Airworthiness Directives; Learjet Model 23, 24, 24A, 24B, 24B-A, 24D, 24D-A, 24E, 24F, 25, 25A, 25B, 25C, 25D, and 25F Airplanes Modified by Supplemental Type Certificate SA1731SW, SA1669SW, or SA1670SW

Summary:

The FAA proposes to adopt a new airworthiness directive (AD) for certain Learjet Model 23, 24, 24A, 24B, 24B-A, 24D, 24D-A, 24E, 24F, 25, 25A, 25B, 25C, 25D, and 25F airplanes. This proposed AD would require removing the thrust reverser accumulator, and making the thrust reverser hydraulic system and the thrust reversers inoperable. This proposed AD is prompted by reports of the failure of two thrust reverser accumulators. We are proposing this AD to prevent failure of the thrust reverser accumulators, due to fatigue cracking on the female threads, which could result in the loss of hydraulic power and damage to the surrounding airplane structure.

Table of Contents

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.

• By fax: (202) 493-2251.

• 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.

For service information identified in this proposed AD, contact The Nordam Group, Nacelle/Thrust Reverser Systems Division, 6911 North Whirlpool Drive, Tulsa, OK 74117.

You can examine the contents of this 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., room PL-401, on the plaza level of the Nassif Building, Washington, DC. This docket number is FAA-2005-20947; the directorate identifier for this docket is 2004-NM-245-AD.

For further information contact:

Jim Rankin, Aerospace Engineer, Special Certification Office, ASW-190, FAA, Rotorcraft Directorate, 2601 Meacham Boulevard, Fort Worth, Texas, 76137-4298; telephone (817) 222-5138; fax (817) 222-5785.

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 under ADDRESSES. Include “Docket No. FAA-2005-20947; Directorate Identifier 2004-NM-245-AD” in the subject line 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 submitted 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 can review DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you can visit http://dms.dot.gov.

Examining the Docket

You can 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 (800) 647-5227) 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 DMS receives them.

Discussion

We have received reports indicating the failure of two thrust reverser accumulators, part number (P/N) 25-0570-127-7. One of the failures occurred in flight during final approach of an airplane and resulted in the loss of hydraulic power and damage to the airplane tailcone. The other failure occurred when a repair facility was proof testing an accumulator at 2,250 psig (the accumulator is rated for 1,500 psig). Inspection of both of these thrust reverser accumulators found suspected fatigue cracking on the female threads where the halves are joined. This condition, if not corrected, could result in the loss of hydraulic power and damage to the surrounding airplane structure.

The thrust reverser accumulators having P/N 25-0570-127-1, -3, -13, or -17 on certain Learjet Model 23, 24, 24A, 24B, 24B-A, 24D, 24D-A, 24E, 24F, 25, 25A, 25B, 25C, 25D, and 25F airplanes are identical to those on the affected airplanes having P/N 25-0570-127-7. Therefore, all of these models with any of these part numbers may be subject to the same unsafe condition.

Relevant Service Information

We have reviewed The Nordam Group Alert Service Bulletin A3000 78-21, dated November 25, 2002. The service bulletin describes procedures for removing the thrust reverser accumulator, and making the thrust reverser hydraulic system and the thrust reversers inoperable.

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. Therefore, we are proposing this AD, which would require accomplishing the actions specified in the service information described previously, except as discussed under “Difference Between the Proposed AD and Service Bulletin.”

Differences Between the Proposed AD and Service Bulletin

Operators should note that, although the service bulletin specifies the compliance time as “not later than 10 flight-hours from receipt of this alert service bulletin,” this proposed AD specifies a compliance time of “within 60 days after the effective date of this AD.” In developing an appropriate compliance time for this 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 actions required by the proposed AD. In light of all of these factors, the FAA finds a compliance time of 60 days for completing the required actions to be warranted, in that it represents an appropriate interval of time for affected airplanes to continue to operate without compromising safety. This difference has been coordinated with the manufacturer.

Operators should note that, although the Accomplishment Instructions of the referenced service bulletin describe procedures for submitting a comment sheet recording compliance with the service bulletin, this proposed AD would not require that action. We do not need this information from operators.

Interim Action

This is considered to be interim action. The manufacturer has advised that it currently is developing a modification that will address the unsafe condition addressed by this proposed AD. Once this modification is developed, approved, and available, we may consider additional rulemaking.

Costs of Compliance

There are about 321 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 255 airplanes of U.S. registry. The proposed actions would take about 2 work hours per airplane, at an average labor rate of $65 per work hour. Based on these figures, the estimated cost of the proposed AD for U.S. operators is $33,150, or $130 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 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. 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

2. The FAA amends § 39.13 by adding the following new airworthiness directive (AD):

Learjet: Docket No. FAA-2005-20947; Directorate Identifier 2004-NM-245-AD.

Comments Due Date

(a) The Federal Aviation Administration (FAA) must receive comments on this AD action by May 31, 2005.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Learjet Model 23, 24, 24A, 24B, 24B-A, 24D, 24D-A, 24E, 24F, 25, 25A, 25B, 25C, 25D, and 25F airplanes; certificated in any category; modified by Supplemental Type Certificate SA1731SW, SA1669SW, or SA1670SW; equipped with Nordam (formerly Dee Howard Company) thrust reversers having part number (P/N) 25-0570-127-1, -3, -7, -13, or -17.

Unsafe Condition

(d) This AD was prompted by reports of the failure of two thrust reverser accumulators. We are issuing this AD to prevent failure of the thrust reverser accumulators, due to fatigue cracking on the female threads, which could result in the loss of hydraulic power and damage to the surrounding airplane structure.

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.

Remove Thrust Reverser Accumulator

(f) Within 60 days after the effective date of this AD, remove the thrust reverser accumulator, and make the thrust reverser hydraulic system and the thrust reversers inoperable, by doing all of the actions specified in the Accomplishment Instructions of The Nordam Group Alert Service Bulletin A3000 78-21, dated November 25, 2002. Where there are differences between the Master Minimum Equipment List and the AD, the AD prevails. Although the service bulletin referenced in this AD specifies to submit certain information to the manufacturer, this AD does not include that requirement.

Parts Installation

(g) As of the effective date of this AD, no person may install a thrust reverser accumulator having P/N 25-0570-127-1, -3, -7, -13, or -17 on any airplane.

Alternative Methods of Compliance (AMOCs)

(h) The Manager, Special Certification Office, Rotorcraft Directorate, FAA, has the authority to approve AMOCs for this AD, if requested in accordance with the procedures found in 14 CFR 39.19.

Issued in Renton, Washington, on April 5, 2005. Kalene C. Yanamura,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.

References

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