AD 95-25-03

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Learjet Model 23, 24, 25, 35, and 36 airplanes. This action requires repetitive inspections to detect deterioration of both flapper valves of the tip tank in each wing of the airplane, and various follow-on actions. This AD action also requires replacing the flapper valves with new flapper valves, and repetitively performing certain other follow-on actions. This amendment is prompted by reports of imbalance of the fuel loads in the wings of the airplane due to failed or cracked flapper valves. The actions specified in this AD are intended to prevent significant reduction in the lateral control of the airplane due to imbalance of the fuel loads in the wings of the airplane.

Final rule; request for comments

95-25-03 LEARJET: Amendment 39-9447. Docket 95-NM-209-AD.

Applicability: Model 23, 24, and 25 airplanes, as listed in Learjet Service Bulletin SB 23/24/25-28-2, dated October 6, 1995, and Model 35 and 36 airplanes, as listed in Learjet Service Bulletin 35/36-28-10, dated October 6, 1995; certificated in any category.

NOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must use the authority provided in paragraph (e) of this AD to request approval from the FAA. This approval may address either no action, if the current configuration eliminates the unsafe condition; or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any airplane from the applicability of this AD.

Compliance: Required as indicated, unless accomplished previously.

NOTE 2: This AD references certain Learjet service bulletins for applicability information, and inspection and replacement procedures. This AD requires performing certain follow-on actions repetitively, although the service bulletins specify accomplishing these actions just once. Where there are differences between the AD and the service bulletins, the AD prevails.

To prevent imbalance of the fuel loads in the wings of the airplane, which can significantly reduce lateral control of the airplane, accomplish the following:

(a) Within 50 hours time-in-service after the effective date of this AD 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 flapper valves 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.

(b) Except as provided in paragraph (c) of this AD, at the later of the times specified in paragraphs (b)(1) and (b)(2) of this AD: Replace both flapper valves of the tip tank in each wing with new flapper valves 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) Within50 hours time-in-service after the effective date of this AD.

(c) For airplanes on which the age and time-in-service of the flapper valve cannot be determined: Within 50 hours time-in-service after the effective date of this AD, replace both flapper valves 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.

(d) 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 (a) of this AD.

(e) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Wichita Aircraft Certification Office (ACO), FAA, Small Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Wichita ACO.

NOTE 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Wichita ACO.

(f) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

(g) The actions shall be done in accordance with either Learjet Service Bulletin SB 23/24/25-28-2, dated October 6, 1995; or Learjet Service Bulletin SB 35/36-28-10, dated October 6, 1995; as applicable. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Learjet, Inc., One Learjet Way, Wichita, Kansas 67209-2942. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Wichita Aircraft Certification Office, Small Airplane Directorate, 1801 Airport Road, Room 100, Mid-Continent Airport, Wichita, Kansas; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(h) This amendment becomes effective on December 27, 1995.

Recently, the FAA has received several reports of imbalance of the fuel loads in the wings of Learjet Model 23, 24, 25, 35, and 36 airplanes. Investigation reveals that the flapper valves in the fuel tanks may deteriorate over a period of time, which may result in failure of the valve hinge or cracking of the circular portion of the valve. Further investigation indicates that such failures and cracking may allow fuel to enter into the tip tanks in the wings of the airplane. This condition, if not corrected, could result in imbalance of the fuel loads in the wings of the airplane, which can significantly reduce lateral control of the airplane.

The FAA has reviewed and approved Learjet Service Bulletins SB 23/24/25-28-2 (for Model 23, 24, and 25 airplanes) and SB 35/36-28-10 (for Model 35 and 36 airplanes), both dated October 6, 1995, which describe procedures for a one-time inspection to detect deterioration of both flapper valves of the tip tank ineach wing of the airplane, and various follow-on actions (which include inspecting the flapper valve to ensure proper positioning of the valve, inspecting the conditions of the screws that retain the flapper valve to the plate assembly, and ensuring that the flapper valve completely covers the opening of the tube and is seated against the tube). The service bulletins also describe procedures for replacement of both flapper valves of the tip tank in each wing with new flapper valves, and inspecting to verify free movement of the flapper valve.

Since an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design, this AD is being issued to prevent imbalance of fuel loads in the wings of the airplane, which can significantly reduce lateral control of the airplane. This AD requires that operators perform repetitive inspections to detect deterioration of both flapper valves of the tip tank in each wing of the airplane, and variousfollow-on actions (such as, inspecting the flapper valve to ensure proper positioning of the valve, inspecting the conditions of the screws that retain the flapper valve to the plate assembly, ensuring that the flapper valve completely covers the opening of the tube and is seated against the tube, and inspecting to verify free movement of the flapper valve). The AD requires that operators replace both flapper valves of the tip tank in each wing of the airplane with new flapper valves, and repetitively performing certain other follow-on actions. The actions are required to be accomplished in accordance with the procedures in the service bulletins described previously.

Operators should note that, although the service bulletins recommend that certain follow-on actions be accomplished only once, the FAA has determined that accomplishing these follow-on actions just one time would not address the identified unsafe condition over the long term. In developing the appropriate actions for this proposed AD, the FAA considered not only the manufacturer's recommendation, but the degree of urgency associated with addressing the subject unsafe condition, the potential catastrophic consequences of the unsafe condition, and the numerous reported incidents of unbalanced fuel loads. In light of all of these factors, the FAA finds that certain follow-on actions must be performed repetitively at intervals of 600 hours time-in-service to ensure continued operational safety of the fleet.

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.

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 95-NM-209-AD." The postcard will be date stamped and returned to the commenter.

The regulations adopted herein will not have substantial direct effects 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, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.

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."

List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

Adoption of the Amendment
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:

PART 39 - AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 USC 106(g), 40101, 40113, 44701.

39.13 - [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive: