[Federal Register Volume 70, Number 63 (Monday, April 4, 2005)]
[Proposed Rules]
[Pages 16984-16986]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-6579]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2005-20798; Directorate Identifier 2004-NM-257-AD]
RIN 2120-AA64


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).

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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: (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-2005-20798; 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 (316) 946-4148; 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-2005-20798; 
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 (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

    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

[[Page 16985]]

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
------------------------------------------------------------------------
                                           Corresponding  requirement in
      Requirements in  AD 95-25-03               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.


Sec.  39.13  [Amended]

    2. The FAA amends Sec.  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

[[Page 16986]]

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.
[FR Doc. 05-6579 Filed 4-1-05; 8:45 am]
BILLING CODE 4910-13-P