E6-1767. Airworthiness Directives; Boeing Model 777-200 and 777-300 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 certain Boeing Model 777-200 and 777-300 series airplanes. This proposed AD would require repetitive inspections for discrepancies of the splined components that support the inboard end of the inboard trailing edge flap, and related investigative, corrective, and other specified actions if necessary. This proposed AD would also require a one-time modification of the inboard support of the inboard trailing edge flap by installing a new isolation strap and attachment hardware. This proposed AD would also require repetitive replacement of the torque tube assembly. This proposed AD results from reports of corrosion on the torque tube and closeout rib fittings that support the inboard end of the inboard trailing edge flap, as well as a structural reassessment of the torque tube joint that revealed the potential for premature fatigue cracking of the torque tube that would not be detected using reasonable inspection methods. We are proposing this AD to detect and correct corrosion or cracking of the torque tube and closeout rib fittings that support the inboard end of the inboard trailing edge flap. Cracking in these components could lead to a fracture, which could result in loss of the inboard trailing edge flap and consequent reduced controllability of the airplane.

DATES:

We must receive comments on this proposed AD by March 27, 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 the service information identified in this proposed AD.

FOR FURTHER INFORMATION CONTACT:

Gary Oltman, 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-2006-23842; Directorate Identifier 2005-NM-145-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 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

We have received reports that corrosion has been found on the torque tube and closeout rib fitting assembly that support the inboard end of the inboard trailing edge flap on certain Boeing Model 777-200 and -300 series airplanes. Investigation has revealed contact between the splined areas of the torque tube and closeout rib fitting, causing wear to the titanium-cadmium plating of the components. When the grease on these components dries out, moisture may enter the area, and corrosion may form in areas where the plating has worn away. This corrosion may subsequently lead to corrosion pitting and cracking that can propagate by stress corrosion. Also, a structural reassessment of Boeing Model 777-200 and 777-300 series airplanes revealed the potential for premature fatigue cracking of the torque tube of the inboard trailing edge flap, whether or not the torque tube is corroded. This premature fatigue cracking would not be detected by traditional inspection methods such as visual or non-destructive inspection techniques. Cracking of the torque tube or closeout rib fitting, if not corrected, could lead to a fracture of the torque tube or a closeout rib fitting, which could result in loss of the inboard trailing edge flap and consequent reduced controllability of the airplane.

Relevant Service Information

We have reviewed Boeing Service Bulletin 777-57A0048, Revision 1, dated June 9, 2005. The service bulletin describes procedures for performing repetitive detailed inspections for any discrepancy of the splined components (torque tube, closeout rib fitting, carrier beam pillow block fitting assembly (i.e., the matched set of two carrier beam pillow block fittings) and the drive crank support) that support the inboard end of the inboard trailing edge flap. Discrepancies of the torque tube and closeout rib fitting include light contact wear, corrosion pits, corrosion, cracking, and fracture. Discrepancies of the other splined components consist of damage to the cadmium plating. (The carrier beam pillow block fitting assembly and drive crank support are made from corrosion-resistant steel. The condition of the plating on these components must be inspected because the plating helps to protect these components from the steel torque tube, which is made of less corrosion-resistant 4330M steel.)

If no discrepancy is found, the service bulletin describes procedures for other specified actions that include:

• Assembling the splined components with corrosion-inhibiting compound.
• Modifying certain splined components by installing a new isolation strap and attachment hardware. (Installing the isolation strap is intended to prevent a washer installed between the drive crank support and the carrier beam pillow block fittings from coming into contact with the torque tube splines, which could damage the finish on the torque tube splines.)
• Refinishing the components as necessary.

