E7-20468. Airworthiness Directives; Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 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 inspecting to detect cracking in certain lower lobe fuselage skin lap joints, doing repetitive inspections for cracking at certain fastener locations having countersunk fasteners, and replacing countersunk fasteners with protruding head fasteners at certain fastener locations. This proposed AD would replace a previous high-frequency eddy current (HFEC) inspection method with a new HFEC inspection method, add a one-time inspection for cracking of certain airplanes, and terminate the adjustment factor for the inspection compliance times based on cabin differential pressure. This proposed AD also would include inspection at an additional lap joint. This proposed AD results from reports of fuselage skin cracks found at certain countersunk fastener locations in the upper row of lap joints near the wing-to-body fairings, and from a report that the presence of alodine-coated rivets could cause faulty results during the required inspections using the optional sliding probe HFEC inspection method specified in the existing AD. We are proposing this AD to prevent reduced structural integrity of the fuselage.

DATES:

We must receive comments on this proposed AD by December 3, 2007.

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-2007-0043; Directorate Identifier 2007-NM-058-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

On July 13, 1994, we issued AD 94-15-06, amendment 39-8977 (59 FR 37659, July 25, 1994), for certain Boeing Model 747 series airplanes. That AD requires inspections to detect cracking in certain lower lobe fuselage skin lap joints; doing repetitive inspections for cracking at certain fastener locations having countersunk fasteners; and replacing countersunk fasteners with protruding head fasteners at certain fastener locations. That AD resulted from reports of cracking of the fuselage skin in certain areas and findings of additional countersunk fasteners. We issued that AD to prevent reduced structural integrity of the fuselage.

Actions Since Existing AD Was Issued

In 1985, Boeing started installing aluminum rivets coated with alodine in fuselage skins during production and supplied them to operators in modification kits. Alodine coating on aluminum rivets increases the rivet/skin 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 high frequency eddy current (HFEC) inspection, which was an optional inspection method specified by AD 94-15-06. The effects of these increases in rivet/skin electricity conductivity could be strong enough to mask a crack indication during the required inspections using the optional sliding probe HFEC inspection method specified in AD 94-15-06.

Boeing has informed us that airplanes with line numbers 630 through 814 inclusive could have alodine-coated aluminum rivets installed in the fastener holes that were required to be inspected in accordance with AD 94-15-06. The presence of these rivets could cause faulty results when performing the required inspections using the optional sliding probe HFEC skin inspection method. Consequently, Boeing has issued Boeing Alert Service Bulletin 747-53A2312, Revision 3, dated February 8, 2007. (In AD 94-15-06, we referred to Boeing Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992, as the appropriate source of service information for doing the required actions.) Revision 3 of the alert service bulletin updates the sliding probe HFEC skin inspection method, and includes a one-time special HFEC or detailed inspection of the affected fastener holes for airplanes on which the modification required by AD 94-15-06 has not been accomplished and on which the optional sliding probe HFEC inspection method was used during the last skin inspection. The sliding probe HFEC inspection specified in the previous revisions of the service bulletin would no longer be allowed in this proposed AD.

In addition, paragraph (e)(2) of AD 94-15-06 did not include the lap joint at stringer location S-46L in the list of lap joints requiring inspection for Model 747SP series airplanes. This proposed AD would include that stringer location.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 747-53A2312, Revision 3, dated February 8, 2007. The procedures in Revision 3 of the alert service bulletin are similar to those in Revision 2, dated October 8, 1992. However, Revision 3 changes the instructions for the optional sliding probe HFEC inspection method and also gives instructions for a special (one-time) inspection for cracking of airplanes that were not previously modified according to the service bulletin and on which the sliding probe HFEC inspection method was used during the last skin inspection, and repair if necessary. 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 94-15-06 and would retain certain requirements of the existing AD. This proposed AD would also require accomplishing the additional actions specified in the alert service bulletin described previously, except as discussed under “Differences Between the Proposed AD and the Alert Service Bulletin.”

Differences Between the Proposed AD and the Alert Service Bulletin

Although the alert service bulletin specifies to submit certain information to the manufacturer, this proposed AD does not include that requirement.

