E6-8007. Airworthiness Directives; Boeing Model 747-100, 747-100B, 747-200B, 747-200C, 747-200F, 747SR, and 747SP Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), Department of Transportation (DOT).

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Boeing Model 747 series airplanes. The existing AD currently requires repetitive inspections to detect cracks at certain stringer fastener locations; and repair, if necessary. For certain airplanes, the existing AD requires a modification in certain areas where reports indicate that cracking was prevalent. This modification terminates the repetitive inspections only for those areas, and is also an option for other airplanes affected by the existing AD. This proposed AD would require one-time inspections at a reduced inspection threshold of areas that may have Alodine-coated rivets installed, and repair if necessary. This proposed AD results from a report of cracking discovered in a skin lap joint that was previously inspected using the eddy current method. We are proposing this AD to prevent rapid decompression of the airplane due to disbonding and subsequent cracking of the skin panels.

DATES:

We must receive comments on this proposed AD by July 10, 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 service information identified in this proposed AD.

FOR FURTHER INFORMATION CONTACT:

Nicholas Kusz, 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 “Docket No. FAA-2006-24877; Directorate Identifier 2005-NM-253-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 the DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or may can 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

On December 3, 1990, we issued AD 90-26-10, amendment 39-6836 (55 FR 51401, December 14, 1990), for certain Boeing Model 747 series airplanes. That AD requires repetitive inspections to detect cracks at certain stringer fastener locations; and repair, if necessary. For certain airplanes, AD 90-26-10 requires a modification in certain areas where reports indicate that cracking was prevalent. This modification terminates the repetitive inspections only for those areas. That AD resulted from reports of multiple longitudinal skin cracks. We issued that AD to prevent rapid decompression of the airplane.

Actions Since Existing AD Was Issued

Since 1985, Boeing has incorporated rivets coated with Alodine into production fuselage aluminum skins and post-production skin modification kits. Alodine coating on rivets provides a protective chemical conversion coating, but also increases electrical conductivity. Certain non-destructive inspection (NDI) methods rely on disruptions in the electromagnetic field around cracks in metallic structures to detect cracking. One such NDI method is the sliding probe eddy current inspection, which was one inspection method required by AD 90-26-10. Conductivity of the Alodine-coated rivet could be strong enough to mask cracking in the fastener hole during eddy current inspections.

Since we issued AD 90-26-10, cracking was discovered in a skin lap joint that was previously inspected using the eddy current method. The cracking was discovered during a full-scale fatigue test on a Model 737 fuselage. The skin lap joints on Model 737 airplanes are similar to those on the affected Model 747 airplanes.

The manufacturer has accomplished a comprehensive study of the effect of Alodine-coated rivets on all Boeing Airplane models. Based on the critical nature of the sliding probe eddy current inspection method, this study indicates that two existing ADs, AD 96-23-02 and AD 90-26-10, require further rulemaking. We are proposing this NPRM to supersede AD 90-26-10, and Docket No. FAA-2006-24865 to supersede AD 96-23-02. In addition, based on this study, the FAA does not propose to issue other ADs related to Alodine-coated rivets.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 747-53A2321, Revision 7, dated October 27, 2005 (the original issue of Boeing Alert Service Bulletin 747-53A2321, dated October 31, 1989, was referenced as the appropriate source of service information for accomplishing the required actions in AD 90-26-10). Revision 7 of the alert service bulletin describes the procedures that were required by AD 90-26-10, and includes new procedures for a one-time external detailed inspection for cracking of the skin area between the lap joints between stringer 6 and stringer 14, from body station 340 to 520, which is designated as Area 1 by the original issue of Boeing Alert Service Bulletin 747-53A2321; and a new external high-frequency eddy current inspection to ensure a thorough inspection for cracking of the areas where Alodine-coated rivets are installed. Alodine-coated rivets may have been installed within Area 1 during accomplishment of a modification specified in Boeing Service Bulletin 747-53-2275, which was mandated by AD 90-06-06, amendment 39-6490 (55 FR 8374, March 7, 1990). The modification installed external doublers in a small portion of Area 1 and also replaced stringers throughout Area 1. The fasteners used for the stringer replacement and doubler installation may have been Alodine-coated rivets. However, the service bulletin excludes from this inspection those areas covered by the modification doublers. 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 develop on other airplanes of the same type design. For this reason, we are proposing this AD, which would supersede AD 90-26-10 and would retain the requirements of the existing AD. This proposed AD would also require accomplishing the actions specified in the alert service bulletin described previously, except as discussed under “Difference Between the Proposed AD and the Alert Service Bulletin.”

Difference Between the Proposed AD and the Alert Service Bulletin

Boeing Alert Service Bulletin 747-53A2321, Revision 7, 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.

