E6-5469. Airworthiness Directives; Boeing Model 737-100, -200, and -200C 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 737 series airplanes. The existing AD currently requires inspection of the elevator tab inboard hinge support structure to detect fatigue cracking and corrective action if necessary. That AD also provides an optional terminating action. This proposed AD would add airplanes to the applicability and would require new repetitive inspections. For airplanes having elevators with laminated rear spars, this proposed AD would require repetitive inspections for interlaminar corrosion, delamination, or disbonding in the rear spar, repetitive inspections for cracking in the spar web, and repair including related investigative/corrective actions if necessary. For airplanes having elevators with solid rear spars, this proposed AD would require repetitive inspections for cracking in the spar web and repair including related investigative/corrective actions if necessary. This proposed AD results from reports of cracks in the elevator rear spar web at the tab hinge bracket locations. We are proposing this AD to detect and correct cracking, corrosion, interlaminar corrosion, delamination, and disbonding in the elevator rear spar, which may reduce elevator stiffness and lead to in-flight vibration. In-flight vibration may lead to elevator and horizontal stabilizer damage and reduced controllability of the airplane.

DATES:

We must receive comments on this proposed AD by May 30, 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:

Nancy Marsh, 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-2006-24432; Directorate Identifier 2005-NM-227-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 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 June 7, 1989, we issued AD 76-11-05 R1, amendment 39-6234 (54 FR 25709, June 19, 1989), for certain Boeing Model 737 series airplanes. That AD requires repetitive inspections of the elevator tab inboard hinge support structure to detect fatigue cracking and corrective action if necessary. That AD also provides an optional terminating action. That AD resulted from the determination that additional airplanes were manufactured to the same design as airplanes identified in AD 76-11-05 and are subject to the same failure. We issued that AD to detect fatigue cracking, which could result in vibration and possible flutter.

Other Relevant Rulemaking

On January 16, 1990, we issued AD 90-06-02, amendment 39-6489 (55 FR 8372, March 7, 1990), applicable to certain Boeing Model 737 series airplanes, which would require incorporation of certain structural modifications. That AD refers to Boeing Document D6-38505, Revision C, dated December 11, 1989, “Aging Airplane Service Bulletin Structural Modification Program—Model 737-100/-200/-200C,” which references Boeing Service Bulletins 737-55A1020 and 737-55-1022 for certain modifications. We issued that AD to prevent structural failure.

Actions Since Existing AD Was Issued

Since we issued AD 76-11-05 R1, we have received reports of cracks in the elevator rear spar web at the tab hinge bracket locations, on Model 737-100, -200, and -200C series airplanes. These airplanes had 6,100 to 56,000 total flight hours and 2,400 to 66,000 total flight cycles. Some airplanes had modifications and repairs done in accordance with Boeing Service Bulletins 737-55A1020 and 737-55-1022. Accomplishing the actions specified in Section III, Part II, including installation of the bolt retainer clips, of Boeing Alert Service Bulletin 737-55A1020, Revision 1, dated August 20, 1976; Revision 2, dated February 11, 1977; or Revision 3, dated December 22, 1988; or the preventive modification specified in Section III, Part II of Boeing Service Bulletin 737-55-1022, dated April 15, 1977; are terminating action for AD 76-11-05 R1 and required modifications for AD 90-06-02, amendment 39-6489. Because cracking has continued to occur, the actions described in Boeing Service Bulletins 737-55A1020 and 737-55-1022 do not eliminate the need for repetitive inspections for cracking.

Analysis shows that the cracks in the elevator rear spar web are caused by deflection stresses. Excessive web cracking at multiple locations will reduce the elevator support stiffness. The reduced stiffness will lead to in-flight vibrations and consequent damage to the elevator and horizontal stabilizer. This condition, if not corrected, could result in reduced controllability of the airplane.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 737-55A1078, dated October 27, 2005, which replaces Boeing Service Bulletins 737-55A1020 and 737-55-1022. Boeing Alert Service Bulletin 737-55A1078 is referenced as the appropriate source of service information for doing the actions in this proposed AD.