The service bulletin specifies to contact the manufacturer for appropriate action, but this proposed AD would require inspection or repairing those conditions, as applicable, 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

This proposed AD would retain certain requirements of AD 94-15-06. Paragraphs (c) and (d) of that AD specify that it is not necessary to count flight cycles at 2.0 psi or less cabin differential pressure; and that for Boeing Model 747SR airplanes, the modification compliance times specified in paragraphs (a) and (b) of that AD may be multiplied by a 1.2 adjustment factor. We find that insufficient data exist to support these adjustments. Consequently, this proposed AD would no longer allow for these adjustment factors. This change has been coordinated with Boeing.

In addition, since AD 94-15-06 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 94-15-06	Corresponding requirement in this proposed AD
Paragraph (a)	Paragraph (f).
Paragraph (b)	Paragraph (g).
Paragraph (c)	Paragraph (h).
Paragraph (d)	Paragraph (i).
Paragraph (e)	Paragraph (j).
Paragraph (f)	Paragraph (k).
Paragraph (g)	Paragraph (l).
Paragraph (h)	Paragraph (m).
Paragraph (i)	Paragraph (n).
Paragraph (j)	Paragraph (o).
Paragraph (k)	Paragraph (p).

Costs of Compliance

This proposed AD would affect about 348 airplanes in the worldwide fleet; 90 of those airplanes are of U.S. registry. The issue associated with alodine-coated aluminum rivets affects 162 airplanes in the worldwide fleet and 24 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	Number of affected airplanes	Cost per airplane	Fleet cost
Inspections (required by AD 90-10-07 and retained in AD 94-15-06 and this AD)	14	$0	90	$1,120, per inspection cycle	$100,800, per inspection cycle.
Inspections (required by AD 94-15-06 and retained in this proposed AD)	82	$0	90	$6,560, per inspection cycle	$590,400, per inspection cycle.
Modification (required by AD 94-15-06 and retained in this proposed AD)	124	Minimal	90	$9,920	$892,800.
One-time inspection (new proposed action)	4	$0	24	$320	$7,680.

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 39-8977 (59 FR 37659, July 25, 1994) and adding the following new airworthiness directive (AD):

Boeing: Docket No. FAA-2007-0043; Directorate Identifier 2007-NM-058-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by December 3, 2007.

Affected ADs

(b) This AD supersedes AD 94-15-06.

Applicability

(c) This AD applies to Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747SR, and 747SP series airplanes, certificated in any category, as identified in Boeing Alert Service Bulletin 747-53A2312, Revision 3, dated February 8, 2007.

Unsafe Condition

(d) This AD results from reports of fuselage skin cracks found at certain countersunk fastener locations in the upper row of lap joints near the wing-to-body fairings, and from a report that the presence of alodine-coated rivets could cause faulty results during the required inspections using the optional sliding probe HFEC inspection method specified in AD 94-15-06. We are issuing this AD to prevent reduced structural integrity of the fuselage.

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.

Requirements of AD 94-15-06

Inspections for Airplanes Having Line Numbers 201 Through 765 Inclusive

(f) For airplanes having line numbers 201 through 765 inclusive: Conduct a high frequency eddy current (HFEC) inspection to detect cracking of the lower lobe lap joints in the vicinity of the wing-to-body fairings, in accordance with Boeing Alert Service Bulletin 747-53A2312, dated June 12, 1989; Revision 1, dated March 29, 1990; Revision 2, dated October 8, 1992; or Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD; at the time specified in paragraph (f)(1), (f)(2), (f)(3), or (f)(4) of this AD, as applicable. As of the effective date of this AD, only Revision 3 shall be used. Repeat this inspection thereafter at intervals not to exceed 4,000 landings until the inspection required by paragraph (j) of this AD is accomplished.

(1) For airplanes that have accumulated less than 11,200 total landings as of February 5, 1990 (the effective date of AD 90-01-07, amendment 39-6440, which was superseded by AD 94-15-06): Prior to the accumulation of 11,000 total landings, or within the next 1,000 landings after February 5, 1990, whichever occurs later.

(2) For airplanes that have accumulated 11,200 or more total landings but less than 15,201 total landings as of February 5, 1990: Within the next 1,000 landings after February 5, 1990, or prior to the accumulation of 15,500 total landings, whichever occurs earlier.

