[Federal Register Volume 70, Number 162 (Tuesday, August 23, 2005)]
[Proposed Rules]
[Pages 49210-49212]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-16752]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2005-22169; Directorate Identifier 2005-NM-094-AD]
RIN 2120-AA64


Airworthiness Directives; Learjet Model 23, 24, 24A, 24B, 24B-A, 
24C, 24D, 24D-A, 24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, and 25F 
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 23, 24, 24A, 24B, 24B-A, 24C, 24D, 24D-A, 
24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, and 25F airplanes. This 
proposed AD would require replacement of the spherical accumulator for 
the main hydraulic system with a new cylindrical accumulator. For 
certain airplanes, this proposed AD would also require modification of 
the accumulator pressure gauge. This proposed AD is prompted by reports 
of the failure of two thrust reverser accumulators (which are similar 
to the main hydraulic system's spherical accumulator) and fatigue 
cracks found on four thrust reverser accumulators. We are proposing 
this AD to prevent failure of the spherical accumulator for the main 
hydraulic system, due to fatigue cracking on the threads, which could 
result in the loss of hydraulic power, damage to the surrounding 
airplane structure, and loss of airplane control. The failure of the 
accumulator could also result in injury to any persons in the 
surrounding area. The loss of hydraulic fluid could also leak onto a 
potential source of ignition and result in a consequent fire.

DATES: We must receive comments on this proposed AD by October 7, 2005.

[[Page 49211]]


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 
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-2005-22169; the directorate identifier for this docket is 
2005-NM-094-AD.

FOR FURTHER INFORMATION CONTACT: Robert Busto, 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) 946-4157; 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-2005-22169; 
Directorate Identifier 2005-NM-094-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 website, 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 Docket Management System 
(DMS) receives them.

Discussion

    We have received a report indicating that two failures of thrust 
reverser accumulators occurred, and inspections have found four thrust 
reverser accumulators with fatigue cracks. One failure occurred during 
flight on a Learjet Model 25B airplane and led to an emergency landing. 
The second failure occurred during bench testing and resulted in injury 
to a person. Detailed inspections of four thrust reverser accumulators 
found fatigue cracks on the inner threads that hold the two halves of 
the accumulator together. The spherical accumulator used for the main 
airplane hydraulic system is similar to the spherical accumulator used 
for the thrust reverser hydraulic system. Therefore, these spherical 
accumulators may be subject to the same unsafe condition. This fatigue 
cracking, if not corrected, could result in the failure of the 
accumulator, which could cause loss of hydraulic fluid and the 
hydraulic systems, resulting in a loss of airplane control. The failure 
of the accumulator could also result in damage to the surrounding 
airplane structure and injury to any persons in the surrounding area. 
The loss of hydraulic fluid could also leak onto a potential source of 
ignition and result in a consequent fire.

Other Relevant Rulemaking

    We have published a notice of proposed rulemaking (NPRM) in the 
Federal Register on April 14, 2005 (70 FR 19718), applicable to 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; equipped with certain Nordam thrust 
reversers. That NPRM proposed to require removing the thrust reverser 
accumulator, and making the thrust reverser hydraulic system and the 
thrust reversers inoperable. The actions proposed in that NPRM are 
intended 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.

Relevant Service Information

    We have reviewed Bombardier Alert Service Bulletin A23/24/25-29-4, 
Revision 1, dated January 17, 2005. The service bulletin describes 
procedures for replacing certain spherical accumulators with new 
cylindrical accumulators, and reporting accomplishment of the service 
bulletin to the manufacturer. Replacing the accumulators may involve 
replacing the supports and attachment hardware.
    For certain airplanes, Bombardier Alert Service Bulletin A23/24/25-
29-4 recommends prior or concurrent accomplishment of Learjet Service 
Kit SK23-215, dated April 4, 1966. The concurrent service bulletin 
describes procedures for relocating the accumulator pressure gauge.
    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

    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 
``Differences Between the Proposed AD and the Service Bulletin.''

