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, 49210-49212 [05-16752]

Download as PDF 49210 Federal Register / Vol. 70, No. 162 / Tuesday, August 23, 2005 / Proposed Rules actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. 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 Impact The regulations proposed herein 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. Therefore, it is determined that this proposal would not have federalism implications under Executive Order 13132. For the reasons discussed above, I certify that this 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) if promulgated, 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. A copy of the draft regulatory evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting the Rules Docket at the location provided under the caption ADDRESSES. List of Subjects in 14 CFR Part 39 Air transportation, Aircraft, Aviation safety, Safety. The Proposed Amendment Accordingly, pursuant to the authority delegated to me by the VerDate jul<14>2003 16:15 Aug 22, 2005 Jkt 205001 Administrator, the Federal Aviation Administration proposes to amend part 39 of the Federal Aviation Regulations (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. § 39.13 [Amended] 2. Section 39.13 is amended by adding the following new airworthiness directive: Alternative Methods of Compliance (c) The Manager, Seattle 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. Issued in Renton, Washington, on August 12, 2005. Ali Bahrami, Manager, Transport Airplane Directorate, Aircraft Certification Service. [FR Doc. 05–16751 Filed 8–22–05; 8:45 am] BILLING CODE 4910–13–P DEPARTMENT OF TRANSPORTATION Boeing: Docket 2001–NM–213–AD. Applicability: All Model 747SP, 747SR, 747–100, –100B, –100B SUD, –200B, –200C, –200F, and –300 series airplanes; certificated in any category. Compliance: Required as indicated, unless accomplished previously. To prevent improper deployment of the escape slide/raft or blockage of the passenger/crew doors in the event of an emergency evacuation, which could result in injury to passengers or crewmembers, accomplish the following: Modification (a) Within 36 months after the effective date of this AD: Accomplish the actions specified in paragraphs (a)(1) and (a)(2) of this AD, as applicable, in accordance with Boeing Special Attention Service Bulletin 747–25–3274, Revision 3, dated December 16, 2004. Previously accomplishing the modification in accordance with Boeing Special Attention Service Bulletin 747–25– 3274, Revision 1, dated January 9, 2003; or Revision 2, dated August 26, 2004; is acceptable for compliance with paragraph (a)(1) of this AD, except as specified in paragraph 1.D, ‘Description’, of Revision 3 of the service bulletin. (1) For airplanes on which the actions specified in Boeing Service Bulletin 747–25– 2666, Revision 2, dated April 24, 2003; and Goodrich Service Bulletin 25–238, Revision 1, dated January 31, 2003, have been accomplished: Replace cable assemblies having part number (P/N) 69B55462–( ) with new cable assemblies having P/N 416U6004– 1. (2) For airplanes on which the modification required by paragraph (a)(1) of this AD has not been accomplished: Modify the escape slide/raft pack assembly (includes removing the slide packs, replacing the cover release pin cable assemblies with new assemblies, and removing the cable guard bracket, as applicable). Concurrent Modification (b) For Groups 2, 5, 6, 7, 8, 11, 12, 13, 14, and 15 airplanes: Prior to or concurrently with accomplishment of paragraph (a) of this AD, modify the outboard cover panel of the cable release sliders of the floor-mounted upper deck slide pack assembly, as specified in Figure 2 of Boeing Special Attention Service Bulletin 747–25–3307, Revision 2, dated July 8, 2004. PO 00000 Frm 00011 Fmt 4702 Sfmt 4702 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 Federal Aviation Administration (FAA), Department of Transportation (DOT). ACTION: Notice of proposed rulemaking (NPRM). AGENCY: 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. E:\FR\FM\23AUP1.SGM 23AUP1 Federal Register / Vol. 70, No. 162 / Tuesday, August 23, 2005 / Proposed Rules Use one of the following addresses to submit comments on this proposed AD. • DOT Docket Web site: Go to https://dms.dot.gov and follow the instructions for sending your comments electronically. • Government-wide rulemaking Web site: Go to https://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 https:// 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: ADDRESSES: 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 https:// 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. VerDate jul<14>2003 16:15 Aug 22, 2005 Jkt 205001 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 https:// dms.dot.gov. Examining the Docket You can examine the AD docket on the Internet at https://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 PO 00000 Frm 00012 Fmt 4702 Sfmt 4702 49211 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 E:\FR\FM\23AUP1.SGM 23AUP1 49212 Federal Register / Vol. 70, No. 162 / Tuesday, August 23, 2005 / Proposed Rules 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. 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. 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. List of Subjects in 14 CFR Part 39 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 VerDate jul<14>2003 16:15 Aug 22, 2005 Jkt 205001 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. § 39.13 [Amended] 2. The FAA amends § 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 PO 00000 Frm 00013 Fmt 4702 Sfmt 4702 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 E:\FR\FM\23AUP1.SGM 23AUP1

Agencies

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


-----------------------------------------------------------------------

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).

-----------------------------------------------------------------------

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 https://dms.dot.gov and follow 
the instructions for sending your comments electronically.
     Government-wide rulemaking Web site: Go to https://
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 
https://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 https://
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 https://dms.dot.gov.

Examining the Docket

    You can examine the AD docket on the Internet at https://
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

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