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###### Department of Transportation

###### Federal Aviation Administration 

          - 14 CFR Part 39 
          - [Docket No. 2000-NM-350-AD] 
          - RIN 2120-AA64 

# AGENCY:

Federal Aviation Administration, DOT. 

# ACTION:

Notice of proposed rulemaking (NPRM). 

# SUMMARY:

This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747 series airplanes. This proposal would require an inspection of the flap drive transmission of the trailing edge flaps at positions 2 and 7 to determine if a wound-spring torque brake is installed, and corrective action, if necessary. This action is necessary to prevent damage to the flap system, adjacent systems, or structural components; or excessive skew of the trailing edge flap, which could result in flap asymmetry and consequent reduced controllability of the airplane. This action is intended to address the identified unsafe condition. 

# DATES:

Comments must be received by June 28, 2001. 

# ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-350-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal holidays. Comments may be submitted via fax to (425) 227-1232. Comments may also be sent via the Internet using the following address: 9-anm-nprmcomment@faa.gov. Comments sent via fax or the Internet must contain “Docket No. 2000-NM-350-AD” in the subject line and need not be submitted in triplicate. Comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 for Windows or ASCII text. 

The service information referenced in the proposed rule may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington. 

# FOR FURTHER INFORMATION CONTACT:

Barbara Mudrovich, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2983; fax (425) 227-1181. 

# SUPPLEMENTARY INFORMATION: 

## Comments Invited 

Interested persons are invited to participate in the making of the proposed rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified above. All communications received on or before the closing date for comments, specified above, will be considered before taking action on the proposed rule. The proposals contained in this action may be changed in light of the comments received. 

Submit comments using the following format: 
    - Organize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues.
    - For each issue, state what specific change to the proposed AD is being requested.
    - Include justification (e.g., reasons or data) for each request.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the proposed rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report summarizing each FAA-public contact concerned with the substance of this proposal will be filed in the Rules Docket. 

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this action must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2000-NM-350-AD.” The postcard will be date stamped and returned to the commenter. 

## Availability of NPRMs 

Any person may obtain a copy of this NPRM by submitting a request to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-350-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. 

## Discussion 

The FAA has received a report that, during overhaul of certain torque brakes of the trailing edge flap transmissions on certain Boeing Model 747 series airplanes, the brakes did not lock out at the intended torque levels. This has been attributed to the actual lock-out torque being higher than the design levels. If the torque brake fails to limit torque out of the transmission during a flap jam condition, the resulting force could cause the transmission mounts to fail. Such failure of a transmission mount on a transmission with a no-back brake could push the flap into the wing, which could result in a full flap asymmetry. These conditions could cause damage to the flap system, adjacent systems, or structural components; or excessive skew of the trailing edge flap, and which could result in flap asymmetry and consequent reduced controllability of the airplane. 

## Explanation of Relevant Service Information 

The FAA has reviewed and approved Boeing Service Bulletin 747-27-2374, dated November 18, 1999, which describes procedures for inspection of certain flap drive transmissions of the trailing edge flaps at positions 2 and 7 to determine if a wound-spring torque brake is installed, and corrective action, if necessary. The corrective action includes, but is not limited to, replacement of the flap drive transmission with a new, improved transmission; and rework or replacement of the torque brake assembly with a new, improved assembly, if a wound-spring torque brake is installed. 

The service bulletin references MOOG Service Bulletin 544666-27-16, dated November 1, 1999, as the source of service information for accomplishment of rework of the torque brake. Accomplishment of the actions specified in the service bulletin is intended to adequately address the identified unsafe condition. 

## Explanation of Requirements of Proposed Rule 

Since an unsafe condition has been identified that is likely to exist or develop on other products of this same type design, the proposed AD would require accomplishment of the actions specified in the service bulletin described previously, except as discussed below. 

## Differences Between This Proposed AD and the Service Bulletin 

                    Although the service bulletin recommends doing the inspection at the earliest convenient maintenance opportunity, the FAA has determined that this compliance time may not                           ( print page 24305)                        ensure that the identified unsafe condition is addressed in a timely manner. In developing an appropriate compliance time for this proposed AD, the FAA considered not only the manufacturer's recommendation, but the degree of urgency associated with addressing the subject unsafe condition, the average utilization of the affected fleet, and the time necessary to perform the proposed AD. In light of all of these factors, the FAA finds a compliance time of 6,000 flight hours after the effective date of this AD to be warranted, in that it represents an appropriate interval of time allowable for affected airplanes to continue to operate without compromising safety.                 

