Airworthiness Directives; Learjet Model 24, 25, 31, 35, 36, and 55 Series Airplanes, and Learjet Model 28 and 29 Airplanes

[Federal Register Volume 60, Number 51 (Thursday, March 16, 1995)] [Proposed Rules] [Pages 14231-14233] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 95-6322]

======================================================================== Proposed Rules Federal Register ________________________________________________________________________ This section of the FEDERAL REGISTER contains notices to the public of the proposed issuance of rules and regulations. The purpose of these notices is to give interested persons an opportunity to participate in the rule making prior to the adoption of the final rules. ========================================================================

Federal Register / Vol. 60, No. 51 / Thursday, March 16, 1995 / Proposed Rules [[Page 14231]]

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 94-NM-211-AD]

Airworthiness Directives; Learjet Model 24, 25, 31, 35, 36, and 55 Series Airplanes, and Learjet Model 28 and 29 Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Learjet Model 24, 25, 31, 35, 36, and 55 series airplanes, and Learjet Model 28 and 29 airplanes, that currently requires a revision to the Limitations Section of the FAA-approved Airplane Flight Manual (AFM) to prohibit flight above an altitude of 41,000 feet. The actions specified by that AD are intended to prevent cracking and subsequent failure of the outflow/safety valves, which could result in rapid decompression of the airplane. This action would require replacement of certain outflow/ safety valves, which, when accomplished, constitutes terminating action for the previously required AFM limitation.

DATES: Comments must be received by May 8, 1995.

ADDRESSES: Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-103, Attention: Rules Docket No. 94-NM-211-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9 a.m. and 3 p.m., Monday through Friday, except Federal holidays. The service information referenced in the proposed rule may be obtained from Allied Signal, Inc., Controls & Accessories, 11100 N. Oracle Road, Tucson, Arizona 85737-9588; telephone (602) 469-1000. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Transport Airplane Directorate, Los Angeles Aircraft Certification Office, 3960 Paramount Boulevard, Lakewood, California.

FOR FURTHER INFORMATION CONTACT: Walter Eierman, Aerospace Engineer, Systems and Equipment Branch, ANM-130L, FAA, Transport Airplane Directorate, Los Angeles Aircraft Certification Office, 3960 Paramount Boulevard, Lakewood, California 90712; telephone (310) 627-5336; fax (310) 627-5210.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the proposed rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified above. All communications received on or before the closing date for comments, specified above, will be considered before taking action on the proposed rule. The proposals contained in this notice may be changed in light of the comments received. Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the proposed rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report summarizing each FAA-public contact concerned with the substance of this proposal will be filed in the Rules Docket. Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this notice must submit a self-addressed, stamped postcard on which the following statement is made: ``Comments to Docket Number 94-NM-211-AD.'' The postcard will be date stamped and returned to the commenter.

Availability of NPRMs

Any person may obtain a copy of this NPRM by submitting a request to the FAA, Transport Airplane Directorate, ANM-103, Attention: Rules Docket No. 94-NM-211-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