(3) For airplanes that have accumulated 15,201 or more total landings but less than 18,200 total landings as of February 5, 1990: Within the next 300 landings after February 5, 1990, or prior to the accumulation of 18,250 total landings, whichever occurs earlier.

(4) For airplanes that have accumulated 18,200 or more landings as of February 5, 1990: Within the next 50 landings after February 5, 1990.

Repair and Modification for Airplanes Having Line Numbers 201 Through 765 Inclusive

(g) For airplanes having line numbers 201 through 765 inclusive: Accomplish the requirements of paragraphs (g)(1) and (g)(2) of this AD.

(1) If any cracking is detected during the inspections required by paragraph (f) of this AD, prior to further flight, repair in accordance with Boeing Alert Service Bulletin 747-53A2312, dated June 12, 1989; Revision 1, dated March 29, 1990; Revision 2, dated October 8, 1992; or Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD. As of the effective date of this AD, only Revision 3 shall be used.

(2) Prior to the accumulation of 20,000 total landings or within the next 3,000 landings after February 5, 1990 (the effective date of AD 90-01-07), whichever occurs later, modify the airplane by replacing countersunk fasteners in the upper row of the lower lobe lap joints in the vicinity of the wing-to-body fairings with protruding head fasteners, in accordance with the procedures described in Boeing Alert Service Bulletin 747-53A2312, dated June 12, 1989; Revision 1, dated March 29, 1990; Revision 2, dated October 8, 1992; or Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD. As of the effective date of this AD, only Revision 3 shall be used.

Adjustments for Cabin Differential Pressure for Airplanes Having Line Numbers 201 Through 765 Inclusive

(h) For airplanes having line numbers 201 through 765 inclusive: Before the effective date of this AD, for purposes of complying with paragraphs (f) and (g) of this AD, the number of landings may be determined to equal the number of pressurization cycles where the cabin pressure differential was greater than 2.0 psi.

(i) For airplanes having line numbers 201 through 765 inclusive: Before the effective date of this AD, for Model 747SR series airplanes only, based on continued mixed operation of lower cabin differentials, the inspection and modification compliance times specified in paragraphs (f) and (g) of this AD may be multiplied by a 1.2 adjustment factor.

General Visual Inspection for Countersunk Fasteners for All Airplanes

(j) For all airplanes: Prior to the accumulation of 11,000 total landings, or within 1,000 landings after August 24, 1994 (the effective date of AD 94-15-06), whichever occurs later, conduct a general visual inspection, unless previously accomplished within the last 3,000 landings prior to August 24, 1994, to determine if countersunk fasteners have been installed in the lap joints listed in paragraph (j)(1) or (j)(2) of this AD, as applicable, in accordance with the procedures described in Boeing Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992; or Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD. As of the effective date of this AD, only Revision 3 shall be used. Accomplishment of this inspection terminates the inspection requirements of paragraph (f) of this AD.

(1) For Model 747-100, -200, -300, -400, and 747SR series airplanes: From body stations (BS) 741 to 1000 at Stringers (S-)34L, S-34R, S-39L, S-39R, S-44L, and S-44R, and from BS 1480 to 1741 at S-34L, S-34R, S-40L, and S-40R.

(2) For Model 747SP series airplanes: From BS 520 to 1000 at S-34L, S-34R, S-39L, S-39R, S-44L, and S-44R, and from BS 1480 to 1741 at S-34L, S-34R, S-40L, and S-40R.

Corrective Action for Countersunk Fasteners for All Airplanes

(k) For all airplanes: If no countersunk fastener is found in the upper row of a lap joint during the inspection required by paragraph (j) of this AD, no further action is required by this AD for that lap joint.

(l) For all airplanes: If any countersunk fastener is found in the upper row of a lap joint during the inspection required by paragraph (j) of this AD, prior to further flight, perform a high frequency eddy current (HFEC) inspection to detect cracking at all fastener locations in the lap joint where a countersunk fastener was found, in accordance with the procedures described in Boeing Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992; or Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD. As of the effective date of this AD, only Revision 3 shall be used.

