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

[Federal Register Volume 70, Number 218 (Monday, November 14, 2005)]
[Rules and Regulations]
[Pages 69059-69061]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-22215]


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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; 
Amendment 39-14364; AD 2005-23-06]
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: Final rule.

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SUMMARY: The FAA is adopting 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 AD requires removing 
the thrust reverser accumulator, and making the thrust reverser 
hydraulic system and the thrust reversers inoperable. This AD results 
from 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.

DATES: This AD becomes effective December 19, 2005.
    The Director of the Federal Register approved the incorporation by 
reference of a certain publication listed in the AD as of December 19, 
2005.

ADDRESSES: You may examine the 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., Nassif Building, 
Room PL-401, Washington, DC.
    Contact The Nordam Group, Nacelle/Thrust Reverser Systems Division, 
6911 North Whirlpool Drive, Tulsa, Oklahoma 74117, for service 
information identified in this 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:

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 street address stated in the 
ADDRESSES section.

Discussion

    The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 
CFR part 39 to include an AD that would apply to certain Learjet Model 
23, 24, 24A, 24B, 24B-A, 24D, 24D-A, 24E, 24F, 25, 25A, 25B, 25C, 25D, 
and 25F airplanes. That NPRM was published in the Federal Register on 
April 14, 2005 (70 FR 19718). That NPRM proposed to require removing 
the thrust reverser accumulator, and making the thrust reverser 
hydraulic system and the thrust reversers inoperable.

Comments

    We provided the public the opportunity to participate in the 
development of this AD. We have considered the comments received.

Request To Withdraw NPRM

    One commenter does not support the NPRM. The commenter asserts that 
deactivating the thrust reversers will cause more accidents, especially 
under wet or winter runway conditions. The commenter also asserts that 
one in-flight failure of a thrust reverser does not justify the NPRM 
given the countless safe operations without thrust reverser failures. 
The commenter states that ``[the FAA] also [has] not looked or measured 
the increase of accidents that will be caused by this [NPRM].'' As 
further justification for not supporting the NPRM, the commenter states 
that the NPRM does not account for the cost of brake and tire wear that 
would be incurred if the thrust reversers are deactivated. We infer 
that the commenter would like us to withdraw the NPRM.
    We do not agree, since we have determined that an unsafe condition 
exists, and that the interim actions of this AD are necessary to ensure 
the continued safety of the affected fleet. The one thrust reverser 
failure on a Learjet Model 25B airplane that occurred in flight led to 
an emergency landing. A second failure occurred during proof testing 
and resulted in injury to a person. We acknowledge the commenter's 
concern with deactivating the thrust reversers; however, the affected 
Model 23, 24, 24A, 24B, 24B-A, 24D, 24D-A, 24E, 24F, 25, 25A, 25B, 25C, 
25D, and 25F airplanes were not originally type certificated with 
thrust reversers installed. Furthermore, we estimate that half of these 
Learjet model airplanes in service today are operating without thrust 
reversers. Therefore, an increase in accidents due to deactivation of 
the affected thrust reversers is unlikely.
    Regarding the cost impact of this AD, we point out that the 
economic analysis of the AD is limited only to the cost of actions 
actually required by the AD; it does not include incidental costs. In 
any case, we have determined that direct and incidental costs are 
outweighed by the safety benefits of this AD. Therefore, no change to 
this AD is necessary in this regard.

Request To Revise Requirements of NPRM

    Two commenters request that we revise the NPRM to require 
repetitive nondestructive testing or x-ray inspections of the thrust 
reverser accumulator, instead of proposing to deactivate the thrust 
reversers. One of the commenters states that inspection of the 
suspected point of failure (the female threads of the accumulator) 
would be sufficient to prevent failure of the thrust reverser 
accumulator. The commenter suggests that deactivation of the thrust 
reversers could be required if damage is found during an inspection.
    We do not agree, since the commenters provide no technical 
justification for revising the requirements of this AD. The history of 
crack growth on the affected thrust reversers is unknown. In addition, 
there have been no studies done to determine an appropriate inspection 
interval for providing an acceptable level of safety. As stated in the 
NPRM, the parts manufacturer currently is developing a modification 
that will address the unsafe condition of this AD. Once this 
modification is developed, approved, and available, we may consider 
additional rulemaking. Therefore no change to this AD is necessary in 
this regard.

Request To Expand Applicability

    One commenter, the parts manufacturer, requests that we delete 
reference to Supplemental Type Certificates (STCs) SA1731SW, SA1669SW, 
and SA1670SW from the

[[Page 69060]]

applicability of the NPRM. The commenter states this change will ensure 
that the NPRM is also applicable to other Learjet Model 23, 24, 24A, 
24B, 24B-A, 24D, 24D-A, 24E, 24F, 25, 25A, 25B, 25C, 25D, and 25F 
airplanes equipped with the affected thrust reverser accumulators. As 
an example, the commenter mentions that Model 24, 24B, 24D, 24F, 25, 
25B, 25C, and 25D airplanes modified by STC SA944NW are also equipped 
with the affected thrust reverser accumulators, but are not included in 
the applicability of the NPRM.
    We do not agree. We have determined that Model 24, 24B, 24D, 24F, 
25, 25B, 25C, and 25D airplanes modified by STC SA944NW do not need to 
be added to the applicability of this AD. The thrust reverser 
accumulator is an optional installation for STC SA944NW. The current 
STC holder did not purchase the thrust reverser data, and the thrust 
reverser accumulators cannot be installed without using the STCs 
identified in this AD. Furthermore, deleting reference to STCs 
SA1731SW, SA1669SW, and SA1670SW would expand the applicability of this 
AD, creating further delay in addressing the unsafe condition. If we 
become aware of affected thrust reverser accumulators equipped on other 
Learjet Model 23, 24, 24A, 24B, 24B-A, 24D, 24D-A, 24E, 24F, 25, 25A, 
25B, 25C, 25D, and 25F airplanes, we will consider further rulemaking.
    Operators should note that on August 12, 2005 we issued an NPRM, 
Docket No. FAA-2005-22169 (70 FR 49210, August 23, 2005), related to 
the unsafe condition of this AD. The related NPRM proposes to require 
replacement of the spherical accumulator for the main hydraulic system 
with a new cylindrical accumulator. The related NPRM is applicable to 
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. The spherical 
accumulator used for the main airplane hydraulic system on those 
Learjet model airplanes is similar to the spherical accumulator used 
for the thrust reverser hydraulic system addressed in this AD. The 
actions proposed in the related NPRM are intended 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.

