E7-17290. Airworthiness Directives; Boeing Model 737-100, -200, -200C, -300, -400, and -500 Series Airplanes

AGENCY:

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

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) for all Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. For certain airplanes, this proposed AD would require replacing the outboard stabilizing fitting and certain adjacent components of the main landing gear (MLG) support beam. This proposed AD would also require repetitive inspections for discrepancies of the outboard stabilizing fitting, walking beam hanger, and rear spar attachment, and corrective actions if necessary. For certain airplanes, this proposed AD would provide an alternative one-time inspection of the outboard stabilizing fitting for discrepancies and corrective actions if necessary, which would extend the compliance time for the replacement of the outboard stabilizing fitting. For certain other airplanes, this proposed AD would also require performing a torque check of the aft pin of the outboard stabilizing fitting, and corrective actions if necessary. This proposed AD results from reports of findings of fatigue cracking of the outboard stabilizing fitting and stress corrosion cracking of the bolts attaching the fitting to the wing rear spar. We are proposing this AD to detect and correct that cracking, which could result in disconnection of the MLG actuator from the rear spar and support beam, and consequent damage to the hydraulic system causing hydraulic fluid leakage and loss of control of the airplane.

DATES:

We must receive comments on this proposed AD by October 15, 2007.

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: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590.
• Fax: [phone].
• Hand Delivery: Room W12-140 on the ground floor of the West Building, 1200 New Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

Contact Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207, for the 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 “FAA-2007-29062; Directorate Identifier 2007-NM-020-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 DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you may 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 Operations office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Operations office (telephone [phone]) is located on the ground floor of the West 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

We have received several reports indicating findings of fatigue cracking of the outboard stabilizing fitting and stress corrosion cracking of the bolts attaching the fitting to the wing rear spar and certain adjacent components of the main landing gear (MLG) support beam on Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. Those reports include the following: Cracking of the outboard stabilizing fitting attributed to fatigue, loose or missing forward pins that attach the stabilizing fitting to the stud assembly; a fractured aft pin that attaches the tube assembly to the aft stabilizing fitting, and fractured H-11 bolts that attach the inboard and outboard stabilizing fittings to the wing rear spar. These failures could result in disconnection of the MLG actuator from the rear spar and support beam, and consequent damage to the hydraulic system fluid supply tube causing hydraulic fluid leakage and loss of control of the airplane.

Other Relevant Rulemaking

On December 30, 1998, we issued AD 98-11-04 R1, amendment 39-10984 (64 FR 987, January 7, 1999), for all Boeing Model 737-100 and -200 series airplanes. That AD supersedes AD 91-14-20 to continue to require that the FAA-approved maintenance program be revised to include inspections that will give no less than the required damage tolerance rating for each Structural Significant Item (SSI). AD 98-11-04 R1 also requires additional and expanded inspections, and repair of cracked structure. That AD was prompted by a structural re-evaluation by the manufacturer which identified additional structural elements where, if damage were to occur, supplemental inspections may be required for timely detection. We issued that AD to ensure the continued structural integrity of the Boeing Model 737-100 and -200 fleet.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 737-57A1266, Revision 1, dated January 3, 2007. For certain airplanes, the service bulletin describes procedures for replacing the outboard stabilizing fitting and certain adjacent components of the MLG support beam. The replacement procedures and configuration group to which the airplane belongs, are as follows.