The service bulletin also recommends replacement of the flap drive transmission and/or torque brake of the trailing edge flap transmission at positions 2, 4, 5, and 7. The FAA has determined that an unsafe condition exists at positions 2 and 7 only. This determination was made from a probability assessment indicating that positions 4 and 5 do not warrant mandatory action because the likelihood of failure of a torque brake to limit torque out of the transmission during a flap jam condition at these positions is extremely remote. Additionally, full flap asymmetry is not likely to occur at positions 4 and 5. Therefore, this proposed AD is applicable to positions 2 and 7 only. 

## Cost Impact 

There are approximately 1,181 airplanes of the affected design in the worldwide fleet. The FAA estimates that 263 airplanes of U.S. registry would be affected by this proposed AD. 

It would take approximately 1 work hour per airplane to accomplish the inspection, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the inspection proposed by this AD on U.S. operators is estimated to be $15,780, or $60 per airplane. 

The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this proposed AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. 

## Regulatory Impact 

The regulations proposed herein 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. Therefore, it is determined that this proposal would not have federalism implications under Executive Order 13132. 

                    For the reasons discussed above, I certify that this 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) if promulgated, 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. A copy of the draft regulatory evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting the Rules Docket at the location provided under the caption                     **ADDRESSES.**

# List of Subjects in 14 CFR Part 39

      - Air transportation
      - Aircraft
      - Aviation safety
      - Safety

## The Proposed Amendment 

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend part 39 of the Federal Aviation Regulations (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 

2. Section 39.13 is amended by adding the following new airworthiness directive:

**Boeing:**                                 Docket 2000-NM-350-AD.                            

*Applicability:*                                 Model 747 series airplanes, as listed in Boeing Service Bulletin 747-27-2374, dated November 18, 1999; certificated in any category.                             

# Note 1:

This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (c) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

*Compliance:*                                 Required as indicated, unless accomplished previously.                             

To prevent damage to the flap system, adjacent systems, or structural components; or excessive skew of the trailing edge flap; which could result in flap asymmetry and consequent reduced controllability of the airplane, accomplish the following: 

## Part Verification/Replacement/Modification 

(a) Within 6,000 flight hours after the effective date of this AD: Inspect the flap drive transmission of the trailing edge flaps at positions 2 and 7 to determine if a wound-spring torque brake is installed in the transmission, by verifying the transmission part number, per Boeing Service Bulletin 747-27-2374, dated November 18, 1999. Then do the actions specified in paragraphs (a)(1), (a)(2), (a)(3), and (a)(4) of this AD, as applicable. 

(1) If the part number of the flap drive transmission shows that no wound-spring torque brake is installed, no further action is required by this AD. 

(2) If the part number of the flap drive transmission shows that a wound-spring torque brake may be installed, before further flight, inspect the part number of the torque brake to verify whether it is a wound-spring torque brake, per the Accomplishment Instructions of the service bulletin. 

(i) If the part number of the torque brake shows that it is not a wound-spring torque brake, no further action is required by this AD. 

(ii) If the part number of the torque brake shows that it is a wound-spring torque brake, before further flight, rework the torque brake or replace the torque brake with a new, improved brake, as applicable; per the Accomplishment Instructions of the service bulletin. 

## Spares 

(b) As of the effective date of this AD, no person shall install on any airplane any transmission or torque brake assembly identified in the “Existing Part Number” column of Paragraph 2.E. of Boeing Service Bulletin 747-27-2374, dated November 18, 1999. 

## Alternative Methods of Compliance 

(c) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO. 

# Note 2:

Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

## Special Flight Permit 

                                (d) Special flight permits may be issued in accordance with sections 21.197 and 21.199                                       ( print page 24306)                                    of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.                            

Issued in Renton, Washington, on May 8, 2001. 

Donald L. Riggin, 

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service. 

[FR Doc. 01-12008 Filed 5-11-01; 8:45 am] 

BILLING CODE 4910-13-U