Request To Include Final Action

    One commenter recommends adding information about the final action 
being developed under FAA project ST8103SC-T. The commenter states that 
referencing the proposed STC number would provide information to 
operators about the final action.
    We do not agree. As stated in an earlier comment, we may consider 
additional rulemaking once a modification is developed, approved, and 
available. Therefore no change to this AD is necessary in this regard.

Request To Eliminate Repetitive Inspections of the Thrust Reverser

    One commenter requests that we eliminate repetitive inspections of 
the thrust reverser (at intervals of 300 and 600 flight hours). The 
commenter suggests these inspections are unnecessary if a thrust 
reverser is deactivated.
    We do not agree because this AD and the referenced service bulletin 
do not require repetitive inspections of the thrust reverser. We infer 
that the commenter is referring to the repetitive inspections of the 
thrust reversers specified in The Nordam Group TR3000 Service Manual 
DHP-G-25-1. These repetitive inspections are part of the maintenance 
program for STCs SA1731SW, SA1669SW, and SA1670SW. After making the 
thrust reverser accumulator inoperable, operators should do repetitive 
general visual inspections of the thrust reverser system for cracking, 
corrosion, loose or missing fasteners, etc., to ensure the structural 
integrity of the thrust reverser. (The Nordam Group has issued 
Temporary Revision 78-04, dated July 8, 2005, to the TR3000 Service 
Manual to add these new repetitive inspections.) Operational checks 
should no longer be done after the thrust reverser accumulator is 
inoperable. Operators may contact the Manager, Special Certification 
Office, ASW-190, Rotorcraft Directorate, for the revised maintenance 
inspection program. No change to this AD is necessary in this regard.

Change to This AD

    In paragraph (c) of the NPRM, we inadvertently omitted the word 
``accumulators'' where the applicability identifies the part numbers of 
the affected thrust reverser accumulators. We have added 
``accumulators'' before the affected part numbers in paragraph (c) of 
this AD to clarify the applicability.

Clarification of Alternative Method of Compliance (AMOC) Paragraph

    We have revised this action to clarify the appropriate procedure 
for notifying the principal inspector before using any approved AMOC on 
any airplane to which the AMOC applies.

Conclusion

    We have carefully reviewed the available data, including the 
comments received, and determined that air safety and the public 
interest require adopting the AD with the changes described previously. 
We have determined that this change will neither increase the economic 
burden on any operator nor increase the scope of the AD.

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 AD affects about 255 airplanes of U.S. registry. 
The actions in this AD 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 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 AD will not have federalism 
implications under

[[Page 69061]]

Executive Order 13132. This AD will 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 this AD:
    (1) Is not a ``significant regulatory action'' under Executive 
Order 12866;
    (2) Is not a ``significant rule'' under 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 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, Incorporation by 
reference, Safety.

Adoption of the Amendment

0
Accordingly, under the authority delegated to me by the Administrator, 
the FAA amends 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

0
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]

0
2. The Federal Aviation Administration (FAA) amends Sec.  39.13 by 
adding the following new airworthiness directive (AD):

2005-23-06 Learjet: Amendment 39-14364. Docket No. FAA-2005-20947; 
Directorate Identifier 2004-NM-245-AD.

Effective Date

    (a) This AD becomes effective December 19, 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 reverser accumulators having 
part number (P/N) 25-0570-127-1, -3, -7, -13, or -17.

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)(1) 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.
    (2) Before using any AMOC approved in accordance with 14 CFR 
39.19 on any airplane to which the AMOC applies, notify the 
appropriate principal inspector in the FAA Flight Standards 
Certificate Holding District Office.

Material Incorporated by Reference

    (i) You must use The Nordam Group Alert Service Bulletin A3000 
78-21, dated November 25, 2002, to perform the actions that are 
required by this AD, unless the AD specifies otherwise. The Director 
of the Federal Register approved the incorporation by reference of 
this document in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. 
Contact The Nordam Group, Nacelle/Thrust Reverser Systems Division, 
6911 North Whirlpool Drive, Tulsa, Oklahoma 74117, for a copy of 
this service information. You may review copies at the Docket 
Management Facility, U.S. Department of Transportation, 400 Seventh 
Street, SW., room PL-401, Nassif Building, Washington, DC; on the 
Internet at http://dms.dot.gov; or at the National Archives and 
Records Administration (NARA). For information on the availability 
of this material at the NARA, call (202) 741-6030, or go to http://www.archives.gov/federal-register/cfr/ibr-locations.html.

    Issued in Renton, Washington on October 28, 2005.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 05-22215 Filed 11-10-05; 8:45 am]
BILLING CODE 4910-13-P

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