• For airplanes identified in the service bulletin as Groups 1, 2, 3, 4, and 5, the procedures describe replacing the outboard stabilizing fitting with a new titanium fitting and replacing the H-11 bolts that attach the fitting to the wing rear spar with new Inconel 718 bolts. In addition, the procedures describe replacing the aft pin that attaches the tube assembly to the aft outboard stabilizing fitting with a titanium bolt, replacing the forward pin, and replacing the H-11 bolts for the inboard stabilizing fitting with new Inconel 718 bolts. As part of the replacement of the H-11 bolts, the service bulletin recommends contacting Boeing if corrosion damage is found which cannot be removed. The service bulletin also recommends prior or concurrent accomplishment of Part IV of Boeing Service Bulletin 737-57-1052, Revision 4, dated October 24, 1980, for Group 1 and 3 airplanes. Part IV describes procedures for replacing the existing tube assembly of the MLG support beam with a new assembly. For airplanes that had the aft pin of the aft outboard stabilizing fitting replaced per Boeing Alert Service Bulletin 737-57A1266, dated May 8, 2003, the procedures specify performing a torque check of the aft pin of the aft outboard stabilizing fitting and corrective actions if necessary. If the torque is greater than 570 in. lbs., the corrective action is replacing the aft pin and aft outboard stabilizing fitting. If the torque is less than 570 in. lbs., the corrective action is replacing the aft pin.
• For airplanes identified in the service bulletin as Groups 6 and 7, the procedures describe replacing the outboard stabilizing fitting with a titanium fitting and replacing the H-11 bolts that attach the fitting to the wing rear spar with new Inconel 718 bolts. In addition, the procedures describe replacing the forward pin that attaches the stud assembly to the outboard stabilizing fitting with a titanium pin. The procedures also describe replacing the H-11 bolts for the inboard stabilizing fitting with new Inconel 718 bolts for Group 6 only.
• For airplanes identified in the service bulletin as Group 8, the procedures describe replacing the outboard stabilizing fitting with a titanium fitting, and replacing the forward pin that attaches the stud assembly to the outboard stabilizing fitting with new components.
• For airplanes identified in the service bulletin as Group 9, the procedures describe doing a general visual inspection of the outboard stabilizing fitting and fasteners for discrepancies, and corrective actions if necessary. The corrective action is contacting Boeing if any discrepancies are found.

For airplanes identified in the service bulletin as Group 8, and Groups 1 through 7 on which the existing H-11 bolts were previously replaced with Inconel 718 bolts, the procedures describe an alternative magnetic test of the attach bolts to determine if inspections could be done that may extend the compliance time for the replacement of the outboard stabilizing fitting. If any bolt is magnetic, do not do the alternative inspection. If none of the bolts are magnetic, do a one-time general visual inspection of the stabilizing fitting for discrepancies (damage, failure, or irregularity), and a high frequency eddy current (HFEC) inspection for cracking of the fitting inboard and outboard lug faces, the fillet radii, and the fitting lug hole, and verify the fitting hole is within limits, and corrective actions if necessary. Performing the alternative inspection extends the compliance time from 36 to 60 months for replacing the fitting if no cracking is found.

The corrective actions for the alternative inspections are as follows:

• If cracking is found during the alternative inspection, the service bulletin specifies doing the replacement of the fitting as specified in Part II of the service bulletin. If no cracking is found, the service bulletin specifies doing an installation of replacement bushings and reaming the bushing holes to final size, replacing the forward pin, and for Groups 1 through 5, replacing the aft pin. If any other damage is found or if the fitting hole is beyond the hole size limits, the service bulletin recommends contacting Boeing for repair instructions.

For all airplanes, the service bulletin describes procedures for repetitive inspections for discrepancies of the outboard stabilizing fitting, walking beam hanger, and rear spar attachment fitting, and corrective actions if necessary. The corrective action is contacting Boeing if any discrepancies are found.

Service Bulletin 737-57A1266 refers to the following service bulletins as acceptable sources of service information:

Boeing Service Bulletin 737-57-1231, dated December 1, 1994, is an acceptable source of service information for accomplishment of the replacement of the H-11 attachment bolts of the inboard stabilizing fitting with new components for some airplane groups.

Boeing Service Bulletin 737-57-1073, Revision 4, dated April 12, 1985, is an acceptable source of service information for previous accomplishment of the replacement of the MLG support beam.

We have determined that accomplishment of the actions specified in Service Bulletin 737-57A1266 will 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 Boeing Alert Service Bulletin 737-57A1266, Revision 1, except as discussed under “Differences Between the Proposed AD and Alert Service Bulletin 737-57A1266.”

