[Federal Register Volume 72, Number 80 (Thursday, April 26, 2007)]
[Proposed Rules]
[Pages 20775-20777]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E7-8001]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2007-28016; Directorate Identifier 2006-NM-227-AD]
RIN 2120-AA64


Airworthiness Directives; Learjet Model 31, 31A, 35, 35A (C-21A), 
36, 36A, 55, 55B, and 55C Airplanes, and Model 45 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 adopt a new airworthiness directive (AD) 
for certain Learjet Model 31, 31A, 35, 35A (C-21A), 36, 36A, 55, 55B, 
and 55C airplanes, and Model 45 airplanes. This proposed AD would 
require inspecting for unsealed gaps on the pylon side of the engine 
firewall and cleaning/sealing any unsealed gap; and, for certain 
airplanes, inspecting for unsealed gaps of the pylon trailing edge and 
cleaning/sealing any gap. This proposed AD results from a report that 
unsealed gaps (penetration points) of the engine firewall were 
discovered during production. We are proposing this AD to prevent 
penetration of flammable liquids or fire through the engine firewall 
into the engine pylon, which could lead to fire inside the airplane.

DATES: We must receive comments on this proposed AD by June 11, 2007.

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.
    Contact Learjet, Inc., One Learjet Way, Wichita, Kansas 67209-2942, 
for the service information identified in this proposed AD.

FOR FURTHER INFORMATION CONTACT: James Galstad, 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) 946-4135; 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 in the ADDRESSES section. Include the docket number ``FAA-2007-
28016; Directorate Identifier 2006-NM-227-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 
that web site, anyone can find and read the

[[Page 20776]]

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 may review DOT's 
complete Privacy Act Statement in the Federal Register published on 
April 11, 2000 (65 FR 19477-78), or you may visit http://dms.dot.gov.

Examining the Docket

    You may 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 Docket Management System 
receives them.

Discussion

    We have received a report indicating that the engine firewall 
sealing application on certain Learjet Model 45 airplanes does not meet 
engineering standards, as unsealed gaps (penetration points) of the 
engine firewall were discovered during production. Further 
investigation revealed that the same condition could be present on 
Model 31, 31A, 35, 35A (C-21A), 36, 36A, 55, 55B, and 55C airplanes. 
Such gaps could include those provided for bleed air, anti-ice, fuel, 
and fire extinguishing systems, as well as engine mounts, control 
cables, access panels, and others not described. This condition, if not 
corrected, could result in penetration of flammable liquids or fire 
through the engine firewall into the engine pylon, which could lead to 
fire inside the airplane.

Relevant Service Information

    We have reviewed the service bulletins specified in the following 
table. For all airplanes, the service bulletins describe procedures for 
inspecting for unsealed gaps on the pylon side of the engine firewall 
and cleaning/sealing any unsealed gap. For Model 45 airplanes only, 
Service Bulletin 45-54-3 also describes procedures for inspecting for 
unsealed gaps on the pylon trailing edge and cleaning/sealing any 
unsealed gap. Accomplishing the actions specified in the service 
information is intended to adequately address the unsafe condition.

                                         Applicable Service Information
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     Learjet airplane model          Service bulletin          Revision level                   Date
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31/31A.........................  Bombardier Service       1......................  August 21, 2006.
                                  Bulletin 31-54-2.
45.............................  Bombardier Service       2......................  August 15, 2003.
                                  Bulletin 45-54-3.
35/35A (C-21A) and 36/36A......  Learjet Service          Original...............  March 16, 2001.
                                  Bulletin 35/36-54-3.
55/55B/55C.....................  Learjet Service          Original...............  March 16, 2001.
                                  Bulletin 55-54-3.
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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. For this reason, we are proposing this AD, 
which would require accomplishing the actions specified in the service 
information described previously.