On December 9, 1994, the FAA issued AD 94-26-01, amendment 39-9097 (59 FR 64844, December 16, 1994), applicable to certain Learjet Model 24, 25, 31, 35, 36, and 55 series airplanes, and Learjet Model 28 and 29 airplanes, to require a revision to the Limitations Section of the FAA-approved Airplane Flight Manual (AFM) to prohibit flight above an altitude of 41,000 feet. That action was prompted originally by a report of failure of a safety valve in the pressurization system on a Learjet Model 31A airplane. Failure of the valve resulted in depressurization of the cabin. Investigation revealed that the poppets of certain outflow/safety valves were cracked. These discrepant valves, including the safety valve installed on the incident airplane, had been manufactured since January 1, 1989. Certain valves manufactured since that date have been found to be susceptible to cracking due to an improper molding process. Cracking in the poppets of the outflow/safety valves in the pressurization system can result in an open valve with an effective flow area of 4.4 square inches; additionally, the valve may close and remain closed. The requirements of that AD are intended to prevent such cracking and subsequent failure of the valves, which could result in rapid decompression of the airplane. When AD 94-26-01 was issued, it contained a provision for optional replacement of certain outflow/safety valves. Accomplishment of the replacement constitutes terminating action for the AFM revision; after the replacement has been accomplished, the previously required AFM limitation may be removed. In the preamble to AD 94-26-01, the FAA indicated that it intended to revise that AD to require the replacement of those outflow/safety valves. This action proposes such a requirement. The FAA previously reviewed and approved Allied Signal Aerospace Alert Service Bulletins 130406-21-A4011, Revision 2, dated September 28, 1994 (for part number 130406-1); and 102850-21-A4021, Revision 2, dated October 6, 1994 (for part number 102850-5). These alert service bulletins describe procedures for replacement of certain outflow/safety valves in the [[Page 14232]] pressurization system with serviceable valves. Further, the alert service bulletins recommend that the maximum altitude for operation of airplanes that may be equipped with these outflow/safety valves be limited to 41,000 feet as an interim measure until the affected valves are replaced. Since the issuance of AD 94-26-01, Allied Signal Aerospace has issued Revision 3 of one of the alert service bulletins described above, Alert Service Bulletin 130406-21-A4011, dated January 5, 1995 (for part number 130406-1). The FAA has reviewed and approved the revised alert service bulletin, which adds certain valve serial numbers to the effectivity list of the alert service bulletin. The FAA has determined that these additional valve serial numbers also are subject to the unsafe condition specified in this AD, and has referenced Revision 3 of the alert service bulletin as the appropriate source of service information for replacement of outflow/safety valves having part number 130406-1. The FAA also has reviewed and approved the following Learjet service bulletins, which reference the Allied Signal Aerospace alert service bulletins described previously as the appropriate sources of service information: 1. SB 24/25-21-4, dated January 3, 1995 (for Model 24 and 25 series airplanes); 2. SB 28/29-21-8, dated January 3, 1995 (for Model 28 and 29 airplanes); 3. SB 31-21-6, dated January 3, 1995 (for Model 31 series airplanes); 4. SB 35/36-21-19, dated January 3, 1995 (for Model 35 and 36 series airplanes); and 5. SB 55-21-10, dated January 3, 1995 (for Model 55 series airplanes). Since an unsafe condition has been identified that is likely to exist or develop on other products of this same type design, the proposed AD would supersede AD 94-26-01 to continue to require a revision to the Limitations Section of the FAA-approved Airplane Flight Manual (AFM) to prohibit flight above an altitude of 41,000 feet. This AD also would require replacement of certain outflow/safety valves. Accomplishment of the replacement constitutes terminating action for the AFM revision; after the replacement has been accomplished, the previously required AFM limitation may be removed. The replacement would be required to be accomplished in accordance with the applicable alert service bulletin described previously. As a result of recent communications with the Air Transport Association (ATA) of America, the FAA has learned that, in general, some operators may misunderstand the legal effect of AD's on airplanes that are identified in the applicability provision of the AD, but that have been altered or repaired in the area addressed by the AD. The FAA points out that all airplanes identified in the applicability provision of an AD are legally subject to the AD. If an airplane has been altered or repaired in the affected area in such a way as to affect compliance with the AD, the owner or operator is required to obtain FAA approval for an alternative method of compliance with the AD, in accordance with the paragraph of each AD that provides for such approvals. A note has been included in this notice to clarify this long-standing requirement. There are approximately 350 Model 24, 25, 31, 35, 36, and 55 series airplanes and Model 28 and 29 airplanes of the affected design in the worldwide fleet. The FAA estimates that 280 airplanes of U.S. registry would be affected by this proposed AD. The AFM revision required currently by AD 94-26-01 takes approximately 1 work hour per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the total cost impact associated with the current AFM revision requirement of AD 94- 26-01 on U.S. operators is estimated to be $16,800, or $60 per airplane. Removal and replacement of parts that would be required by this proposed AD would require approximately 12 work hours to accomplish, at an average labor rate of $60 per work hour. However, Allied Signal advises that it will reimburse operators for the costs of such removal and replacement. Therefore, based on this information, U.S. operators would incur no cost impact for the proposed removal and replacement requirements. Based on the figures discussed above, the (combined) total cost impact of this AD on U.S. operators would be approximately $16,800, or $60 per airplane. The total cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. The regulations proposed herein would not have substantial direct effects 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, in accordance with Executive Order 12612, it is determined that this proposal would not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. 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 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. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by removing amendment 39-9097 (59 FR 64844, December 16, 1994), and by adding a new airworthiness directive (AD), to read as follows:

Learjet: Docket 94-NM-211-AD. Supersedes AD 94-26-01, Amendment 39- 9097.

Applicability: Model 24, 25, 31, 35, 36, and 55 series airplanes, and Model 28 and 29 airplanes; equipped with Allied Signal outflow/safety valves, number 130406-1 or 102850-5; as identified in Allied Signal Aerospace Alert Service Bulletin 130406- 21-A4011, Revision 3, dated January 5, 1995; or 102850-21-A4021, Revision 2, dated October 6, 1994; certificated in any category.

Note 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must use the authority provided in paragraph (d) to request approval from the FAA. This approval may address either no action, if the current configuration [[Page 14233]] eliminates the unsafe condition; or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any airplane from the applicability of this AD.

Compliance: Required as indicated, unless accomplished previously. To prevent rapid decompression of the airplane due to cracking and subsequent failure of certain outflow/safety valves, accomplish the following: (a) Within 30 days after January 3, 1995 (the effective date of AD 94-26-01, amendment 39-9097), revise the Limitations Section of the FAA-approved Airplane Flight Manual (AFM) to include the following. This may be accomplished by inserting a copy of this AD in the AFM. ``Operation of the airplane at any altitude above 41,000 feet is prohibited.'' (b) Within 18 months after the effective date of this AD, replace the outflow/safety valves, part numbers 130406-1 and 102850- 5, as identified in Allied Signal Aerospace Alert Service Bulletin 130406-21-A4011, Revision 3, dated January 5, 1995, or 102850-21- A4021, Revision 2, dated October 6, 1994, as applicable; with serviceable parts in accordance with the procedures described in the applicable alert service bulletin. Accomplishment of this replacement constitutes terminating action for the requirement of paragraph (a) of this AD; after the replacement has been accomplished, the previously required AFM limitation may be removed. (c) As of January 3, 1995 (the effective date of AD 94-26-01, amendment 39-9097), no person shall install an outflow/safety valve, part number 130406-1 or 102850-5, as identified in Allied Signal Aerospace Alert Service Bulletin 130406-21-A4011, Revision 3, dated January 5, 1995, or 102850-21-A4021, Revision 2, dated October 6, 1994, as applicable; on any airplane unless that valve is considered to be serviceable in accordance with the specifications contained in the Accomplishment Instructions of the applicable alert service bulletin. (d) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Los Angeles Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Los Angeles ACO.

Note 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Los Angeles ACO.

(e) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

Issued in Renton, Washington, on March 9, 1995. Neil D. Schalekamp, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service. [FR Doc. 95-6322 Filed 3-15-95; 8:45 am] BILLING CODE 4910-13-U