Changes to Existing AD

Paragraphs E. and F. of AD 90-26-10 allow for adjustment to the compliance threshold by not counting the flight cycles in which cabin differential pressure is at 2.0 pounds per square inch (psi) or less; or allow for multiplication by an adjustment factor based on continued mixed operation at lower cabin pressure differentials. This proposed AD would not allow those adjustments. However, this proposed AD states that operators may continue to adjust the repetitive inspection interval based on a lower cabin differential pressure until the next scheduled inspection. Thereafter, this proposed AD would not allow such adjustment. We have determined that an adjustment of flight cycles due to a lower cabin differential pressure is not substantiated and will not be allowed for use in determining the flight-cycle threshold for this proposed AD. There have been several instances on other in-service issues where analytical rationales have indicated that pressurization cycles of less than 2.0 psi should not be counted. However, when fleet records have been examined, the airplanes engaged in such operations have the same or greater occurrences of crack findings compared with those on which all pressurized flights are counted. As a result, we consider such matters based on all available factors, including individual operators' specific maintenance programs, technical rationale, and fleet experience. We have found that such provisions are applicable only to a small number of operators that may not pressurize their airplanes above 2.0 psi in all their flights. We have determined that the best way to handle such circumstances is for operators to request an AMOC in accordance with the procedures in paragraph (n) of this proposed AD, rather than by increasing the complexity of the AD by addressing each operator's unique situation.

Boeing has received a Delegation Option Authorization (DOA). We have revised this proposed AD to delegate the authority to approve an alternative method of compliance for any repair that would be required by this proposed AD to the Authorized Representative for the Boeing DOA Organization.

The “detailed visual inspection” specified in AD 90-26-10 is referred to as a “detailed inspection” in this proposed AD. We have included the definition for a detailed inspection in a note in the proposed AD.

We have revised the applicability to identify the model designations as published in the most recent type certificate data sheet for the affected model.

This proposed AD would retain certain requirements of AD 90-26-10. Since AD 90-26-10 was issued, the AD format has been revised, and certain Paragraphs have been rearranged. As a result, the corresponding Paragraph identifiers have changed in this proposed AD, as listed in the following table:

Revised Paragraph Identifiers

Requirement in AD 90-26-10	Corresponding requirement in this proposed AD
Paragraph A	Paragraph (f).
Paragraph C	Paragraph (g).
Paragraph D	Paragraph (h).
Paragraph E	Paragraph (i).
Paragraph F	Paragraph (j).

Costs of Compliance

There are about 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. This proposed AD would affect about 59 airplanes of U.S. registry. The average labor rate is $80 per work hour.

Estimated Costs

Action	Work hours	Parts	Cost per airplane	Fleet cost
Inspection (required by AD 90-26-10)	48	None	$3,840, per inspection cycle	$226,560, per inspection cycle.
Modification (required by AD 90-26-10)	620	69, 246	118,846	7,011,914.
Inspection (new proposed action)	48	None	3,840, per inspection cycle	226,560, 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 removing amendment 39-6836 (55 FR 51401, December 14, 1990) and adding the following new airworthiness directive (AD):

Boeing: Docket No. FAA-2006-24877; Directorate Identifier 2005-NM-253-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by July 10, 2006.

Affected ADs

(b) This AD supersedes AD 90-26-10.

Applicability

(c) This AD applies to Boeing Model 747-100, 747-100B, 747-200B, 747-200C, 747-200F, 747SR, and 747SP series airplanes, certificated in any category; line numbers 001 through 430 inclusive.

Unsafe Condition

(d) This AD results from a report of cracking discovered in a skin lap joint that was previously inspected using the eddy current method. We are issuing this AD to prevent rapid decompression of the airplane due to disbonding and subsequent cracking of the skin panels.

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.

Restatement of Certain Requirements of AD 90-26-10

Inspections

(f) Prior to the accumulation of 12,000 flight cycles or within the next 1,000 flight cycles after January 22, 1991 (the effective date of AD 90-26-10), whichever occurs later, unless previously accomplished within the last 1,000 flight cycles, conduct an external detailed and external high frequency eddy current (HFEC) inspection for cracks of the fuselage skin from body station (BS) 220 to BS 520, left and right hand side of the airplane between stringers (S)-6 and S-14, excluding the skin lap joints, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2321, dated October 31, 1989; or Revision 7, dated October 27, 2005. After the effective date of this AD, only Revision 7 may be used. Doing the inspections in this paragraph in accordance with Revision 7 of the service bulletin eliminates the need for doing the actions in paragraph (k) of this AD. Repeat the inspections thereafter at intervals not to exceed 2,000 flight cycles until the terminating modification in paragraph (g) of this AD is done, except as provided by paragraph (h) of this AD.

