[Federal Register Volume 70, Number 71 (Thursday, April 14, 2005)]
[Proposed Rules]
[Pages 19718-19720]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-7484]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2005-20947; Directorate Identifier 2004-NM-245-AD]
RIN 2120-AA64


Airworthiness Directives; Learjet Model 23, 24, 24A, 24B, 24B-A, 
24D, 24D-A, 24E, 24F, 25, 25A, 25B, 25C, 25D, and 25F Airplanes 
Modified by Supplemental Type Certificate SA1731SW, SA1669SW, or 
SA1670SW

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 23, 24, 24A, 24B, 24B-A, 24D, 24D-A, 24E, 
24F, 25, 25A, 25B, 25C, 25D, and 25F airplanes. This proposed AD would 
require removing the thrust reverser accumulator, and making the thrust 
reverser hydraulic system and the thrust reversers inoperable. This 
proposed AD is prompted by reports of the failure of two thrust 
reverser accumulators. We are proposing this AD to prevent failure of 
the thrust reverser accumulators, due to fatigue cracking on the female 
threads, which could result in the loss of hydraulic power and damage 
to the surrounding airplane structure.

DATES: We must receive comments on this proposed AD by May 31, 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.
     By 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 The 
Nordam Group, Nacelle/Thrust Reverser Systems Division, 6911 North 
Whirlpool Drive, Tulsa, OK 74117.
    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-2005-20947; the directorate identifier for this 
docket is 2004-NM-245-AD.

FOR FURTHER INFORMATION CONTACT: Jim Rankin, Aerospace Engineer, 
Special Certification Office, ASW-190, FAA, Rotorcraft Directorate, 
2601 Meacham Boulevard, Fort Worth, Texas, 76137-4298; telephone (817) 
222-5138; fax (817) 222-5785.

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-2005-20947; 
Directorate Identifier 2004-NM-245-AD'' in the subject line 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 submitted 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 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 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.

[[Page 19719]]

Discussion

    We have received reports indicating the failure of two thrust 
reverser accumulators, part number (P/N) 25-0570-127-7. One of the 
failures occurred in flight during final approach of an airplane and 
resulted in the loss of hydraulic power and damage to the airplane 
tailcone. The other failure occurred when a repair facility was proof 
testing an accumulator at 2,250 psig (the accumulator is rated for 
1,500 psig). Inspection of both of these thrust reverser accumulators 
found suspected fatigue cracking on the female threads where the halves 
are joined. This condition, if not corrected, could result in the loss 
of hydraulic power and damage to the surrounding airplane structure.
    The thrust reverser accumulators having P/N 25-0570-127-1, -3, -13, 
or -17 on certain Learjet Model 23, 24, 24A, 24B, 24B-A, 24D, 24D-A, 
24E, 24F, 25, 25A, 25B, 25C, 25D, and 25F airplanes are identical to 
those on the affected airplanes having P/N 25-0570-127-7. Therefore, 
all of these models with any of these part numbers may be subject to 
the same unsafe condition.

Relevant Service Information

    We have reviewed The Nordam Group Alert Service Bulletin A3000 78-
21, dated November 25, 2002. The service bulletin describes procedures 
for removing the thrust reverser accumulator, and making the thrust 
reverser hydraulic system and the thrust reversers inoperable.

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. Therefore, we are proposing this AD, which 
would require accomplishing the actions specified in the service 
information described previously, except as discussed under 
``Difference Between the Proposed AD and Service Bulletin.''

Differences Between the Proposed AD and Service Bulletin

    Operators should note that, although the service bulletin specifies 
the compliance time as ``not later than 10 flight-hours from receipt of 
this alert service bulletin,'' this proposed AD specifies a compliance 
time of ``within 60 days after the effective date of this AD.'' In 
developing an appropriate compliance time for this AD, the FAA 
considered not only the manufacturer's recommendation, but the degree 
of urgency associated with addressing the subject unsafe condition, the 
average utilization of the affected fleet, and the time necessary to 
perform the actions required by the proposed AD. In light of all of 
these factors, the FAA finds a compliance time of 60 days for 
completing the required actions to be warranted, in that it represents 
an appropriate interval of time for affected airplanes to continue to 
operate without compromising safety. This difference has been 
coordinated with the manufacturer.
    Operators should note that, although the Accomplishment 
Instructions of the referenced service bulletin describe procedures for 
submitting a comment sheet recording compliance with the service 
bulletin, this proposed AD would not require that action. We do not 
need this information from operators.

Interim Action

    This is considered to be interim action. The manufacturer has 
advised that it currently is developing a modification that will 
address the unsafe condition addressed by this proposed AD. Once this 
modification is developed, approved, and available, we may consider 
additional rulemaking.

Costs of Compliance

    There are about 321 airplanes of the affected design in the 
worldwide fleet. This proposed AD would affect about 255 airplanes of 
U.S. registry. The proposed actions would take about 2 work hours per 
airplane, at an average labor rate of $65 per work hour. Based on these 
figures, the estimated cost of the proposed AD for U.S. operators is 
$33,150, or $130 per airplane.

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 adding the following new 
airworthiness directive (AD):

Learjet: Docket No. FAA-2005-20947; Directorate Identifier 2004-NM-
245-AD.

Comments Due Date

    (a) The Federal Aviation Administration (FAA) must receive 
comments on this AD action by May 31, 2005.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Learjet Model 23, 24, 24A, 24B, 24B-A, 
24D, 24D-A, 24E, 24F, 25, 25A, 25B, 25C, 25D, and 25F airplanes; 
certificated in any category; modified by Supplemental Type 
Certificate SA1731SW, SA1669SW, or SA1670SW; equipped with Nordam 
(formerly Dee Howard Company) thrust reversers having part number 
(P/N) 25-0570-127-1, -3, -7, -13, or -17.

[[Page 19720]]

Unsafe Condition

    (d) This AD was prompted by reports of the failure of two thrust 
reverser accumulators. We are issuing this AD to prevent failure of 
the thrust reverser accumulators, due to fatigue cracking on the 
female threads, which could result in the loss of hydraulic power 
and damage to the surrounding airplane structure.

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.

Remove Thrust Reverser Accumulator

    (f) Within 60 days after the effective date of this AD, remove 
the thrust reverser accumulator, and make the thrust reverser 
hydraulic system and the thrust reversers inoperable, by doing all 
of the actions specified in the Accomplishment Instructions of The 
Nordam Group Alert Service Bulletin A3000 78-21, dated November 25, 
2002. Where there are differences between the Master Minimum 
Equipment List and the AD, the AD prevails. Although the service 
bulletin referenced in this AD specifies to submit certain 
information to the manufacturer, this AD does not include that 
requirement.

Parts Installation

    (g) As of the effective date of this AD, no person may install a 
thrust reverser accumulator having P/N 25-0570-127-1, -3, -7, -13, 
or -17 on any airplane.

Alternative Methods of Compliance (AMOCs)

    (h) The Manager, Special Certification Office, Rotorcraft 
Directorate, FAA, has the authority to approve AMOCs for this AD, if 
requested in accordance with the procedures found in 14 CFR 39.19.

    Issued in Renton, Washington, on April 5, 2005.
Kalene C. Yanamura,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 05-7484 Filed 4-13-05; 8:45 am]
BILLING CODE 4910-13-P