Differences Between the Proposed AD and Alert Service Bulletin 737-57A1266

For airplanes identified in the service bulletin as Groups 1 through 5 on which the aft pin of the outboard stabilizing fitting has been replaced in accordance with the original issue of the service bulletin: The service bulletin recommends accomplishing the torque check of the aft pin within 36 months after the original issue date of the service bulletin, and, if the aft pin does not pass the torque check, replacing the aft pin and aft outboard stabilizing fitting within an additional 36 months after the torque check. However, we have determined that interval would not address the identified unsafe condition soon enough to ensure an adequate level of safety for the affected fleet. We find that a compliance time of within 36 months after accomplishing the replacement, or 36 months after the effective date of this AD, whichever is later, for doing the torque check and doing all applicable corrective actions before further flight, represents an appropriate interval of time for affected airplanes to continue to operate without compromising safety. This difference has been coordinated with the manufacturer.

Certain sections in Parts I, II, and V of the Accomplishment Instructions of the service bulletin specify “For 737-100 and -200 airplanes” and “For 737-300 and -500 airplanes.” Those sections are applicable to Model 737-100, -200, and -200C airplanes, and Model 737-300, -400, and -500 airplanes, respectively. Model 737-200C and -400 airplanes were inadvertently excluded from those sections.

The service bulletin also 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

There are about 3,130 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 1,380 airplanes of U.S. registry.

For all airplanes: The proposed replacement would take between 20 and 24 work hours per airplane to do, depending on the airplane's configuration, at an average labor rate of $80 per work hour. Required parts would cost between $3,658 and $4,272 per airplane, depending on the airplane's configuration. Based on these figures, the estimated cost of the proposed replacement is estimated to be up to between $7,256,040 and $8,544,960, or between $5,258 and $6,192 per airplane, depending on the airplane's configuration.

For Groups 1 through 8 airplanes: The alternative inspection, if done, would take about 12 work hours per airplane to do, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the alternative inspection is estimated to be up to $1,324,800, or $960 per airplane.

For Group 9 airplanes: The general visual inspection would take about 2 work hours per airplane to do, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the general visual inspection is estimated to be up to $220,800, or $160 per airplane.

For Groups 1 through 5 airplanes that had steel pins replaced per the original issue of the service bulletin: The torque check would take about 7 work hours per airplane to do, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the torque check is estimated to be up to $772,800, or $560 per airplane.

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 adding the following new airworthiness directive (AD):

Boeing: Docket No. FAA-2007-29062; Directorate Identifier 2007-NM-020-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by October 15, 2007.

Affected ADs

(b) None.

Applicability

(c) This AD applies to all Model 737-100, -200, -200C, -300, -400, and -500 series airplanes, certificated in any category.

Unsafe Condition

(d) This AD results from reports of findings of fatigue cracking of the outboard stabilizing fitting and stress corrosion cracking of the bolts attaching the fitting to the wing rear spar. We are issuing this AD to detect and correct that cracking, which could result in disconnection of the main landing gear (MLG) actuator from the rear spar and support beam, and consequent damage to the hydraulic system causing hydraulic fluid leakage and loss of control 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.

Service Bulletin Reference

(f) The term “alert service bulletin” as used in this AD, means the Accomplishment Instructions of Boeing Alert Service Bulletin 737-57A1266, Revision 1, dated January 3, 2007.

Replacement/Repetitive Inspections

(g) For airplanes identified as Groups 1 through 8, as specified in the alert service bulletin, except as provided by paragraphs (h) and (k) of this AD: Within 36 months after the effective date of this AD, replace the outboard stabilizing fitting, H-11 bolts, forward pin, and aft pin, as applicable, with new components by doing all the applicable actions in accordance with Part II of the alert service bulletin, except as provided by paragraph (j) of this AD. Within 120 months after accomplishing the replacement, do a general visual inspection for discrepancies of the outboard stabilizing fitting, walking beam hanger, and rear spar attachment fitting, and do all applicable corrective actions, by doing all the actions, except as provided by paragraph (j) of this AD, in accordance with Part V of the alert service bulletin. Do all corrective actions before further flight. Repeat the inspection at intervals not to exceed 120 months.