Note 1:

For the purposes of this AD, a detailed inspection is: “An intensive examination of a specific item, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at an intensity deemed appropriate. Inspection aids such as mirror, magnifying lenses, etc., may be necessary. Surface cleaning and elaborate procedures may be required.”

Terminating Modification

(g) For airplanes line numbers 001 through 200, prior to the accumulation of 20,000 total flight cycles, or within 48 months after January 22, 1991, whichever occurs later: Perform the terminating modification of the skin panel from BS 340 to BS 520, S-6 to S-14, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2321, dated October 31, 1989; or Revision 7, dated October 27, 2005. After the effective date of this AD, only Revision 7 may be used. The modification consists of replacing the skin panel with a new skin panel which was manufactured utilizing the improved hot phosphoric anodize bonding process.

(h) Replacement of the skin panel required by paragraph (g) of this AD constitutes terminating action for the inspections from BS 340 to BS 520 required by paragraphs (f) and (k) of this AD. The inspections from BS 220 to BS 340 required by paragraph (f) of this AD are to be continued.

Adjustments for Cabin Differential Pressure

(i) Before the effective date of this AD: Flight cycles conducted at 2.0 pounds per square inch (psi) or less cabin differential pressure need not be counted for the purpose of this airworthiness directive.

(j) Before the effective date of this AD: For Model 747SR airplanes only, the threshold and repetitive inspection intervals specified herein may be multiplied by the 1.2 adjustment factor based on continued mixed operation at lower cabin pressure differentials.

New Requirements of This AD

Inspections of Skins With Alodine-Coated Rivets

(k) For airplanes identified in Figure 9 of the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2321, Revision 7, dated October 27, 2005, as requiring additional inspection: Within 150 flight cycles after the effective date of this AD, do the inspection in paragraph (k)(1) or (k)(2) of this AD in accordance with the Accomplishment Instructions of the service bulletin.

(1) Do an external detailed inspection for cracking of Area 1, and repeat the inspection thereafter at intervals not to exceed 150 flight cycles until one of the actions in paragraph (k)(1)(i), (k)(1)(ii), or (k)(1)(iii) is accomplished. Repeat the inspection of Area 1 thereafter in accordance with the requirements of paragraph (f) of this AD.

(i) The inspection in accordance with paragraph (k)(1) of this AD has been done seven times at intervals not to exceed 150 flight cycles. If this option is used: Within 150 flight cycles after the seventh inspection, do the inspection required by paragraph (k)(2) of this AD.

(ii) The inspection in accordance with paragraph (k)(2) has been accomplished.

(iii) The inspections in accordance with paragraph (f) of this AD has been accomplished once in accordance with Revision 7 of the service bulletin.

(2) Do an external HFEC inspection for cracking of Area 1 in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2321, Revision 7, dated October 27, 2005. Repeat the HFEC inspection of Area 1 thereafter in accordance with the requirements of paragraph (f) of this AD.

Repair

(l) If any crack is found during any inspection required by this AD: Before further flight, repair in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2321, dated October 31, 1989; or Revision 7, dated October 27, 2005. After the effective date of this AD, only Revision 7 of the service bulletin may be used. Where Revision 7 of the service bulletin specifies to contact Boeing for repair instructions: Before further flight, repair using a method approved in accordance with the procedures specified in paragraph (n) of this AD.

Adjustments to Compliance Time: Cabin Differential Pressure

(m) For the purposes of calculating the compliance threshold and repetitive interval for actions required by paragraph (f), (g), and (k) of this AD, on or after the effective date of this AD: All flight cycles, including the number of flight cycles in which cabin differential pressure is at 2.0 psi or less, must be counted when determining the number of flight cycles that have occurred on the airplane, and a 1.2 adjustment factor may not be used. However, for airplanes on which the repetitive interval for the actions required by paragraphs (f) and (k) of this AD have been calculated in accordance with paragraph (i) or (j) of this AD by excluding the number of flight cycles in which cabin differential pressure is at 2.0 pounds psi or less, or by using a 1.2 adjustment factor: Continue to adjust the repetitive interval in accordance with paragraph (i) or (j) of this AD until the next inspections required by paragraph (f) or (k) of this AD are accomplished. Thereafter, no adjustment to compliance times based on paragraph (i) or (j) of this AD is allowed.

Alternative Methods of Compliance (AMOCs)

(n)(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) 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.

(4) AMOCs approved previously in accordance with AD 90-26-10 are acceptable for compliance with the requirements of this AD, provided that any alternative terminating action was not based upon inspection results using sliding probe low-frequency eddy current (LFEC), sliding probe HFEC, or mid-frequency eddy current (MFEC) inspection method; and provided that any alternative method future inspections did not incorporate sliding probe LFEC or MFEC inspection method.

Issued in Renton, Washington, on May 16, 2006.

Kevin M. Mullin,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.