[Federal Register Volume 60, Number 238 (Tuesday, December 12, 1995)]
[Rules and Regulations]
[Pages 63617-63619]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-29300]



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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 95-NM-209-AD; Amendment 39-9447; AD 95-25-03]


Airworthiness Directives; Learjet Model 23, 24, 25, 35, and 36 
Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule; request for comments.

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SUMMARY: 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.

DATES: Effective December 27, 1995.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of December 27, 1995.
    Comments for inclusion in the Rules Docket must be received on or 
before February 12, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 95-NM-209-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056.
    The service information referenced in this AD may be obtained from 
Learjet, Inc., One Learjet Way, Wichita, Kansas 67209-2942. This 
information may be examined 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.

FOR FURTHER INFORMATION CONTACT: Jeffrey Janusz, Aerospace Engineer, 
Systems and Propulsion Branch, ACE-116W, FAA, Wichita Aircraft 
Certification Office, Small Airplane Directorate, 1801 Airport Road, 
Room 100, Mid-Continent Airport, Wichita, Kansas 67209; telephone (316) 
946-4148; fax (316) 946-4407.

SUPPLEMENTARY INFORMATION: 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 

[[Page 63618]]
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 in each 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 various follow-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.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

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.


[[Page 63619]]

    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) Within 50 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.

    Issued in Renton, Washington, on November 27, 1995.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 95-29300 Filed 12-11-95; 8:45 am]
BILLING CODE 4910-13-U