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###### Department of Transportation

###### Federal Aviation Administration 

          - 14 CFR Part 39 
          - [Docket No. FAA-2005-22169; Directorate Identifier 2005-NM-094-AD; Amendment 39-14361; AD 2005-23-03] 
          - RIN 2120-AA64 

# AGENCY:

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

# ACTION:

Final rule. 

# SUMMARY:

The FAA is adopting a new airworthiness directive (AD) for certain Learjet Model 23, 24, 24A, 24B, 24B-A, 24C, 24D, 24D-A, 24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, and 25F airplanes. This AD requires replacement of the spherical accumulator for the main hydraulic system with a new cylindrical accumulator. For certain airplanes, this AD also requires modification of the accumulator pressure gauge. This AD results from reports of the failure of two thrust reverser accumulators (which are similar to the main hydraulic system's spherical accumulator) and fatigue cracks found on four thrust reverser accumulators. We are issuing this AD to prevent failure of the spherical accumulator for the main hydraulic system, due to fatigue cracking on the threads, which could result in the loss of hydraulic power, damage to the surrounding airplane structure, and loss of airplane control. The failure of the accumulator could also result in injury to any persons in the surrounding area. The loss of hydraulic fluid could also leak onto a potential source of ignition and result in a consequent fire. 

# DATES:

This AD becomes effective December 19, 2005. 

The Director of the Federal Register approved the incorporation by reference of certain publications listed in the AD as of December 19, 2005. 

# ADDRESSES:

                        You may examine the AD docket on the Internet at                         *http://dms.dot.gov*                         or in person at the Docket Management Facility, U.S. Department of Transportation, 400 Seventh Street SW., Nassif Building, room PL-401, Washington, DC.                     

Contact Learjet, Inc., One Learjet Way, Wichita, Kansas 67209-2942, for service information identified in this AD. 

# FOR FURTHER INFORMATION CONTACT:

Robert Busto, Aerospace Engineer, Systems and Propulsion Branch, ACE-116W, FAA, Wichita Aircraft Certification Office, 1801 Airport Road, Room 100, Mid-Continent Airport, Wichita, Kansas 67209; telephone (316) 946-4157; fax (316) 946-4107. 

# SUPPLEMENTARY INFORMATION: 

## Examining the Docket 

                    You may examine the airworthiness directive (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 (800) 647-5227) is located on the plaza level of the Nassif Building at the street address stated in the                     **ADDRESSES**                     section.                 

## Discussion 

                    The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to include an AD that would apply to certain Learjet Model 23, 24, 24A, 24B, 24B-A, 24C, 24D, 24D-A, 24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, and 25F airplanes. That NPRM was published in the                     **Federal Register**                     on August 23, 2005 (70 FR 49210). That NPRM proposed to require replacement of the spherical accumulator for the main hydraulic system with a new cylindrical accumulator. For certain                           ( print page 69070)                        airplanes, that proposed AD would also require modification of the accumulator pressure gauge.                 

## Comments 

We provided the public the opportunity to participate in the development of this AD. We received no comments on the NPRM or on the determination of the cost to the public. 

## Clarification of Alternative Method of Compliance (AMOC) Paragraph 

We have revised this action to clarify the appropriate procedure for notifying the principal inspector before using any approved AMOC on any airplane to which the AMOC applies. 

## Conclusion 

We have carefully reviewed the available data, and determined that air safety and the public interest require adopting the AD with the change described previously. We have determined that this change will neither increase the economic burden on any operator nor increase the scope of the AD. 

## Costs of Compliance 

There are about 434 airplanes of the affected design in the worldwide fleet. This AD will affect about 242 airplanes of U.S. registry. The actions will take about 9 to 13 work hours per airplane, at an average labor rate of $65 per work hour. Required parts will cost about $1,336 to $1,363 per airplane. Based on these figures, the estimated cost of the AD for U.S. operators is $464,882 to $534,336, or $1,921 to $2,208 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 AD will not have federalism implications under Executive Order 13132. This AD 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. 