Appendix A of Boeing Alert Service Bulletin 737-55A1078 describes procedures for determining the elevator configuration number or elevator group number of the rear spar. The number indicates if elevators have laminated rear spars or solid rear spars, as well as other configuration differences.

For airplanes having elevators with laminated rear spars, the alert service bulletin describes procedures for repetitive detailed inspections for cracking at hinge bracket locations and for interlaminar corrosion of the rear spar as specified in Part I of the Accomplishment Instructions. For airplanes having elevators with laminated rear spars, the alert service bulletin also describes procedures for repetitive detailed and special detailed inspections for interlaminar corrosion, delamination, and disbonding of the rear spar as specified in Part III of the Accomplishment Instructions.

For airplanes having elevators with solid rear spars, the alert service bulletin describes procedures to do repetitive detailed inspections for cracking at the hinge bracket locations in the spar web as specified in Part II of the Accomplishment Instructions.

For all airplanes, if no cracking or interlaminar corrosion is found during any inspection, the alert service bulletin specifies to install a hinge bolt retainer clip if necessary.

For all airplanes, if any interlaminar corrosion or cracking is found during any inspection, the alert service bulletin specifies to do applicable repairs including related investigative actions and corrective actions as specified in Parts IV through VIII (Interim Repair Options A through D) and Part IX (Time-limited Repair) of the Accomplishment Instructions. Appendix C of the alert service bulletin describes how to determine which interim repair option and time-limited repair can be used. The service bulletin describes the repairs, including related investigative and corrective actions, as follows:

• Part IV—Option A Interim Repair—Spar Splice: The spar splice repair consists of removal of a cracked segment or segments of the elevator rear spar and installation of a new replacement spar segment or segments. The repair includes inspecting holes for signs of loose or damaged fasteners, repair if necessary, and contacting the manufacturer for certain repair instructions. The repair also includes making sure balancing requirements are met for the elevator and the tab after the corrective actions are done.
• Parts V and VI—Option B or D Interim Repair—Spar Replacement Without Replacement of Thin Tee Clips with Thick Tee Clips (for certain elevator configurations): The Option B or D spar replacements consist of removal of the hinge brackets and rear spar ribs from the spar, removal of the existing spar, installation of a new replacement spar, and reinstallation of the hinge brackets and rear spar ribs to the new spar. These spar replacement options include inspecting holes for signs of loose or damaged fasteners, repair if necessary, and contacting the manufacturer for certain repair instructions. These spar replacement options also include making sure balancing requirements are met for the elevator and the tab after the corrective actions are done.
• Parts VII and VIII—Option C Interim Repair—Spar Replacement With Replacement of Thin Tee Clips with Thick Tee Clips (for certain elevator configurations): The Option C spar replacement consists of removal of the hinge brackets, rear spar ribs, and thin tee clips from the spar, removal of the existing spar, installation of a new replacement spar and thick tee clips, and reinstallation of the hinge brackets and rear spar ribs to the new spar. This replacement option includes inspecting holes for signs of loose or damaged fasteners, repairing if necessary, and contacting the manufacturer for certain repair instructions. This replacement option also includes making sure balancing requirements are met for the elevator and tab after the corrective actions are done.
• Part IX—Time-limited Repair: The repair consists of installation of repair components and an eddy current inspection for crack containment at the stop-drilled hole. The repair instructions include contacting the manufacturer if any crack is outside the limit specified in the alert service bulletin. The repair also includes making sure balancing requirements are met for the elevator and tab after the corrective actions are done. If the time-limited repair is done, the alert service bulletin specifies that the Option A or D interim repair must done within 24 months, 2,000 flight hours, or 1,500 flight cycles, whichever occurs first, after the time-limited repair is done.

