05-6579. Airworthiness Directives; Learjet Model 23, 24, 25, 35, and 36 Airplanes

AGENCY:

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

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Learjet Model 23, 24, 25, 35, and 36 airplanes. The existing AD currently requires repetitive inspections to detect deterioration of both flappers of the tip tank in each wing of the airplane, and various follow-on actions. The existing AD also requires replacing the flappers with new flappers, and repetitively performing certain other follow-on actions. This proposed AD would require an inspection of the flappers and flapper assemblies of the tip tank in each wing or a review of the airplane maintenance records to determine the part numbers, and replacement of certain flappers or flapper assemblies if necessary, which would end the existing repetitive inspections. This proposed AD is prompted by the results of numerous continual inspections, and the approval of a new, improved flapper and flapper assembly. We are proposing this AD to prevent significant reduction in the lateral control of the airplane due to imbalance of the fuel loads in the wings of the airplane.

DATES:

We must receive comments on this proposed AD by May 19, 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.
• Fax: [phone].
• 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-2005-20798; the directorate identifier for this docket is 2004-NM-257-AD.

FOR FURTHER INFORMATION CONTACT:

Jeffrey Janusz, 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 [phone]; fax [phone].

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-2005-20798; Directorate Identifier 2004-NM-257-AD” at the beginning 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 received 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 our docket 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 the 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 [phone]) 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

On November 27, 1995, we issued AD 95-25-03, amendment 39-9447 (60 FR 63617, December 12, 1995), for certain Learjet Model 23, 24, 25, 35, and 36 airplanes. That AD requires repetitive inspections to detect deterioration of both flappers of the tip tank in each wing of the airplane, and various follow-on actions. That AD also requires replacing the flappers with new flappers, and repetitively performing certain other follow-on actions. That AD was prompted by reports of imbalance of the fuel loads in the wings of the airplane due to failed or cracked flappers. We issued that AD to prevent significant reduction in the lateral control of the airplane due to imbalance of the fuel loads in the wings of the airplane.

Actions Since Existing AD Was Issued

Since we issued AD 95-25-03, we have reviewed Learjet Service Bulletin 23/24/25-28-7, Revision 2, dated May 9, 2001 (for Model 23, 24, and 25 airplanes); and Learjet Service Bulletin 35/36-28-14, Revision 2, dated May 9, 2001 (for Model 35 and 36 airplanes). The service bulletins describe procedures for replacing flappers with new flappers or replacing the flapper assemblies with new or modified and reidentified assemblies, which eliminates the need for the repetitive inspections required by AD 95-25-03. 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

The unsafe condition described previously is likely to exist or develop on other airplanes of the same type design that may be registered in the U.S. at some time in the future.

We can better ensure long-term continued operational safety by design changes to remove the source of the problem, rather than by repetitive inspections. Long-term inspections, as required by AD 95-25-03, may not provide the degree of safety necessary for the transport airplane fleet. This determination, along with a better understanding of the human factors and other systems effects associated with numerous continual inspections, has led us to consider placing less emphasis on inspections and more emphasis on design improvements. The proposed replacement requirement is consistent with these conditions.

We are proposing to supersede AD 95-25-03. This proposed AD would retain the requirements of the existing AD. This proposed AD would also require accomplishing the actions specified in service bulletins described previously in this proposed AD, which would end the repetitive inspection requirements of the existing AD. This proposed AD would also require an inspection of the flappers and flapper assemblies of the tip tank in each wing, or a review of the airplane maintenance records, to determine the part numbers.

Change to Existing AD

This proposed AD would retain all requirements of AD 95-25-03. Since AD 95-25-03 was issued, the AD format has been revised, and certain paragraphs have been rearranged. As a result, the corresponding paragraph identifiers have changed in this proposed AD, as listed in the following table:

Revised Paragraph Identifiers

Requirements in AD 95-25-03	Corresponding requirement in this proposed AD
Paragraph (a)	Paragraph (f).
Paragraph (b)	Paragraph (g).
Paragraph (c)	Paragraph (h).
Paragraph (d)	Paragraph (i).

Costs of Compliance

There are about 1,459 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 882 airplanes of U.S. registry.

The actions that are required by AD 95-25-03 and retained in this proposed AD take about 16 work hours per airplane, at an average labor rate of $65 per work hour. Required parts cost about $708 per airplane. Based on these figures, the estimated cost of the currently required actions is $1,541,736, or $1,748 per airplane.

The new proposed actions would take about 2 work hours per airplane, at an average labor rate of $65 per work hour. Required parts would cost about $327 or $1,262 per airplane (depending on the kit installed). Based on these figures, the estimated cost of the new actions specified in this proposed AD for U.S. operators is $457 or $1,392, per airplane (depending on the kit installed).

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

[Amended]

2. The FAA amends § 39.13 by removing amendment 39-9447 (60 FR 63617, December 12, 1995) and adding the following new airworthiness directive (AD):

Learjet: Docket No. FAA-2005-20798; Directorate Identifier 2004-NM-257-AD.

Comments Due Date

(a) The Federal Aviation Administration must receive comments on this AD action by May 19, 2005.

Affected ADs

(b) This AD supersedes AD 95-25-03, amendment 39-9447 (60 FR 63617, December 12, 1995).

Applicability

(c) This AD applies to the airplanes in Table 1 of this AD, certificated in any category.

