Airworthiness Directives; Learjet Model 23, 24, 24A, 24B, 24B-A, 24C, 24D, 24D-A, 24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, 25F, 28, 29, 31, 31A, 35, 35A (C-21A), and 36 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 Learjet Model 23, 24, 24A, 24B, 24B-A, 24C, 24D, 24D-A, 24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, 25F, 28, 29, 31, 31A, 35, 35A (C-21A), and 36 airplanes. This proposed AD would require a one-time inspection of the center ball of the aileron control cable or cables for a defective swage, and corrective actions if necessary. This proposed AD is prompted by a report indicating that an aileron cable failed on one affected airplane when the cable underwent a tension check. We are proposing this AD to prevent severe weakening of the aileron cable, and consequent reduced controllability of the airplane.

DATES:

We must receive comments on this proposed AD by May 23, 2005.

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 Learjet, Inc., One Learjet Way, Wichita, Kansas 67209-2942.

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-2005-20872; the directorate identifier for this docket is 2004-NM-271-AD.

FOR FURTHER INFORMATION CONTACT:

David Hirt, 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) 946-4156; fax (316) 946-4107.

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-2005-20872; Directorate Identifier 2004-NM-271-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 website, 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 a report indicating that an aileron cable failed on a Learjet Model 35A (C-21A) airplane when the cable underwent a tension check while being installed. Further investigation showed that an over-sized ball was swaged onto the cable during manufacture. Swaging an over-sized ball onto a cable allows excess material into the swaging die, which causes the ball to over-swage and then sever the cable strands. This condition, if not corrected, could result in severe weakening of the aileron cable, and consequent reduced controllability of the airplane.

The subject area on Learjet Model 23, 24, 24A, 24B, 24B-A, 24C, 24D, 24D-A, 24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, 25F, 28, 29, 31, 31A, 35, and 36 airplanes is identical to those on the affected Model 35A (C-21A) airplane. Therefore, all these airplanes may be subject to the same unsafe condition.

Relevant Service Information

We have reviewed the Learjet service bulletins in the following table.

These service bulletins describe procedures for visually inspecting the center ball of the aileron control cable or cables for a defective swage, which includes an extruded shoulder and/or face deformation. If the inspection shows a defective swage, the service bulletins describe procedures for, among other actions, replacing the aileron cable with a new cable. The service bulletins also request that operators send to the manufacturer all defective parts, and a report indicating compliance with the applicable service bulletin. 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. Therefore, we are proposing this AD, which would require accomplishing the actions specified in the service information described previously, except as discussed under “Differences Between the Proposed AD and the Service Bulletins.”

Differences Between the Proposed AD and the Service Bulletins

Operators should note that, although the Accomplishment Instructions of the referenced service bulletin describe procedures for submitting a report showing compliance with the service bulletin and for returning any discrepant parts to the manufacturer, this proposed AD would not require those actions.

The service bulletins recommend that operators accomplish the actions “as soon as possible” within 10 flight hours after receiving the applicable service bulletin. This proposed AD would require that operators accomplish the actions within 100 flight hours, or 90 days after the effective date of the proposed AD, whichever occurs first. We find that the proposed compliance time addresses the unsafe condition soon enough to maintain an adequate level of safety for the affected fleet. In developing an appropriate compliance time for this AD we considered the degree of urgency associated with addressing the unsafe condition, and the maximum interval of time allowable for all affected airplanes to continue to operate without compromising safety.

Clarification of Inspection Language

The service bulletins describe procedures for “visually inspecting” the center ball of the aileron control cable or cables. In this proposed AD we refer to this inspection as a “detailed inspection.” Note 1 of this proposed AD defines this inspection.

Costs of Compliance

There are about 1,704 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 1,136 airplanes of U.S. registry. The proposed inspection would take about 1 work hour 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 $73,840, or $65 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.