Costs of Compliance

    There are about 1,243 airplanes of the affected design in the 
worldwide fleet. This proposed AD would affect about 945 airplanes of 
U.S. registry. The following table provides the estimated costs for 
U.S. operators to comply with this proposed AD, at an average labor 
rate of $80 per work hour. Parts and materials may be supplied from 
operator stores or procured locally.

                             Estimated Costs to Perform Inspection and Modifications
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                                                                                  Number of U.S.-
             Learjet airplane model                 Work hours       Cost per       registered      Fleet cost
                                                                     airplane        airplanes
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31/31A..........................................               2            $160             173         $27,680
35/35A (C-21A)..................................               2             160             507          81,120
36/36A..........................................               2             160              42           6,720
45..............................................               5             400             102          40,800
55/55B/55C......................................               2             160             121          19,360
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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

[[Page 20777]]

    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 and placed it in the AD docket. 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 Federal Aviation Administration (FAA) amends Sec.  39.13 by 
adding the following new airworthiness directive (AD):

LEARJET: Docket No. FAA-2007-28016; Directorate Identifier 2006-NM-
227-AD.

Comments Due Date

    (a) The FAA must receive comments on this AD action by June 11, 
2007.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Learjet Model 31, 31A, 35, 35A (C-21A), 
36, 36A, 55, 55B, and 55C airplanes, and Model 45 airplanes; 
certificated in any category; as identified in the service 
information specified in Table 1 of this AD.

                                    Table 1.--Applicable Service Information
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     Learjet airplane model          Service bulletin          Revision level                   Date
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31/31A.........................  Bombardier Service       1......................  August 21, 2006.
                                  Bulletin 31-54-2.
45.............................  Bombardier Service       2......................  August 15, 2003.
                                  Bulletin 45-54-3.
35/35A (C-21A) and 36/36A......  Learjet Service          Original...............  March 16, 2001.
                                  Bulletin 35/36-54-3.
55/55B/55C.....................  Learjet Service          Original...............  March 16, 2001.
                                  Bulletin 55-54-3.
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Unsafe Condition

    (d) This AD results from a report that unsealed gaps 
(penetration points) of the engine firewall were discovered during 
production. We are issuing this AD to prevent penetration of 
flammable liquids or fire through the engine firewall into the 
engine pylon, which could lead to fire inside 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.

Inspecting, Cleaning, and Sealing of Gaps in Engine Firewall

    (f) Within 12 months after the effective date of this AD, do the 
actions described in paragraphs (f)(1) and (f)(2) of this AD, in 
accordance with the applicable service information specified in 
Table 1 of this AD.
    (1) For all airplanes: Inspect for unsealed gaps on the pylon 
side of the engine firewall and clean and seal any unsealed gap.
    (2) For Learjet Model 45 airplanes only: Inspect the engine 
pylon trailing edge for unsealed gaps, and clean and seal any 
unsealed gap.

Credit for Actions Done Using Previous Service Information

    (g) Actions accomplished before the effective date of this AD 
according to Bombardier Service Bulletin 31-54-2, dated March 16, 
2001; or Bombardier Service Bulletin 45-54-3, dated March 16, 2001; 
or Revision 1, dated December 12, 2001; as applicable; are 
considered acceptable for compliance with the corresponding action 
specified in this AD.

Alternative Methods of Compliance (AMOCs)

    (h)(1) The Manager, Wichita Aircraft Certification Office (ACO), 
FAA, has the authority to approve AMOCs for this AD, if requested in 
accordance with the procedures found in 14 CFR 39.19.
    (2) To request a different method of compliance or a different 
compliance time for this AD, follow the procedures in 14 CFR 39.19. 
Before using any approved AMOC on any airplane to which the AMOC 
applies, notify your appropriate principal inspector (PI) in the FAA 
Flight Standards District Office (FSDO), or lacking a PI, your local 
FSDO.

    Issued in Renton, Washington, on April 19, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
 [FR Doc. E7-8001 Filed 4-25-07; 8:45 am]
BILLING CODE 4910-13-P