The alert service bulletin specifies the following compliance times for doing the inspections in paragraph 1.E. Compliance and Appendix B of the alert service bulletin:

• Part I Initial Inspection: Within 1,000 flight hours or 750 flight cycles after the release date of the alert service bulletin, whichever occurs first; or within 2,000 flight hours or 1,500 flight cycles after the release date of the alert service bulletin, whichever occurs first; depending on elevator group number/configuration number.
• Part I Repetitive Inspections: At intervals not to exceed 1,000 flight hours or 750 flight cycles, whichever occurs first; or at intervals not to exceed 2,000 flight hours or 1,500 flight cycles, whichever occurs first; depending on elevator group number/configuration number.
• Part II Initial Inspection: Within 1,000 flight hours or 750 flight cycles after the release date of the alert service bulletin, whichever occurs first; or 2,000 flight hours or 1,500 flight cycles after the release date of the alert service bulletin, whichever occurs first; or 24,000 flight hours or 18,000 flight cycles, whichever occurs first, on the elevator since new or since the modification specified in Boeing Service Bulletin 737-55-1022 has been done, provided it can be positively determined from the operator's records; depending on elevator group number/configuration number.
• Part II Repetitive Inspections: At intervals not to exceed 6,000 flight hours or 4,500 flight cycles, whichever occurs first; or at intervals not to exceed 1,000 flight hours or 750 flight cycles, whichever occurs first; depending on elevator group number/configuration number. For certain elevators, accomplishing any Option C or Option D interim repairs defers the accomplishment of the next Part II inspection to within 24,000 flight hours or 18,000 flight cycles since the repair.
• Part III Initial Inspection: Within 1,000 flight hours or 750 flight cycles, whichever occurs first; or within 2,000 flight hours or 1,500 flight cycles, whichever occurs first; depending on elevator group number/configuration number.
• Part III Repetitive Inspections: At intervals not to exceed 8,000 flight hours or 6,000 flight cycles, whichever occurs first.

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 the Alert Service Bulletin.”

Differences Between the Proposed AD and the Alert Service Bulletin

The alert 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.

Where Table B.4 in Appendix B of the alert service bulletin specifies a compliance time in flight hours or flight cycles, this proposed AD would require the actions specified in Table B.4 be done at the earlier of the compliance times in flight hours or flight cycles.

Clarification of Inspection and Corrective Action

Operators should note that step 3. of Part III of the alert service bulletin specifies to do a special detailed inspection for spar interlaminar corrosion as given in Figure 3. Figure 3 specifies to do a detailed inspection for corrosion and disbonding and a special detailed inspection for interlaminar corrosion and delamination. Thus, in Part III of the alert service bulletin, operators must inspect for interlaminar corrosion, delamination, and disbonding.

Operators should note that Figure 3 of the alert service bulletin also specifies that a spar should be rejected if interlaminar corrosion, delamination, or disbonding is found. However, step 3.a. of Part III of the alert service bulletin only specifies that if interlaminar corrosion is found, spar replacement is required in accordance with Appendix C; step 3.C. of Appendix C of the alert service bulletin specifies that for laminated spars that have interlaminar corrosion, only repair options B, C, and D are permitted. Step 3.a. of Part III of the alert service bulletin and step 3.C. of Appendix C of the alert service bulletin do not specify what to do if delamination or disbonding is found.

Step 3.a. of Part III of the alert service bulletin should have specified that spar replacement is required if interlaminar corrosion, delamination, or disbonding is found. Step 3.C. of Appendix C of the alert service bulletin should have specified that for laminated spars that have interlaminar corrosion, delamination, or disbonding, only repair options B, C, and D are permitted. We have included this clarification in paragraph (o) of this proposed AD.

Explanation of Change to Applicability

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

Correction of Typographical Error for Service Bulletin Date

AD 76-11-05 R1 referred to Boeing Service Bulletin 737-55-1022, Section III, Part II, dated April 15, 1987. However, the service bulletin is dated April 15, 1977. We have fixed this typographical in the service bulletin reference in this proposed AD.

