E9-10612. Airworthiness Directives; Boeing Model 737-300 and 737-400 Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 737-300 and 737-400 series airplanes. This proposed AD would require repetitive inspections to detect cracking of the aft fuselage skin, and related investigative/corrective actions if necessary. This proposed AD results from reports of cracks in the aft fuselage skin on both sides of the airplane. We are proposing this AD to detect and correct cracking in the aft fuselage skin along the longitudinal edges of the bonded skin doubler, which could result in reduced structural integrity of the airplane.

DATES:

We must receive comments on this proposed AD by June 22, 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, Attention: Data & Services Management, P.O. Box 3707, MC 2H-65, Seattle, Washington 98124-2207; telephone [phone], extension 1, 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 proposed 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:

Wayne Lockett, 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-2009-0429; Directorate Identifier 2007-NM-059-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 159 reports of cracks in the fuselage skin aft of the wing on 68 Model 737-300 series airplanes with between 16,400 and 48,000 total flight cycles. Of those cracks, 120 were found between body station (BS) 727D and BS 747 and between stringers 14 and 25, on both sides of the airplanes. One crack was found above stringer 25 right (R) at BS 913. Several of the cracks occurred in multiple adjacent bays. The remaining cracks were scattered between BS 727 and BS 1016.

A total of 29 cracks have been reported on 29 Model 737-400 series airplanes with between 22,500 and 44,600 total flight cycles. The cracks on these airplanes were found on both the left and right sides of the airplanes between BS 727 and BS 947 in the skin panels between stringers 20 and 25. The cracks ranged in length between 0.25 and 5.5 inches. One operator reported a crack on an airplane with 22,500 total flight cycles. The crack was in the skin panel assembly just above stringer 25R between BS 727+10 and BS 727, and between stringers 23R and 24R.

On the existing skin panel assembly, the doubler is bonded to the skin. At these skin panel locations on the airplane, the in-service loads cause a condition that allows cracks to occur along the longitudinal edges of the skin where it bonded to the doubler. Cracking, if not corrected, could result in reduced structural integrity of the airplane.

Relevant Service Information

We have reviewed Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006 (for Model 737-300 series airplanes); and Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007 (for Model 737-400 series airplanes). The service bulletins describe procedures for repetitive inspections to detect cracking of the aft fuselage skin; and related investigative and corrective actions, if necessary.

For Model 737-300 series airplanes, in areas without modification stiffeners installed previously, and for Model 737-400 series airplanes, the inspection technique to be used depends on the inspection zone. The inspection techniques include: External detailed and external subsurface eddy current; external general visual (in areas not covered by fairings); external detailed or subsurface eddy current (in areas covered by fairings); or external detailed, and either external subsurface eddy current or magneto optical imaging.

For Model 737-300 series airplanes, in areas with modification stiffeners installed previously, the inspections include: External general visual inspections of the surface of the skin panels for evidence of loose fasteners or skin cracking; and a one-time subsurface eddy current inspection for evidence of loose fasteners or skin cracks.

For all airplanes, related investigative and corrective actions include the following: Internal general visual and high frequency eddy current inspections for disbonding and cracking of the bonded doubler; repair or replacement of the skin panel; an internal inspection of the chem-milled step in the skin area covered by the doubler; replacement of the skin panel and splice plate between body stations (BS) 727 and 907 and between Stringers 20 and 25; and sending any positive inspection results to Boeing.

In addition, the service bulletins describe procedures for doing a time-limited repair, including a detailed inspection for cracking of the fuselage skin, and installing a repair doubler; repeating inspections of repaired areas; repairing any cracking; making the repairs permanent within a specified compliance time; and replacing any loose fasteners.

The service bulletins also specify that repeat inspections are terminated in areas where the skin panel replacement had been done, and in repaired areas that meet the requirements specified in Table 1 of paragraph 1.E. of the service bulletins.

The compliance times specified in the service bulletins are identified in the tables below.

Table—Compliance Times for Unmodified Areas

Action	Inspection zone 1	Inspection zone 2	Inspection zone 3
Zone and initial inspections	Before accumulating 22,000 total flight cycles, or within 4,500 flight cycles after the release date of the service bulletin, whichever is later.
Repetitive inspections	Option 1: Intervals not to exceed 3,700 flight cycles after the previous inspection; or	Intervals not to exceed 4,500 flight cycles after the previous inspection	Option 1: Intervals not to exceed 3,700 flight cycles after the previous inspection; or
	Option 2: Intervals not to exceed 2,100 flight cycles after the previous inspection		Option 2: Intervals not to exceed 2,100 flight cycles after the previous inspection.

Table—Compliance Times for Modified Areas

Action	Compliance times for all zones
Zone and initial inspections	Before accumulating 22,000 total flight cycles or within 4,500 flight cycles after the release date of the service bulletin, whichever is later.
Repetitive inspections	Intervals not to exceed 4,500 flight cycles after the previous inspection.
Terminating action	Not before 20,000 flight cycles following modification (Figure 5 of Boeing Service Bulletin 737-53-1168, Revision 3).

Table—Follow-on Actions and Compliance Times if the Time-Limited Repair Is Done

If you do the time-limited repair, you must—	At this compliance time—
Do a detailed inspection of the fastener	At intervals not to exceed 3,000 flight cycles following the repair.
Replace a blind fastener with a solid fastener	Before the repair has reached 10,000 total flight cycles.
Do an internal inspection of the tear strap for disbonding and cracks	Within 4,500 flight cycles following the repair.

