determine the FAA-approved, follow-on inspection procedures, thresholds, and repetitive intervals and to incorporate them into the airplane maintenance program within 12 months after accomplishing the inspection given in Section 53-80-08-2R of the Boeing 737-600/700/700C/800/900 SRMs.

For Model 737-700 and -800 series airplanes on which Boeing Business Jet (BBJ) Lower Cabin Altitude Modification has been incorporated in accordance with Supplemental Type Certificate (STC) ST01697SE: Paragraph 1.E. of the service bulletin recommends that all initial compliance times (thresholds) specified in flight cycles be reduced to one-half of those specified in the service bulletin, and that all repeat interval compliance times specified in flight cycles be reduced to one-quarter of those specified in the service bulletin.

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 “Differences Between the Proposed AD and Service Bulletin.”

Differences Between the 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.

The service bulletin specifies to contact Boeing for further instructions in developing an FAA-approved supplemental inspection program if an aft pressure bulkhead is found that does not have supplemental inspections specified in either the Boeing 737-600/700/700C/800/900 SRMs or the service bulletin. This proposed AD would instead require contacting the Manager, Seattle Aircraft Certification Office, or an Authorized Representative for the Boeing Commercial Airplanes Delegation Option Authorization Organization.

If any repair is found that does not have follow-on supplemental inspections, Table 2 of paragraph 1.E. of the service bulletin specifies to determine the FAA-approved follow-on inspections procedures, thresholds, and repetitive intervals and to incorporate them into the airplane maintenance program within 12 months after accomplishing the inspection in Section 53-80-08-2R of the Boeing 737-600/700/700C/800/900 SRMs. This proposed AD, however, would require that those corrective actions, if applicable, be done within 12 months after accomplishing the one-time general visual inspection of the aft pressure bulkhead for any previously installed web repair.

Tables 1 and 2 of paragraph 1.E. of the service bulletin specify a compliance time of 15,000 total flight cycles or within 1,200 flight cycles from the release date or after the date on the service bulletin, for the general visual inspections. This proposed AD would require accomplishing the applicable inspection at the later of those compliance times. This proposed AD would also require starting the compliance time from the effective date of this AD, not from the service bulletin date.

Although the service bulletin specifies to submit certain information to the manufacturer, this proposed AD does not include that requirement. We do not need this information from operators.

Costs of Compliance

There are about 1,755 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 600 airplanes of U.S. registry. The proposed inspection would take about 6 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 $288,000, or $480 per airplane, per inspection cycle.

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-2007-29031; Directorate Identifier 2007-NM-130-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by October 9, 2007.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes, certificated in any category; as identified in Boeing Alert Service Bulletin 737-53A1253, dated May 18, 2007.

Unsafe Condition

(d) This AD results from web oil can conditions found on the aft pressure bulkhead of several airplanes. We are issuing this AD to detect and correct oil can conditions, bulges, or previous repairs in the aft pressure bulkhead, which could lead to web cracks and consequently 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) At the applicable times specified in paragraph 1.E. of Boeing Alert Service Bulletin 737-53A1253, dated May 18, 2007, except as provided by paragraph (g) of this AD: Do repetitive general visual inspections of either the aft side or forward side of the aft pressure bulkhead for oil can conditions or bulges and a one-time general visual inspection of the aft pressure bulkhead to identify any previously installed web repair, and do all applicable corrective actions, by accomplishing all of the applicable actions specified in the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1253, dated May 18, 2007, except as provided by paragraphs (h) and (i) of this AD.

Exceptions to Compliance Times

(g) Where Tables 1 and 2 of paragraph 1.E. of Boeing Alert Service Bulletin 737-53A1253, dated May 18, 2007, specify a compliance time of “at or before 15,000 total flight cycles or within 1,200 flight cycles” for the general visual inspections, this AD would require accomplishing the applicable inspection at the later of those compliance times. Where Tables 1 and 2 of paragraph 1.E. of the service bulletin specify counting the compliance time from the “release date of this service bulletin” or “after the date on this service bulletin,” this proposed requires starting the compliance time from the effective date of this AD. Where Table 2 of paragraph 1.E. of the service bulletin specifies to determine the FAA-approved, follow-on inspection procedures, thresholds, and repeat intervals and to incorporate them into the airplane maintenance program within 12 months after accomplishing the inspection given in Section 53-80-08-2R of the Boeing 737-600/700/700C/800/900 Structural Repair Manuals (SRMs), this AD requires that those corrective actions, if applicable, be done within 12 months after accomplishing the one-time general visual inspection of the aft pressure bulkhead for any previously installed web repair as required by paragraph (f) of this AD.

Exceptions to Corrective Actions

(h) If any crack or bulge is found during any inspection required by paragraph (f) of this AD and Boeing Alert Service Bulletin 737-53A1253, dated May 18, 2007, specifies to contact Boeing for repair instructions, before further flight, repair according to a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, or according to data meeting the certification basis of the airplane approved by an Authorized Representative for the Boeing 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. If a previously installed aft pressure bulkhead web repair is found during any inspection required by paragraph (f) of this AD, and the FAA-approved supplemental inspection program cannot be determined from either the Boeing 737-600/700/700C/800/900 SRMs or the service bulletin, and the service bulletin specifies to contact Boeing for further instructions, within 12 months after accomplishing the inspection, contact the Manager, SACO, or an Authorized Representative for the Boeing Commercial Airplanes Delegation Option Authorization Organization to develop a supplemental inspection program.

No Reporting Requirement

(i) Although Boeing Alert Service Bulletin 737-53A1253, dated May 18, 2007, specifies to submit certain information to the manufacturer, this AD does not require that action.

Alternative Methods of Compliance (AMOCs)

(j)(1) The Manager, Seattle ACO, 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 14 CFR 25.571, Amendment 45, and the approval must specifically refer to this AD.

Issued in Renton, Washington, on August 14, 2007.

Stephen P. Boyd,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.