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Airworthiness Directives; Learjet Model 45 Airplanes

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Information about this document as published in the Federal Register.

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Federal Aviation Administration, DOT.


Final rule; request for comments.


This amendment adopts a new airworthiness directive (AD) that is applicable to all Learjet Model 45 airplanes. This action requires replacement of the horizontal stabilizer actuator assembly (HSAA) with a new HSAA. This action is necessary to prevent structural failure of the HSAA, which could result in possible loss of control of the airplane. This action is intended to address the identified unsafe condition.


Effective August 13, 2003.

Comments for inclusion in the Rules Docket must be received on or before October 14, 2003.


Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2003-NM-142-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9 a.m. and 3 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: Comments sent via fax or the Internet must contain “Docket No. 2003-NM-142-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 or 2000 or ASCII text.

Information pertaining to this amendment may be examined at the FAA, Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Wichita Aircraft Certification Office, 1801 Airport Road, Room 100, Mid-Continent Airport, Wichita, Kansas.

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Greg Davied, Aerospace Engineer, Airframe and Propulsion Branch, ACE-118W, FAA, Wichita Aircraft Certification Office, 1801 Airport Road, Room 100, Mid-Continent Airport, Wichita, Kansas 67209; telephone (316) 946-4128; fax (316) 946-4107.

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On April 11, 2003, the FAA issued AD 2003-06-51, amendment 39-13121 (68 FR 19328, April 21, 2003), applicable to certain Learjet Model 45 airplanes, to require an inspection to determine the part number (P/N) of the horizontal stabilizer actuator assembly (A66) (HSAA), and replacement of any suspect HSAA (A66) having P/N 6627401000-001 or SA9200F with a new or serviceable HSAA (A66) having P/N 6627401000-005. That action was prompted by a report of severe vibration followed by a rapid nose down pitch change on a Learjet Model 45 airplane. The cause of the incident is attributed to brittle fracture material properties of certain components of the HSAA. The requirements of that AD are intended to prevent structural failure of the HSAA, which could result in possible loss of control of the airplane.

FAA's Determination Since Issuance of AD 2003-06-51

Since issuance of AD 2003-06-51, we have determined that the MPC Products Corporation acme screw having P/N 2A94568008 and nut having P/N 2A94567005 within the new HSAA having P/N 6627401000-005 installed per that AD are physically similar (not identical) to and have the same material as the suspect assembly having P/N 6627401000-001. Although the HSAA having P/N-005 is an improvement over the P/N-001, it was not manufactured per the type design data. A brittle fracture could occur on the acme screw and nut within the assembly having P/N-005, similar to that on the assembly having P/N-001. During our investigation of this problem, we determined that the configuration and quality controls over the production of these parts were so deficient that we do not have confidence that the airplane can be operated safely for any period of time. Therefore, this AD allows operation only for the purpose of positioning the airplane where the replacement required by this AD can be accomplished. The airplane manufacturer is currently substantiating the design data for the new replacement part. We anticipate that the new part will be available in the near future.

Explanation of the Requirements of the Rule

Since an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same Start Printed Page 48275type design registered in the United States, this AD requires replacement of the HSAA with a new HSAA. The effect of this AD is that operation is prohibited after the effective date of this AD, except to position the airplane as described previously, until the required replacement can be accomplished.

Interim Action

This is considered to be interim action until final action is identified, at which time the FAA may consider further rulemaking.

Changes to 14 CFR Part 39/Effect on the AD

On July 10, 2002, we issued a new version of 14 CFR part 39 (67 FR 47997, July 22, 2002), which governs our AD system. The regulation now includes material that relates to altered products, special flight permits, and alternative methods of compliance (AMOCs). Because we have now included this material in part 39, only the office authorized to approve AMOCs is identified in each individual AD.

Determination of Rule's Effective Date

Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.

Comments Invited

Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this 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 under the caption ADDRESSES. All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.

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 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 rule that might suggest a need to modify the 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 that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2003-NM-142-AD.” The postcard will be date stamped and returned to the commenter.

Regulatory Impact

The regulations adopted herein will 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 final rule does not have federalism implications under Executive Order 13132.

The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a “significant regulatory action” under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption ADDRESSES.

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List of Subjects in 14 CFR Part 39

  • Air transportation
  • Aircraft
  • Aviation safety
  • Safety
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Adoption of the Amendment

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Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:

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1. The authority citation for part 39 continues to read as follows:

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Authority: 49 U.S.C. 106(g), 40113, 44701.

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

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2003-16-19 Learjet: Amendment 39-13272. Docket 2003-NM-142-AD.

Applicability: All Model 45 airplanes, certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To prevent structural failure of the horizontal stabilizer actuator assembly (HSAA), which could result in possible loss of control of the airplane, accomplish the following:


(a) Except as provided by paragraph (b) of this AD, before further flight after the effective date of this AD, replace the HSAA having part number (P/N) 6627401000-005 with a new HSAA, per a method approved by the Manager, Wichita Aircraft Certification Office (ACO), FAA.

Flight Limits

(b) Non-revenue flights are permitted within 3 days after the effective date of this AD only for the purpose of positioning the airplane to a location where the replacement required by paragraph (a) of this AD can be accomplished.

Parts Installation

(c) As of the effective date of this AD, no person may install an HSAA, P/N 6627401000-005, on any airplane.

Alternative Methods of Compliance

(d) In accordance with 14 CFR 39.19, the Manager, Wichita Aircraft Certification Office (ACO), FAA, is authorized to approve alternative methods of compliance for this AD.

Effective Date

(e) This amendment becomes effective August 13, 2003.

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Issued in Renton, Washington, on August 8, 2003.

Vi L. Lipski,

Manager, Transport Airplane Directorate, Aircraft Certification Service.

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[FR Doc. 03-20699 Filed 8-12-03; 8:45 am]