FAA's Determination and Requirements of This Proposed AD

We are proposing this AD because we evaluated all relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of the(se) same type design(s). This proposed AD would require accomplishing the actions specified in the service information described previously, except as discussed under “Differences Between the Proposed AD and Service Information.”

Differences Between the Proposed AD and Service Information

The service bulletins specify 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.

Although the service bulletins referenced in this proposed AD specify to submit information to the manufacturer, this proposed AD does not include such a requirement.

Costs of Compliance

We estimate that this proposed AD would affect 516 airplanes of U.S. registry. The following table provides the estimated costs for U.S. operators to comply with this proposed AD. The average labor rate is $80 per work hour.

Estimated Costs

Action	Work hours	Parts	Cost per product	Number of U.S.- registered airplanes	Fleet cost
Inspection to determine inspection zones	1	$0	$80	516	$41,280.
Repetitive inspections—Option 1	64	0	$5,120, per inspection cycle	516	Up to $2,641,920.
Repetitive inspections—Option 2	62	0	$4,960, per inspection cycle	516	Up to $2,559,360.
Internal inspection	5, per inspection zone (3 zones)	0	$1,200	516	$619,200.

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 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 this 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.

You can find our regulatory evaluation and the estimated costs of compliance in the AD Docket.

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 FAA amends § 39.13 by adding the following new AD:

Boeing: Docket No. FAA-2009-0429; Directorate Identifier 2007-NM-059-AD.

Comments Due Date

(a) We must receive comments by June 22, 2009.

Affected ADs

(b) None.

Applicability

(c) This AD applies to the airplanes identified in paragraphs (c)(1) and (c)(2) of this AD, certified in any category.

(1) Boeing Model 737-300 series airplanes as identified in Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006.

(2) Boeing Model 737-400 series airplanes as identified in Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007.

Subject

(d) Air Transport Association (ATA) of America Code 53: Fuselage.

Unsafe Condition

(e) This AD results from reports of cracks in the aft fuselage skin on both sides of the airplane. We are issuing this AD to detect and correct cracking in the aft fuselage skin along the longitudinal edges of the bonded skin doubler, which could result in reduced structural integrity of the airplane.

Compliance

(f) Comply with this AD within the compliance times specified, unless already done.

Inspections, Related Investigative and Corrective Actions

(g) At the applicable times specified in Tables 1 and 2 of paragraph 1.E. “Compliance,” of Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006 (for Model 737-300 series airplanes); or Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007 (for Model 737-400 series airplanes); except as provided by paragraph (k) of this AD: Do the applicable inspections and related investigative actions to detect cracks in the aft fuselage skin panels, by accomplishing all of the applicable actions specified in the Accomplishment Instructions of Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006; or Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007; as applicable, including Note (f) of Table 1 of paragraph 1.E. And, do the applicable corrective actions specified in the Accomplishment Instructions of Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006; or Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007; as applicable; except as provided by paragraphs (h), (i), and (l) of this AD. Repeat the applicable inspections and related investigative actions thereafter at the applicable intervals specified in Tables 1 and 2 of paragraph 1.E. of Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006; or Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007; as applicable.

(h) If any crack is found during any inspection or corrective action required by this AD, before further flight, repair in accordance with the Accomplishment Instructions of Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006 (for Model 737-300 series airplanes); or Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007 (for Model 737-400 series airplanes); except, where Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006; or Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007; as applicable; specifies to contact Boeing, before further flight, repair according to a method approved in accordance with the procedures specified in paragraph (m) of this AD.

(i) If any cracking of a repaired area is found during any inspection required by this AD, and Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006 (for Model 737-300 series airplanes); or Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007 (for Model 737-400 series airplanes); specifies contacting Boeing for appropriate action: Before further flight, repair the cracking using a method approved in accordance with the procedures specified in paragraph (m) of this AD.

Optional Terminating Action

(j) Doing the skin panel replacement in accordance with Part 3 of the Accomplishment Instructions of Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006 (for Model 737-300 series airplanes); or Part III of the Accomplishment Instructions of Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007 (for Model 737-400 series airplanes); terminates the inspection requirements of paragraph (g) of this AD for that skin panel only.

Exception to Service Bulletin

(k) Where Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006 (for Model 737-300 series airplanes); or Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007 (for Model 737-400 series airplanes); specifies compliance times after the release date of those service bulletins, this AD requires that the specified actions be done within the specified compliance times after the effective date of this AD.

No Reporting Required

(l) Although Boeing Service Bulletin 737-53-1168, Revision 3, dated November 28, 2006 (for Model 737-300 series airplanes); and Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007 (for Model 737-400 series airplanes); specify to submit information to the manufacturer, this AD does not include such a requirement.

Alternative Methods of Compliance (AMOCs)

(m)(1) The Manager, Seattle Aircraft Certification Office (ACO), FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. Send information to ATTN: Wayne Lockett, Aerospace Engineer, Airframe Branch, ANM-120S, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone [phone]; fax [phone]. Or, e-mail information to [e-mail].

(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 principal maintenance inspector (PMI) or principal avionics inspector (PAI), as appropriate, or lacking a principal inspector, your local Flight Standards District Office. The AMOC approval letter must specifically reference this AD.

(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 May 1, 2009.

Stephen P. Boyd,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.