Alternative Inspection

(h) For airplanes identified as Groups 1 through 8, as specified in the alert service bulletin, on which the existing H-11 bolts were replaced before the effective date of this AD with Inconel 718 bolts, in lieu of doing the actions required by paragraph (g) of this AD: Within 4,500 flight cycles or 36 months after the effective date of this AD, whichever is later, do a magnetic test of the attach bolts in accordance with the alert service bulletin. If any bolt is magnetic, discontinue the alternative inspection specified in the alert service bulletin and accomplish the actions required by paragraph (g) before further flight. If none of the bolts are magnetic, do all the applicable actions in accordance with Part I of the alert service bulletin before further flight.

(1) If any crack is found: Stop the inspection and before further flight do the actions required by paragraph (g) of this AD. Repetitive inspections must be done after replacing the fitting at the interval specified in paragraph (g) of this AD.

(2) If no crack is found: Before further flight, replace the forward pin and aft pin, as applicable, in accordance with the alert service bulletin, and within 60 months after the effective date of this AD, do the remaining replacement required by paragraph (g) of this AD. Repetitive inspections must be done after replacing the fitting at the interval specified in paragraph (g) of this AD.

(3) If damage other than cracking is found, or if the fitting lug hole is beyond hole size limits, before further flight, repair using a method approved in accordance with the procedures specified in paragraph (p) of this AD.

General Visual Inspection

(i) For airplanes identified as Group 9, as specified in the alert service bulletin: Within 36 months or 4,500 flight cycles after the effective date of this AD, whichever occurs later, do a general visual inspection of the outboard stabilizing fitting and fasteners for discrepancies, and do all applicable corrective actions in accordance with Part IV of the alert service bulletin, except as provided by paragraphs (j) and (k) of this AD. Within 120 months after the inspection specified in Part IV has been done, do a general visual inspection for discrepancies of the outboard stabilizing fitting, walking beam hanger and rear spar attachment fitting in accordance with Part V of the alert service bulletin, and do all applicable corrective actions in accordance with Part V of the alert service bulletin, except as provided by paragraphs (j) and (k). Do all applicable corrective actions before further flight. Repeat the Part V inspection at intervals not to exceed 120 months.

Exceptions to Alert Service Bulletin Specifications

(j) During any inspection required by this AD, if any corrosion damage is found that cannot be removed, or if any damage is found that is outside the limits specified in the alert service bulletin, or if any discrepancy is found and the alert service bulletin specifies contacting the manufacturer for disposition of certain repair conditions: Before further flight, repair using a method approved in accordance with the procedures specified in paragraph (p) of this AD.

(k) Certain sections in Parts I, II, and V of the Accomplishment Instructions of the alert service bulletin specify “For 737-100 and -200 airplanes” and “For 737-300 and -500 airplanes.” However, those sections are applicable to Model 737-100, -200, and -200C airplanes, and Model 737-300, -400, and -500 airplanes, respectively.

Torque Check

(l) For airplanes identified as Groups 1 through 5, as specified in the alert service bulletin, on which the aft pin of the aft outboard stabilizing fitting was replaced before the effective date of this AD, in accordance with Boeing Alert Service Bulletin 737-57A1266, dated May 8, 2003: Within 36 months after the effective date of this AD, do a torque check to determine whether the aft pin is correctly installed. Do all applicable corrective actions before further flight. Do the actions in accordance with Part III of the alert service bulletin.

Concurrent Requirements

(m) For airplanes identified as Groups 1 and 3, as specified in the alert service bulletin: Prior to or concurrently with accomplishment of paragraph (g) of this AD, do the replacement of the existing tube assembly of the outboard stabilizing fitting as specified in Part IV of Boeing Service Bulletin 737-57-1052, Revision 4, dated October 24, 1980.

Credit for Previously Accomplished Actions

(n) Replacement of the tube assembly before the effective date of this AD in accordance with Boeing Service Bulletin 737-57-1073, Revision 4, dated April 12, 1985, is acceptable for compliance with the replacement specified in paragraph (l) of this AD.

(o) For Groups 1 through 4, as specified in the alert service bulletin: Replacement of the H-11 bolts for the inboard stabilizing fitting before the effective date of this AD, in accordance with Boeing Service Bulletin 737-57-1231 dated December 1, 1994, is acceptable for compliance with the replacement specified in paragraph (g) of this AD.

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) 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 and the approval must specifically refer to this AD.

Issued in Renton, Washington, on August 17, 2007.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.