Differences Between the Proposed AD and the Service Bulletin

    Although Bombardier Alert Service Bulletin A23/24/25-29-4, Revision 
1, dated January 17, 2005, recommends replacing the spherical 
accumulator for the main hydraulic system within 25 flight hours after 
the receipt of the service bulletin, this proposed AD specifies a 
compliance time of 60 days after the effective date of the AD. In 
developing an appropriate compliance

[[Page 49212]]

time for this AD, we considered the manufacturer's recommendation, the 
degree of urgency associated with 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, we find that a longer compliance time represents an 
appropriate interval of time for affected airplanes to continue to 
operate without compromising safety. This difference has been 
coordinated with Learjet.
    Operators should also note that, although the Accomplishment 
Instructions of the referenced service bulletin describe procedures for 
submitting a comment sheet related to service bulletin quality and a 
sheet recording compliance with the service bulletin, this proposed AD 
would not require those actions. We do not need this information from 
operators.

Costs of Compliance

    There are about 434 airplanes of the affected design in the 
worldwide fleet. This proposed AD would affect about 242 airplanes of 
U.S. registry. The proposed actions would take about 9 to 13 work hours 
per airplane, at an average labor rate of $65 per work hour. Required 
parts would cost about $1,336 to $1,363 per airplane. Based on these 
figures, the estimated cost of the proposed AD for U.S. operators is 
$464,882 to $534,336, or $1,921 to $2,208 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-2005-22169; Directorate Identifier 2005-NM-
094-AD.

Comments Due Date

    (a) The Federal Aviation Administration (FAA) must receive 
comments on this AD action by October 7, 2005.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Learjet Model 23, 24, 24A, 24B, 24B-A, 
24C, 24D, 24D-A, 24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, and 25F 
airplanes, certificated in any category; having serial numbers 23-
003 through 23-099 inclusive, 24-100 through 24-284 inclusive, and 
25-003 through 25-153 inclusive.

Unsafe Condition

    (d) This AD was prompted by reports of the failure of two thrust 
reverser accumulators (which are similar to the main hydraulic 
system's accumulator) and fatigue cracks found on four thrust 
reverser accumulators. We are issuing this AD to prevent failure of 
the spherical accumulator for the main hydraulic system, due to 
fatigue cracking on the threads, which could result in the loss of 
hydraulic power, damage to the surrounding airplane structure, and 
loss of airplane control. The failure of the accumulator could also 
result in injury to any persons in the surrounding area. The loss of 
hydraulic fluid could also leak onto a potential source of ignition 
and result in a consequent fire.

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.

Replacement

    (f) Within 60 days after the effective date of this AD, replace 
the spherical accumulator having part number (P/N) 2380025-( ) or P/
N 2380167-( ) with a new cylindrical accumulator having P/N 2497202-
801 in accordance with the Accomplishment Instructions of Bombardier 
Alert Service Bulletin A23/24/25-29-4, Revision 1, dated January 17, 
2005.

Concurrent Action

    (g) For airplanes having serial numbers 23-003 through 23-014 
inclusive: Prior to or concurrently with the actions in Bombardier 
Alert Service Bulletin A23/24/25-29-4, Revision 1, dated January 17, 
2005, relocate the accumulator pressure gauge in accordance with 
Learjet Service Kit SK23-215, dated April 4, 1966.

Parts Installation

    (h) As of the effective date, no spherical accumulator having P/
N 2380025-() or P/N 2380167-() may be installed on any airplane.

Previous Actions

    (i) Replacements done before the effective date of this AD in 
accordance with Bombardier Alert Service Bulletin A23/24/25-29-4, 
dated August 20, 2004, are acceptable for compliance with the 
requirements of paragraph (f) of this AD.

No Reporting Required

    (j) Although the service bulletin referenced in this AD 
specifies to submit certain information to the manufacturer, this AD 
does not include that requirement.

Alternative Methods of Compliance (AMOCs)

    (k) 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.

    Issued in Renton, Washington, on August 12, 2005.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 05-16752 Filed 8-22-05; 8:45 am]
BILLING CODE 4910-13-P