For the reasons discussed above, I certify that this AD: 

(1) Is not a “significant regulatory action” under Executive Order 12866; 

(2) Is not a “significant rule” under 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 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
      - Incorporation by reference
      - Safety

## Adoption of the Amendment 

Accordingly, under the authority delegated to me by the Administrator, the FAA amends 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. The Federal Aviation Administration (FAA) amends § 39.13 by adding the following new airworthiness directive (AD): 

**2005-23-03 Learjet:**                             Amendment 39-14361. Docket No. FAA-2005-22169; Directorate Identifier 2005-NM-094-AD.                         

## Effective Date 

(a) This AD becomes effective December 19, 2005. 

## Affected ADs 

(b) None. 

## Applicability 

(c) This AD applies to Learjet Model 23, 24, 24A, 24B, 24B-A, 24C, 24D, 24D-A, 24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, and 25F airplanes, certificated in any category; having serial numbers 23-003 through 23-099 inclusive, 24-100 through 24-284 inclusive, and 25-003 through 25-153 inclusive. 

## Unsafe Condition 

(d) This AD results from reports of the failure of two thrust reverser accumulators (which are similar to the main hydraulic system's accumulator) and fatigue cracks found on four thrust reverser accumulators. We are issuing this AD to prevent failure of the spherical accumulator for the main hydraulic system, due to fatigue cracking on the threads, which could result in the loss of hydraulic power, damage to the surrounding airplane structure, and loss of airplane control. The failure of the accumulator could also result in injury to any persons in the surrounding area. The loss of hydraulic fluid could also leak onto a potential source of ignition and result in a consequent fire. 

## 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. 

## Replacement 

(f) Within 60 days after the effective date of this AD, replace the spherical accumulator having part number (P/N) 2380025-() or P/N 2380167-() with a new cylindrical accumulator having P/N 2497202-801, in accordance with the Accomplishment Instructions of Bombardier Alert Service Bulletin A23/24/25-29-4, Revision 1, dated January 17, 2005. 

## Concurrent Action 

(g) For airplanes having serial numbers 23-003 through 23-014 inclusive: Prior to or concurrently with the actions in Bombardier Alert Service Bulletin A23/24/25-29-4, Revision 1, dated January 17, 2005, relocate the accumulator pressure gauge in accordance with Learjet Service Kit SK23-215, dated April 4, 1966. 

## Parts Installation 

(h) As of the effective date, no spherical accumulator having P/N 2380025-() or P/N 2380167-() may be installed on any airplane. 

## Previous Actions 

(i) Replacements done before the effective date of this AD in accordance with Bombardier Alert Service Bulletin A23/24/25-29-4, dated August 20, 2004, are acceptable for compliance with the requirements of paragraph (f) of this AD. 

## No Reporting Required 

(j) Although the service bulletin referenced in this AD specifies to submit certain information to the manufacturer, this AD does not include that requirement. 

## Alternative Methods of Compliance (AMOCs) 

(k)(1) The Manager, Wichita Aircraft Certification Office, 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.                                   ( print page 69071)    

## Material Incorporated by Reference 

                            (l) You must use Bombardier Alert Service Bulletin A23/24/25-29-4, Revision 1, dated January 17, 2005; and Learjet Service Kit SK23-215, dated April 4, 1966; as applicable, to perform the actions that are required by this AD, unless the AD specifies otherwise. (The issue date of Learjet Service Kit SK23-215 is located only on the first and last pages of the document.) The Director of the Federal Register approved the incorporation by reference of this document in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Contact Learjet, Inc., One Learjet Way, Wichita, Kansas 67209-2942, for a copy of this service information. You may review copies at the Docket Management Facility, U.S. Department of Transportation, 400 Seventh Street SW., room PL-401, Nassif Building, Washington, DC; on the Internet at                             *http://dms.dot.gov*; or at the National Archives and Records Administration (NARA). For information on the availability of this material at the NARA, call (202) 741-6030, or go to                             *http://www.archives.gov/​federal_​register/​code_​of_​federal_​regulations/​ibr_​locations.html.*

Issued in Renton, Washington, on October 26, 2005. 

Kalene C. Yanamura, 

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service. 

[FR Doc. 05-22220 Filed 11-10-05; 8:45 am] 

BILLING CODE 4910-13-P