Change to Existing AD

This proposed AD would retain certain requirements of AD 76-11-05 R1. Since AD 76-11-05 R1 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 76-11-05 R1	Corresponding requirement in this proposed AD
Paragraph B	paragraph (f).
Paragraph C	paragraph (g).
Paragraph D	paragraph (h).

Costs of Compliance

There are about 1,355 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.

Estimated Costs

Action	Work hours	Average labor rate per hour	Cost per airplane	Number of U.S.-registered airplanes	Fleet cost
Inspection, per inspection cycle	10-100	$80	$800-$8,000, per inspection cycle	230	$184,000-$1,840,000, 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 39-6234 (54 FR 25709, June 19, 1989) and adding the following new airworthiness directive (AD):

Boeing: Docket No. FAA-2006-24432; Directorate Identifier 2005-NM-227-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by May 30, 2006.

Affected ADs

(b) This AD supersedes AD 76-11-05 R1.

Applicability

(c) This AD applies to Boeing Model 737-100, -200, and -200C series airplanes, certificated in any category; as identified in Boeing Alert Service Bulletin 737-55A1078, dated October 27, 2005.

Unsafe Condition

(d) This AD results from reports of cracks in the elevator rear spar web at the tab hinge bracket locations. We are issuing this AD to detect and correct cracking, corrosion, interlaminar corrosion, delamination, and disbonding in the elevator rear spar, which may reduce elevator stiffness and lead to in-flight vibration. In-flight vibration may lead to elevator and horizontal stabilizer damage and reduced controllability 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.

Restatement of Certain Requirements of AD 76-11-05 R1

(f) For Model 737-100, -200, and -200C series airplanes, line number 001 through 491 inclusive: Within the next 300 hours time-in-service after July 24, 1989 (the effective date of AD 76-11-05 R1), unless accomplished within the last 700 hours time-in-service, and at intervals thereafter not to exceed 1,000 hours time-in-service, conduct the inspection required by paragraph (g) of this AD. Accomplishing the initial inspections specified in paragraph (j) of this AD terminates the requirements of this paragraph.

(g) For Model 737-100, -200, and -200C series airplanes, line number 001 through 491 inclusive: At the times specified in paragraph (f) of this AD, inspect for excessive deflection of the elevator tab, right and left hand, in accordance with the inspection procedures specified in Section III, Part I, paragraphs C. and D., of Boeing Alert Service Bulletin 737-55A1020, Revision 1, dated August 20, 1976; Revision 2, dated February 11, 1977; or Revision 3, dated December 22, 1988. If the elevator tab-to-elevator relative deflection exceeds 1/10 inch, prior to further flight, modify the elevator in accordance with paragraph (h) of this AD. Accomplishing the initial inspections specified in paragraph (j) of this AD terminates the requirements of this paragraph.

(h) For Model 737-100, -200, and -200C series airplanes, line number 001 through 491 inclusive: Installation of one of the modifications specified in Boeing Alert Service Bulletin 737-55A1020, Revision 1, dated August 20, 1976; Revision 2, dated February 11, 1977; or Revision 3, dated December 22, 1988; Section III, Part II, including installation of the bolt retainer clips or the preventive modification specified in Boeing Service Bulletin 737-55-1022, Section III, Part II, dated April 15, 1977; is considered terminating action for the inspection requirements of paragraph (g) of this AD.

New Requirements of This AD

Determine Elevator Group Number or Elevator Configuration Number

(i) Within 1,000 flight hours or 750 flight cycles after the effective date of this AD, whichever occurs first, determine the elevator group number or the elevator configuration number in accordance with Appendix A of Boeing Alert Service Bulletin 737-55A1078, dated October 27, 2005.