If a discrepancy is found, the service bulletin describes procedures for corrective actions that include:

• Determining the condition of the spline interface by doing an evaluation of the level of spline rework using the guidelines in Appendix A of the service bulletin.
• Blending out light contact wear (defined in the service bulletin as shallow surface irregularities or discrete pits, which can be blended out using unpowered hand tools).
• Reworking corroded or corrosion-pitted components according to the Spline Rework procedures in Part 3 of the service bulletin if the damage is within specified limits.
• Replacing corroded or corrosion-pitted components having damage that is outside the specified limits with new or serviceable components.
• Replacing cracked or fractured components with new or serviceable components. (The service bulletin notes that, if one of the two fittings that make up the closeout rib fitting assembly or the carrier beam pillow block fitting assembly is replaced, both fittings that make up the assembly must be replaced at the same time.)
• Refinishing components as necessary.

If spline rework is accomplished, the service bulletin also describes procedures for performing additional investigative actions that include:

• Evaluating the interfaces between the splined components using the Spline Rework Evaluation or the Preliminary Spline Rework Evaluation procedure, as applicable.
• Doing a magnetic particle inspection of the splined area for cracking.
• Doing a detailed inspection for corrosion or corrosion pitting to ensure complete removal of corrosion or corrosion pitting.
• Doing a detailed inspection for discoloration due to overheating, or a local surface temper etch inspection for other damage, that may have resulted from performing the rework procedures.

The service bulletin specifies a compliance time for the initial inspection of 48 months after the date of issuance of the original Airworthiness Certificate or the date of issuance of the original Export Certificate of Airworthiness, or within 24 months after the date of Revision 1 of the service bulletin, whichever is later. The service bulletin specifies repeating the detailed inspections for any discrepancy of the splined components that support the inboard end of the inboard trailing edge flap within 5 years or 10 years, depending on the condition of the splined components. (Subsequent inspections are required at intervals not to exceed 5 years or 10 years, depending on the condition found during the repeat inspection.) If the criteria for Condition D are met during the initial inspection (as determined by the spline evaluation), a repeat inspection is required within 24 months. If the criteria for Condition C or D are met in a subsequent repeat inspection, the affected splined component must be replaced before further flight.

Note (c) of Table 7, under paragraph 1.E., “Compliance,” of the service bulletin also specifies repetitively replacing the torque tube assembly with a new torque tube assembly, regardless of condition. The service bulletin specifies an initial compliance time for this replacement of either 18,000 or 20,000 total flight cycles on the airplane (depending on airplane group), or 24 months after the date of Revision 1 of the service bulletin, whichever is later. The repetitive interval for the replacement is either 18,000 or 20,000 flight cycles, depending on airplane group.

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 below under “Difference Between Proposed AD and Service Information.”

Difference Between Proposed AD and Service Information

The service bulletin specifies compliance times relative to the date of issuance of the service bulletin; however, this proposed AD would require compliance before the specified compliance time after the effective date of this AD.

Clarification of Requirement To Replace Torque Tube Assembly

As explained previously, Note (c) of Table 7, under paragraph 1.E., “Compliance,” of the service bulletin specifies repetitively replacing the torque tube assembly with a new torque tube assembly, regardless of condition. However, this replacement of a torque tube assembly with no discrepancy is not specified in the Accomplishment Instructions of the service bulletin. Paragraph (k) of this proposed AD would require the repetitive replacement of the torque tube assembly at the schedule indicated in the Compliance section of the service bulletin.

Interim Action

We consider this proposed AD interim action. The manufacturer is currently developing a new, improved torque tube that will be made from corrosion-resistant steel and have thicker walls. Installing this new, improved torque tube is expected to address the unsafe condition identified in this proposed AD and eliminate the need for the repetitive inspections and torque tube assembly replacements that would be required by this proposed AD. Once the improved torque tube is developed, approved, and available, we may consider additional rulemaking to require installing it.

Costs of Compliance

There are about 353 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, at an average labor rate of $65 per work hour.

