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

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 94-NM-210-AD; Amendment 39-9097; AD 94-26-01]

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: Final rule; request for comments.

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SUMMARY: This amendment adopts a new airworthiness directive (AD) that

is applicable to certain Learjet Model 24, 25, 31, 35, 36, and 55

series airplanes, and Learjet Model 28 and 29 airplanes. This action

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. This action also provides optional terminating action for

that AFM revision. This amendment is prompted by a report of failure of

a safety valve in the pressurization system on a Learjet Model 31A

airplane and reports of cracks found in the poppets of certain outflow/

safety valves due to an improper molding process. The actions specified

in this AD are intended to prevent such cracking and subsequent failure

of the valves, which could result in rapid decompression of the

airplane.

DATES: Effective January 3, 1995.

The incorporation by reference of certain publications listed in

the regulations is approved by the Director of the Federal Register as

of January 3, 1995.

Comments for inclusion in the Rules Docket must be received on or

before February 14, 1995.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Transport Airplane Directorate, ANM-103,

Attention: Rules Docket No. 94-NM-210-AD, 1601 Lind Avenue SW., Renton,

Washington 98055-4056.

FOR FURTHER INFORMATION CONTACT: Walter Eierman, Aerospace Engineer,

Systems and Equipment Branch, ANM-131L, 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: Recently, the FAA received 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. These conditions, if not corrected, could

result in rapid decompression of the airplane.

The FAA has reviewed and approved Allied Signal Aerospace Alert

Service Bulletins 130406-21-A4011, Revision 2, dated September 28,

1994, and 102850-21-A4021, Revision 2, dated October 6, 1994. These

alert service bulletins describe procedures for replacement of certain

outflow/safety valves in the 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 an unsafe condition has been identified that is likely to

exist or develop on other products of the same type design, this AD is

being issued to prevent rapid decompression of the airplane. This AD

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. This AD also provides for replacement of certain outflow/

safety valves in the pressurization system as optional terminating

action for the AFM revision.

This is considered to be interim action. The FAA is considering

further rulemaking action to supersede this AD to require replacement

of certain outflow/safety valves within 18 months. However, the

proposed compliance time for the replacement is sufficiently long so

that notice and time for public comment would not be impracticable.

Since a situation exists that requires the immediate adoption of

this regulation, it is found that notice and opportunity for prior

public comment hereon are impracticable, and that good cause exists for

making this amendment effective in less than 30 days.

Comments Invited

Although this action is in the form of a final rule that involves

requirements affecting flight safety and, thus, was not preceded by

notice and an opportunity for public comment, comments are invited on

this rule. Interested persons are invited to comment on this 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 under the caption ADDRESSES. All

communications received on or before the closing date for comments will

be considered, and this rule may be amended in light of the comments

received. Factual information that supports the commenter's ideas and

suggestions is extremely helpful in evaluating the effectiveness of the

AD action and determining whether additional rulemaking action would be

needed.

Comments are specifically invited on the overall regulatory,

economic, environmental, and energy aspects of the rule that might

suggest a need to modify the 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 that

summarizes each FAA-public contact concerned with the substance of this

AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments

submitted in response to this rule must submit a self-addressed,

stamped postcard on which the following statement is made: ``Comments

to Docket Number 94-NM-210-AD.'' The postcard will be date stamped and

returned to the commenter.

The regulations adopted herein will 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 final

rule does not have sufficient federalism implications to warrant the

preparation of a Federalism Assessment.

The FAA has determined that this regulation is an emergency

regulation that must be issued immediately to correct an unsafe

condition in aircraft, and that it is not a ``significant regulatory

action'' under Executive Order 12866. It has been determined further

that this action involves an emergency regulation under DOT Regulatory

Policies and Procedures (44 FR 11034, February 26, 1979). If it is

determined that this emergency regulation otherwise would be

significant under DOT Regulatory Policies and Procedures, a final

regulatory evaluation will be prepared and placed in the Rules Docket.

A copy of it, if filed, may be obtained from the Rules Docket at the

location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by

reference, Safety.

Adoption of the Amendment

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration amends 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 adding the following new

airworthiness directive:

94-26-01 Learjet: Amendment 39-9097. Docket 94-NM-210-AD.

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 2, dated September 28, 1994; or 102850-21-A4021,

Revision 2, dated October 6, 1994; certificated in any category.

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 the effective date of this AD, 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) Replacement of outflow/safety valves, part numbers 130406-1

and 102850-5, as identified in Allied Signal Aerospace Alert Service

Bulletin 130406-21-A4011, Revision 2, dated September 28, 1994, or

102850-21-A4021, Revision 2, dated October 6, 1994, as applicable;

with a serviceable part in accordance with the procedures described

in the applicable alert service bulletin; constitutes terminating

action for the AFM limitation required by paragraph (a) of this AD.

Following such replacement, that AFM limitation may be removed from

the AFM.

(c) As of the effective date of this AD, 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 2, dated September 28, 1994, 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

Operations Inspector, who may add comments and then send it to the

Manager, Los Angeles ACO.

Note: 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

Secs. 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.

(f) The replacement shall be done in accordance with Allied

Signal Aerospace Alert Service Bulletin 130406-21-A4011, Revision 2,

dated September 28, 1994; or Allied Signal Aerospace Alert Service

Bulletin 102850-21-A4021, Revision 2, dated October 6, 1994; as

applicable. This incorporation by reference was approved by the

Director of the Federal Register in accordance with 5 U.S.C. 552(a)

and 1 CFR part 51. Copies may be obtained from Allied Signal, Inc.,

Controls & Accessories, 11100 N. Oracle Road, Tucson, Arizona 85737-

9588; telephone (602) 469-1000. Copies may be inspected 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; or at the Office of the Federal Register, 800

North Capitol Street, NW., suite 700, Washington, DC.

(g) This amendment becomes effective on January 3, 1995.

Issued in Renton, Washington, on December 9, 1994.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-30801 Filed 12-15-94; 8:45 am]

BILLING CODE 4910-13-U