E8-12712. Airworthiness Directives; Boeing Model 747 Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

We propose to adopt a new airworthiness directive (AD) for all Boeing Model 747 airplanes. This proposed AD would require inspecting for cracks in the left- and right-side Stringer 11 longeron adjacent to the horizontal stabilizer pivot bulkhead, and related investigative and corrective actions if necessary. This proposed AD results from a report of a crack found in the right-side Stringer 11 longeron horizontal flange, adjacent to the horizontal stabilizer pivot bulkhead, during a routine maintenance inspection. We are proposing this AD to detect and correct fatigue cracking of the longeron, which can propagate and cause damage to the adjacent horizontal stabilizer pivot bulkhead. This damage could result in loss of structural integrity and consequent inability of the bulkhead to carry flight loads, which could adversely affect controllability of the airplane.

DATES:

We must receive comments on this proposed AD by July 21, 2008.

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.

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:

Ivan Li, 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-2008-0612; Directorate Identifier 2008-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 received a report of a crack found in the right-side Stringer 11 longeron horizontal flange, adjacent to the horizontal stabilizer pivot bulkhead, during a routine maintenance inspection. The airplane had accumulated 28,311 total flight hours and 22,070 total flight cycles. The crack was visible in the exposed inboard edge of the longeron horizontal flange between the upper and lower Station 2598 horizontal stabilizer pivot bulkhead splice fittings. After removal of the fittings it was revealed that the crack had propagated and completely severed the longeron. Boeing analysis indicates that the severed longeron was a result of fatigue that had originated from a fastener hole in the longeron horizontal flange. Fatigue cracking of the longeron can propagate and cause damage to the adjacent horizontal stabilizer pivot bulkhead. This condition, if not corrected, could result in loss of structural integrity and consequent inability of the bulkhead to carry flight loads, which could adversely affect controllability of the airplane.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 747-53A2703, dated February 14, 2008. The service bulletin describes procedures for a surface high frequency eddy current (HFEC) inspection for cracks in the left- and right-side Stringer 11 longeron exposed surfaces and edges between Stations 2598 and 2607 adjacent to the horizontal stabilizer pivot bulkhead, and related investigative and corrective actions if necessary. The procedures for the related investigative and corrective actions are as follows:

• If any crack is found during the surface HFEC inspection: The procedures describe doing a detailed inspection for cracks in the adjacent skin panel and Station 2598 of the horizontal stabilizer pivot bulkhead structure. If any crack is found in the skin panel or bulkhead structure, the crack may be repaired as specified in the 747 structural repair manual, or contact Boeing for repair data and repair. After the repair is installed, the longeron is replaced with a new longeron.
• If no crack is found during the surface HFEC inspection: The procedures describe doing an open hole HFEC inspection of the longeron for cracks at the specified fastener hole locations.
• If any crack is found during the open hole HFEC inspection: The procedures describe oversizing any cracked hole to remove the crack, and the inspection is repeated for any remaining cracks. If any crack remains after oversizing the hole to the maximum allowed diameter, the longeron is removed and a detailed inspection is done for cracks in the adjacent skin panel and Station 2598 of the horizontal stabilizer pivot bulkhead structure. If any crack is found in the skin panel or bulkhead structure, the crack is repaired as specified in the 747 structural repair manual, or the procedures recommend contacting Boeing for repair data and repair. After the repair is installed, the longeron is replaced with a new longeron. If no crack is found, a new longeron is installed.

The compliance times for the actions in the service bulletin are as follows:

• The compliance time for the initial surface HFEC inspection is before the accumulation of 20,000 total flight cycles, or within 1,500 flight cycles after the date on the service bulletin, whichever occurs later. If a new longeron is installed, the inspection is repeated before the accumulation of 20,000 flight cycles after the installation. If a longeron is repaired, or if no crack is found during the surface and open hole HFEC inspections, the applicable inspection is repeated at intervals not to exceed 3,000 flight cycles after the repair is done.

The related investigative and corrective actions are to be done before further flight after the surface HFEC inspections are done. The above compliance times and actions apply to the left and right side longerons, independently.

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 same type design. This proposed AD 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 the Proposed AD and Service Information

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.

Costs of Compliance

We estimate that this proposed AD would affect 165 airplanes of U.S. registry. We also estimate that it would take 3 work-hours per product to comply with this proposed AD. The average labor rate is $80 per work-hour. Based on these figures, we estimate the cost of this proposed AD to the U.S. operators to be $39,600, or $240 per product.

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
• 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-2008-0612; Directorate Identifier 2008-NM-059-AD.

Comments Due Date

(a) We must receive comments by July 21, 2008.

Affected ADs

(b) None.

Applicability

(c) This AD applies to all Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747-400D, 747-400F, 747SR, and 747SP series airplanes, certificated in any category.

Unsafe Condition

(d) This AD results from a report of a crack found in the right-side Stringer 11 longeron horizontal flange, adjacent to the horizontal stabilizer pivot bulkhead, during a routine maintenance inspection. We are issuing this AD to detect and correct fatigue cracking of the longeron, which can propagate and cause damage to the adjacent horizontal stabilizer pivot bulkhead. This damage could result in loss of structural integrity and consequent inability of the bulkhead to carry flight loads, which could adversely affect controllability of the airplane.

Compliance

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

Inspection/Related Investigative and Corrective Actions

(f) Except as provided by paragraph (g) of this AD: At the applicable times specified in paragraph 1.E. of Boeing Alert Service Bulletin 747-53A2703, dated February 14, 2008, do a surface high frequency eddy current (HFEC) inspection for cracks in the left- and right-side Stringer 11 longeron exposed surfaces and edges between Station 2598 and 2607 adjacent to the horizontal stabilizer pivot bulkhead; and do all applicable related investigative and corrective actions before further flight, in accordance with the Accomplishment Instructions of the service bulletin, except as provided by paragraph (h) of this AD.

Exception to Compliance Times

(g) Where Boeing Alert Service Bulletin 747-53A2703, dated February 14, 2008, specifies counting the compliance time from “. . . the date on this service bulletin,” this AD requires counting the compliance time from the effective date of this AD.

Exception to Corrective Actions

(h) If any crack is found during any inspection required by this AD, and Boeing Alert Service Bulletin 747-53A2703, dated February 14, 2008, specifies to contact Boeing for appropriate action: Before further flight, repair 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, ATTN: Ivan Li, 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, to make those findings. For a repair method to be approved, the repair must meet the certification basis of the airplane.

Issued in Renton, Washington, on May 29, 2008.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.