Estimated Costs

Action	Work hours	Parts	Cost per airplane	Number of U.S.-registered airplanes	Fleet cost
Detailed inspection for discrepancies of the splined components	20	None	$1,300, per inspection cycle	132	$171,600, per inspection cycle.
Modification (Installing isolation strap and hardware)	Negligible	$17,156	$17,156	132	$2,264,592.
Replacement of torque tube assembly	Negligible 1	$24,230	$24,230	132	$3,198,360, per replacement cycle.
1 Provided that the replacement is performed at the same time as a scheduled inspection.

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-2006-23842; Directorate Identifier 2005-NM-145-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by March 27, 2006.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Boeing Model 777-200 and -300 series airplanes, certificated in any category, as identified in Boeing Service Bulletin 777-57A0048, Revision 1, dated June 9, 2005.

Unsafe Condition

(d) This AD results from reports of corrosion on the torque tube and closeout rib fittings that support the inboard end of the inboard trailing edge flap, as well as a structural reassessment of the torque tube joint that revealed the potential for premature fatigue cracking of the torque tube that would not be detected using reasonable inspection methods. We are issuing this AD to detect and correct corrosion or cracking of the torque tube and closeout rib fittings that support the inboard end of the inboard trailing edge flap. Cracking in these components could lead to a fracture, which could result in loss of the inboard trailing edge flap and consequent 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.

Service Bulletin Reference

(f) The term “service bulletin,” as used in this AD, means Boeing Service Bulletin 777-57A0048, Revision 1, dated June 9, 2005.

(g) Where the service bulletin specifies a compliance time after the issuance of the service bulletin, this AD requires compliance within the specified compliance time after the effective date of this AD.

Initial Inspection

(h) Do a detailed inspection for any discrepancy of the splined components of the inboard trailing edge flap, in accordance with the Accomplishment Instructions of the service bulletin. The splined components of the inboard trailing edge flap include the torque tube, closeout rib fitting assembly, carrier beam pillow block fitting assembly, and drive crank support. Discrepancies of the torque tube and closeout rib fitting include light contact wear, corrosion pits, corrosion, cracking, or fracture. Discrepancies of the carrier beam pillow block fitting assembly and drive crank support consist of light contact wear and damage to the cadmium plating. Do the initial inspection at the applicable time specified in Table 7 under paragraph 1.E., “Compliance,” of the service bulletin, except as provided by paragraph (g) of this AD.

No Discrepancy/Other Specified Actions

(i) If no discrepancy is found, perform all applicable specified actions, including the modification to install a new isolation strap and attachment hardware, in accordance with the Accomplishment Instructions of the service bulletin. Then, repeat the inspection at the applicable time specified in Table 7 under paragraph 1.E., “Compliance,” of the service bulletin.

Related Investigative/Corrective/Other Specified Actions and Repetitive Inspections

(j) For any discrepancy found during any inspection required by this AD: Before further flight, accomplish all applicable investigative, corrective, and other specified actions, including the modification to install a new isolation strap and attachment hardware, in accordance with the Accomplishment Instructions of the service bulletin. Then, evaluate the spline rework to determine the appropriate repetitive interval, in accordance with the Accomplishment Instructions of the service bulletin. Thereafter, repeat the inspection at the applicable interval specified in Table 7 under paragraph 1.E., “Compliance,” of the service bulletin.

Replacement of Torque Tube Assembly

(k) Replace the torque tube assembly with a new torque tube assembly, in accordance with the Accomplishment Instructions of the service bulletin. Do the initial replacement at the applicable compliance time specified in Notes (c) and (d), as applicable, of Table 7 in paragraph 1.E., “Compliance,” of the service bulletin, except as provided by paragraph (g) of this AD. Repeat the replacement thereafter at the applicable interval specified in Notes (c) and (d), as applicable, of Table 7 under paragraph 1.E., “Compliance,” of the service bulletin.

Alternative Methods of Compliance (AMOCs)

(l)(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.

Issued in Renton, Washington, on January 31, 2006.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.