E7-23955. Airworthiness Directives; Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747-400D, 747-400F, and 747SR 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 747 airplanes identified above. This proposed AD would require modifying the outboard flap track and transmission attachments. This proposed AD results from a joint Boeing and FAA multi-model study (following in-service trailing edge flap structure and drive system events) on the hazards posed by skewing and failed flaps. This study identified the safety concerns regarding the transmission attachment design and the potential loss of an outboard trailing edge flap. We are proposing this AD to prevent certain discrepancies associated with this design (for example, a flap skew or lateral control asymmetry that can cause collateral damage to adjacent hydraulic tubing and subsequent loss of a hydraulic system), which could result in the asymmetric flight control limits being exceeded, and could adversely affect the airplane's continued safe flight and landing.

DATES:

We must receive comments on this proposed AD by January 25, 2008.

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 proposed 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:

Doug Tsuji, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, 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-2007-0308; Directorate Identifier 2007-NM-160-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

A report has been completed about a joint Boeing and FAA multi-model study (following in-service trailing edge flap structure and drive system events) on the hazards posed by skewing and failed flaps. The study identified safety concerns with the transmission attachment design, which does not meet the single failure condition analysis criteria. Three bolts attach the transmission to the flap track. The fracture of one of the transmission attachment bolts in flight could lead to an overload failure of the two remaining bolts and subsequent loss of the transmission. In addition, a support housing with an undetected fracture could lead to the loss of the transmission. Loss of the flap transmission could lead to a flap skew or lateral control asymmetry. Loss of a transmission could lead to possible collateral damage to adjacent hydraulic tubing and the loss of a hydraulic system. A flap skew or asymmetry combined with collateral hydraulic system damage could result in the asymmetric flight control limits being exceeded, and could adversely affect the airplane's continued safe flight and landing.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletins 747-27A2398 and 747-27A2421, both dated April 19, 2007. The service bulletins describe the following procedures for modifying the outboard trailing edge flaps, including the following “airplane work”:

• Replacing the flap tracks and flap transmissions with a new configuration (flap tracks and flap transmissions 1, 2, 7, and 8);
• Reversing the bolt direction on the flap track side load fitting; and
• Installing new flap track fairing hinge braces. The service bulletins describe the following component work:
• Replacing the upper forward and the upper aft flap transmission attachment bolt hole bushings;
• Replacing the support housing;
• Machining the track and installing the larger diameter bolt hole bushings, at the upper forward and upper aft flap transmission attachment locations (flap track assemblies 1 and 8) and at the upper aft flap transmission attachment location (flap track assemblies 2 and 7); and
• Replacing the existing support housing with the new support housing (flap transmission assemblies 1, 2, 7, and 8).

The compliance time is 6 years for airplanes known to have fewer than 20,000 total flight cycles, and 3 years for all other airplanes.

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 the actions specified in the service information described previously.

Costs of Compliance

There are about 990 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

Work hours	Average labor rate per hour	Parts	Cost per airplane	Number of U.S.-registered airplanes	Fleet cost
150	$80	$80,023	$92,023	141	$12,975,243

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-2007-0308; Directorate Identifier 2007-NM-160-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by January 25, 2008.

Affected ADs

(b) None.

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, 747-400D, 747-400F, and 747SR series airplanes, certificated in any category; as identified in Boeing Alert Service Bulletin 747-27A2398 or 747-27A2421, both dated April 19, 2007.

Unsafe Condition

(d) This AD results from a joint Boeing and FAA multi-model study (following in-service trailing edge flap structure and drive system events) on the hazards posed by skewing and failed flaps. This study identified the safety concerns regarding the transmission attachment design and the potential loss of an outboard trailing edge flap. We are issuing this AD to prevent certain discrepancies associated with this design (for example, a flap skew or lateral control asymmetry that can cause collateral damage to adjacent hydraulic tubing and subsequent loss of a hydraulic system), which could result in the asymmetric flight control limits being exceeded, and could adversely affect the airplane's continued safe flight and landing.

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.

Modification

(f) Do the following, as applicable: At the time specified in paragraph 1.E. of Boeing Alert Service Bulletin 747-27A2421 or 747-27A2398, both dated April 19, 2007, except as provided by paragraph (g) of this AD, modify the outboard flap track and transmission attachments by doing all actions specified in the Accomplishment Instructions of the service bulletin.

(g) Where Boeing Alert Service Bulletins 747-27A2421 and 747-27A2398, both dated April 19, 2007, specify compliance times relative to the date on the service bulletin, this AD requires compliance within the specified compliance time after the effective date of this AD.

Parts Installation

(h) As of the effective date of this AD, no person may install a part identified in Table 1 of this AD on any airplane.

Table 1.—Parts Prohibited From Installation

Part	Part No.
Hinge brace for Tracks 1 and 8	65B15515-1 65B15515-2
	65B15515-9
	65B15515-10
Hinge brace for Tracks 2 and 7	65B15525-1 65B15525-2
	65B15525-7
	65B15525-8
	65B17092-1
	65B17092-2
Support assembly for Tracks 1 and 8	65B81982-( )
Support assembly for Tracks 2 and 7	65B81950-( )

Alternative Methods of Compliance (AMOCs)

(i)(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.

Issued in Renton, Washington, on November 13, 2007.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.