Initial and Repetitive Inspections

(j) At the applicable time specified in Tables 2 and 3 of paragraph 1.E. “Compliance” of Boeing Alert Service Bulletin 737-55A1078, dated October 27, 2005, except where the alert service bulletin specifies a compliance time from the release date of the alert service bulletin, this AD requires the compliance time after the effective date of this AD: Do the applicable initial detailed and special detailed inspections for interlaminar corrosion, cracking, delamination, or disbonding in the rear spar by doing all the applicable actions specified in Parts I, II, and III of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-55A1078, dated October 27, 2005; except where step 3. of Part III of the alert service bulletin specifies to do a special detailed inspection for spar interlaminar corrosion as given in Figure 3, this AD requires all actions specified in Figure 3 to be done (a detailed inspection for interlaminar corrosion and disbonding and a special detailed inspection for interlaminar corrosion and delamination). Doing the initial inspections terminates the requirements of paragraphs (f) and (g) of this AD.

(k) Repeat the inspections specified in paragraph (j) of this AD at the applicable time specified in Tables 4 and 5 of paragraph 1.E. “Compliance” of Boeing Alert Service Bulletin 737-55A1078, dated October 27, 2005; except where Table B.4 in Appendix B of the alert service bulletin specifies compliance times in flight hours or flight cycles, this AD requires the actions specified in Table B.4 be done at the earlier of the compliance times in flight hours or flight cycles.

Corrective Actions

(l) If any interlaminar corrosion, cracking, delamination, or disbonding is found during any inspection required by this AD: Before further flight, use Appendix C of Boeing Alert Service Bulletin 737-55A1078, dated October 27, 2005, to determine the permitted repairs, and do the applicable repair, including related investigative and corrective actions, by doing all the applicable actions specified in Parts IV through VIII (Interim Repairs) and Part IX (Time-limited Repair) of the Accomplishment Instructions of the alert service bulletin, except as provided by paragraphs (n) and (o) of this AD.

(m) If the time-limited repair specified in Part IX of the alert service bulletin is done: At the time specified in Table 6 of paragraph 1.E. “Compliance” of Boeing Alert Service Bulletin 737-55A1078, dated October 27, 2005, do the applicable repair, including related investigative and corrective actions, by doing all the applicable actions specified in Parts IV through VI (Interim Repairs). Thereafter, do the repetitive inspections specified in paragraph (k) of this AD.

(n) Where Boeing Alert Service Bulletin 737-55A1078, dated October 27, 2005, specifies to contact the manufacturer for appropriate action for the inspar rib replacement or for more instructions if any crack is outside the limit specified in the service bulletin: Before further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA; or using a method approved in accordance with paragraph (p) of this AD.

(o) Where step 3.a. of Part III of the alert service bulletin specifies that if interlaminar corrosion is found, spar replacement is required, this AD requires spar replacement if interlaminar corrosion, delamination, or disbonding is found. Where step 3.C. of Appendix C of the alert service bulletin specifies that for laminated spars that have interlaminar corrosion, only repair options B, C, and D are permitted, this AD specifies that for laminated spars that have interlaminar corrosion, delamination, or disbonding, only repair options B, C, and D are permitted.

Alternative Methods of Compliance (AMOCs)

(p)(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, and the approval must specifically refer to this AD.

(4) Accomplishing the Interim Repair Option C or D specified in the Accomplishment Instructions of Boeing Alert Service Bulletin 737-55A1078, dated October 27, 2005, is an AMOC for the structural modification requirements specified in paragraph A of AD 90-06-02, amendment 39-6489, that are done in accordance with Boeing Service Bulletins 737-55A1020 or 737-55-1022 only. All provisions of AD 90-06-02 that do not specifically reference these service bulletins remain fully applicable and must be complied with.

(5) AMOCs approved previously in accordance with AD 76-11-05 R1, are approved as AMOCs for the corresponding provisions of paragraphs (f) through (h) of this AD.

Issued in Renton, Washington, on April 3, 2006.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.