Repetitive Inspections

(m) If no cracking is detected during any inspection required by paragraphs (l) and (q) of this AD, at any fastener location where a countersunk fastener was found, repeat the HFEC inspection thereafter at intervals not to exceed 4,000 landings, in accordance with the procedures described in Boeing Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992; or Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD. As of the effective date of this AD, only Revision 3 shall be used. As an alternative to the HFEC inspection, operators may perform a detailed inspection to detect cracking at any fastener location where a countersunk fastener was found, in accordance with the procedures described in Boeing Service Bulletin 747-53A2312, Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD. Perform the detailed inspection within the next 4,000 landings after the HFEC inspection required by paragraph (l) of this AD, and repeat the inspection thereafter at intervals not to exceed 500 landings. At any of the subsequent inspection cycles, operator may use either inspection method provided that the corresponding inspection interval is used to determine the compliance time of the next inspection.

(n) If cracking is detected during any inspection required by paragraph (l), (m), (p), or (q) of this AD, at any fastener location where a countersunk fastener was found, prior to further flight, repair and modify that lap joint in accordance with Boeing Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992; or Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD. As of the effective date of this AD, only Revision 3 shall be used. Accomplishment of this repair and modification terminates the repetitive inspections required by paragraph (m) of this AD for that lap joint.

Modification of Countersunk Fasteners for All Airplanes

(o) For all airplanes: Prior to the accumulation of 20,000 total landings or within 1,000 landings after August 24, 1994, whichever occurs later, modify all fastener locations where a countersunk fastener was found during the inspections required by paragraph (j) of this AD, in accordance with the procedures described in Boeing Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992; or Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD. As of the effective date of this AD, only Revision 3 shall be used. For purposes of complying with the requirements of this paragraph, fastener locations that were previously modified in accordance with paragraph (g) or (n) of this AD do not need to be modified again. Accomplishment of this modification terminates the repetitive inspections required by paragraph (m) of this AD for the modified fastener locations.

Post-Modification Inspections for All Airplanes

(p) For all airplanes: Prior to the accumulation of 10,000 total landings following the modification required by paragraph (g), (n), (o), (q) or (s) of this AD, perform an HFEC inspection to detect cracking at all fastener locations where a countersunk fastener was found, and repeat this inspection thereafter at intervals not to exceed 4,000 landings, in accordance with the procedures described in Boeing Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992; or Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD. As of the effective date of this AD, only Revision 3 shall be used.

New Requirements of This AD

General Visual Inspection for Countersunk Fasteners and Modification for Model 747SP Airplanes at Stringer S-46L

(q) For Model 747SP series airplanes having line numbers 201 through 814 inclusive, do the actions in paragraphs (q)(1) and (q)(2) of this AD at the times specified in those paragraphs.

(1) Prior to the accumulation of 11,000 total landings, or within 1,000 landings as of the effective date of this AD, whichever occurs later, unless previously accomplished within the last 3,000 landings prior to the effective date of this AD, conduct a general visual inspection of the lap joint from BS 520 to 1000 at stringer S-46L to determine if countersunk fasteners have been installed in the specified area, in accordance with the procedures described in Boeing Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992; or Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD.

(i) If no countersunk fastener is found in the upper row of the lap joint during the inspection, no further action is required by this AD for the lap joint.

(ii) If any countersunk fastener is found in the upper row of the lap joint, prior to further flight, perform an HFEC inspection to detect cracking at all fastener locations where a countersunk fastener was found, in accordance with the procedures described in Boeing Service Bulletin 747-53A2312, Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD.

A. If no cracking is found, repeat the inspection thereafter in accordance with the requirements of paragraph (m) of this AD.

B. If any cracking is found, prior to further flight, repair and modify the lap joint as required by paragraph (n) of this AD.

(2) Prior to the accumulation of 20,000 total landings, or within 1,000 landings as of the effective date of this AD, whichever occurs later, modify all fastener locations where a countersunk fastener was found, during the inspection required by paragraph (q)(1) of this AD, in accordance with the Accomplishment Instructions of Boeing Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992; or Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD. For purposes of complying with the requirements of this AD, fastener locations that were previously modified in accordance with paragraph (n) of this AD do not need to be modified again. Accomplishment of this modification terminates the repetitive inspections required by paragraph (m) of this AD for the modified fastener locations.