Table 1.—Applicability

Learjet—	Serial Nos.
Model 23 airplanes	23-003 through 23-090 inclusive.
Model 24 airplanes	24-100 through 24-357 inclusive.
Model 25 airplanes	25-002 through 25-373 inclusive.
Model 35 airplanes	35-002 through 35-676 inclusive.
Model 36 airplanes	36-002 through 36-063 inclusive.

Unsafe Condition

(d) This AD was prompted by the results of numerous continual inspections, and the approval of a new, improved flapper and flapper assembly. We are issuing this AD to prevent significant reduction in the lateral control of the airplane due to imbalance of the fuel loads in the wings of the airplane.

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.

Requirements of AD 95-25-03

Repetitive Inspections, Related Investigative Actions, and Replacement

(f) Within 50 hours time-in-service after December 27, 1995 (the effective date of AD 95-25-03), or prior to the accumulation of 600 hours time-in-service since installation of the flapper valve, whichever occurs later: Perform an inspection to detect deterioration (such as cracks, cuts, breaks, splits, or warpage) of both flappers of the tip tank in each wing, in accordance with either Learjet Service Bulletin SB 23/24/25-28-2, dated October 6, 1995 (for Model 23, 24, and 25 airplanes), or Learjet Service Bulletin SB 35/36-28-10, dated October 6, 1995 (for Model 35 and 36 airplanes); as applicable. Repeat this inspection thereafter at intervals not to exceed 600 hours time-in-service.

(1) If no deterioration of the flapper valve is detected, prior to further flight, inspect the flapper valve to ensure proper positioning, inspect the condition of the screws that retain the flapper valve to the plate assembly to ensure that the flapper valve is secure, inspect to ensure that the flapper valve completely covers the opening of the tube and is seated against the tube, and inspect the flapper valve to verify that it moves freely; and accomplish the follow-on corrective actions, if any discrepancy is found. These actions shall be accomplished in accordance with the applicable service bulletin.

(2) If any flapper valve is found to be deteriorated, prior to further flight, replace it with a new flapper valve in accordance with the applicable service bulletin.

(g) Except as provided in paragraph (h) of this AD, at the later of the times specified in paragraphs (g)(1) and (g)(2) of this AD: Replace both flappers of the tip tank in each wing with new flappers in accordance with either Learjet Service Bulletin SB 23/24/25-28-2, dated October 6, 1995 (for Model 23, 24, and 25 airplanes), or Learjet Service Bulletin SB 35/36-28-10, dated October 6, 1995 (for Model 35 and 36 airplanes); as applicable.

(1) Within 5 years since date of installation of the flapper valve, or prior to the accumulation of 2,400 total hours time-in-service on the flapper valve, whichever occurs earlier.

(2) Within 50 hours time-in-service after December 27, 1995.

(h) For airplanes on which the age and time-in-service of the flapper valve cannot be determined: Within 50 hours time-in-service after December 27, 1995, replace both flappers of the tip tank in each wing in accordance with either Learjet Service Bulletin SB 23/24/25-28-2, dated October 6, 1995 (for Model 23, 24, and 25 airplanes), or Learjet Service Bulletin SB 35/36-28-10, dated October 6, 1995 (for Model 35 and 36 airplanes); as applicable.

(i) Within 600 hours time-in-service following replacement of any flapper valve in accordance with the requirements of this AD, and thereafter at intervals not to exceed 600 hours time-in-service: Accomplish the requirements of paragraph (f) of this AD.

New Requirements

Inspection and Replacement

(j) Within 600 hours time-in-service since last replacement of any flapper valve in accordance with the requirements of this AD, or within 90 days after the effective date of this AD, whichever occurs later, inspect the flappers and flapper assemblies of the tip tank in each wing to determine their part numbers (P/N). The raised letter and numbers “S-461” on the convex side of the flappers can identify these parts. Instead of inspecting the flappers and flapper assemblies, a review of airplane maintenance records is acceptable if the P/N of the flappers and flapper assemblies can be conclusively determined from that review.

(1) If four flappers having P/N 2323006-802 and four flapper assemblies having P/N 2323006-801 are found installed, no further action is required by this paragraph, and the repetitive inspections required by paragraphs (f) and (i) of this AD can be stopped.

(2) If any flapper having P/N 2323006-5 or any flapper assembly having P/N 2323006-6 is found installed, within 600 hours time-in-service since last replacement of any flapper valve in accordance with the requirements of this AD, replace the flapper valve with a new flapper valve or replace the flapper assembly with new or modified and reidentified assembly, as applicable. The replacement must be done in accordance with the Accomplishment Instructions of Learjet Service Bulletin 23/24/25-28-7, Revision 2, dated May 9, 2001 (for Model 23, 24, and 25 airplanes); or Learjet Service Bulletin 35/36-28-14, Revision 2, dated May 9, 2001 (for Model 35 and 36 airplanes); as applicable. Accomplishment of the replacement ends the repetitive inspections required by paragraphs (f) and (i) of this AD.

Parts Installation

(k) As of the effective date of this AD, no person may install a flapper having P/N 2323006-5 or a flapper assembly having P/N 2323006-6, on any airplane.

Alternative Methods of Compliance (AMOCs)

(l)(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) AMOCs approved previously according to AD 95-25-03 are not approved as AMOCs with this AD.

Issued in Renton, Washington, on March 22, 2005.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.