Adjustments to Compliance Time: Cabin Differential Pressure

(r) For the purposes of calculating the compliance threshold and repetitive intervals for actions required by paragraphs (f) and (g) of this AD, on or as of 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 intervals for the actions required by paragraph (f) of this AD have been calculated in accordance with paragraph (h) and/or (i) of this AD by excluding the number of flight cycles in which cabin differential pressure is at 2.0 pounds psi or less, and/or by using a 1.2 adjustment factor: Continue to adjust the repetitive intervals in accordance with paragraph (h) and/or (i) of this AD until the next inspection required by paragraph (f) of this AD is accomplished. Thereafter, no adjustment to compliance times based on paragraph (h) and/or (i) of this AD is allowed.

Special One-Time Inspection for Cracking of Certain Airplanes

(s) For airplanes with line numbers 630 through 814 inclusive that meet the conditions specified in paragraphs (s)(1) and (s)(2) of this AD: Within 300 flight cycles as of the effective date of this AD, or within 500 flight cycles after the most recent sliding probe inspection done in accordance with Boeing Alert Service Bulletin 747-53A2312, Revision 1, dated March 29, 1990; or Revision 2, dated October 8, 1992, whichever occurs later, do a special one-time HFEC inspection or a special one-time detailed inspection for cracking, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2312, Revision 3, dated February 8, 2007. If any cracking is found in a lap joint, before further flight, repair and modify that lap joint in accordance with Boeing Service Bulletin 747-53A2312, Revision 3, dated February 8, 2007; except as provided by paragraph (u) of this AD. Accomplishment of this repair and modification terminates the repetitive inspections required by paragraph (m) of this AD for that lap joint. This special one-time inspection is not required for lap joints that have been modified in accordance with paragraph (g), (n), (o), or (q) of this AD.

(1) Airplanes that have not been modified in accordance with paragraph (g) or (o) of this AD.

(2) Airplanes on which the sliding probe HFEC inspection method specified in Boeing Service Bulletin 747-53A2312, Revision 1, dated March 29, 1990; or Revision 2, dated October 8, 1992; was used during the last skin inspection required by AD 94-15-06.

Actions After the Special One-Time Inspection if No Cracking Is Found

(t) For airplanes specified in paragraph (s) of this AD on which no cracking is found during the special one-time inspection, do the applicable repetitive inspections specified in paragraph (t)(1) or (t)(2) of this AD.

(1) If the special one-time inspection was done using the HFEC inspection method in accordance with paragraph (s) of this AD, perform the next inspection required by paragraph (m) of this AD within the next 4,000 flight cycles after doing the inspection required by paragraph (s) of this AD, and repeat the inspection thereafter in accordance with paragraph (m) of this AD.

(2) If the special one-time inspection was done using the detailed inspection method in accordance with paragraph (s) of this AD, perform the next inspection required by paragraph (m) of this AD within the next 500 flight cycles after doing the inspection required by paragraph (s) of this AD, and repeat the inspection thereafter in accordance with paragraph (m) of this AD.

Contacting the Manufacturer

(u) Where Boeing Alert Service Bulletin 747-53A2312, Revision 3, dated February 8, 2007 specifies to contact Boeing for appropriate action for a repair or inspection, before further flight, do the applicable action in paragraph (u)(1) or (u)(2) of this AD.

(1) Do the repair using a method approved in accordance with the procedures specified in paragraph (v) of this AD.

(2) Do the inspection using a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the Manager's approval letter must specifically refer to this AD.

Alternative Methods of Compliance (AMOCs)

(v)(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) 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 shall 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.

(4) AMOCs approved previously in accordance with AD 94-15-06, are approved as AMOCs for the corresponding provisions of this AD if the AMOC does not involve using the existing sliding probe HFEC skin inspection method specified in Boeing Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992, or an earlier version. In addition, the provisions of paragraph (r) of this AD must be applied to AMOCs approved previously in accordance with AD 94-15-06, amendment 39-8977, where applicable.

Issued in Renton, Washington, on October 5, 2007.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.