Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 94-NM-198-AD]

Airworthiness Directives; Boeing Model 737-300, -400, and -500

Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness

directive (AD) that is applicable to certain Boeing Model 737-300, -

400, and -500 series airplanes. This proposal would require replacement

of the horizontal stabilizer trim electric actuator. This proposal is

prompted by reports of a binding condition in the clutch disk in the

horizontal stabilizer trim electric actuator. The actions specified by

the proposed AD are intended to prevent reduced controllability of the

airplane due to binding of a clutch disk in the horizontal stabilizer

trim electric actuator.

DATES: Comments must be received by January 19, 1995.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

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

Attention: Rules Docket No. 94-NM-198-AD, 1601 Lind Avenue, SW.,

Renton, Washington 98055-4056. Comments may be inspected at this

location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except

Federal holidays.

The service information referenced in the proposed rule may be

obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle,

Washington 98124-2207. This information may be examined at the FAA,

Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton,

Washington.

FOR FURTHER INFORMATION CONTACT: Kenneth W. Frey, Aerospace Engineer,

Systems and Equipment Branch, ANM-132S, FAA, Transport Airplane

Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue,

SW., Renton, Washington 98055-4056; telephone (206) 227-2673; fax (206)

227-1181.

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-198-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-198-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

Recently, the FAA has received reports from operators of Boeing

Model 737-300, -400, and -500 series airplanes that the stabilizer trim

wheel continued to turn after the switches for the stabilizer trim had

been operated and released. Investigation revealed that the clutch disk

in the horizontal stabilizer trim electric actuator may have caused the

clutch to bind intermittently.

Normally, when the switches for the stabilizer trim are operated,

the horizontal stabilizer trim electric actuator turns and engages

either the ``nose up'' or the ``nose down'' clutch, which causes the

stabilizer to move. When the switches for the stabilizer trim are

released, the clutch disengages, and the actuator continues to turn

until it stops (coasts) through deceleration. Under normal operating

conditions, the stabilizer movement stops immediately after the clutch

disengages.

However, a binding clutch may cause the stabilizer to continue to

move while the electric actuator coasts. The stabilizer may move in the

direction it was last commanded or it may reverse and move in the

opposite direction. The direction depends on which clutch disk is

binding. This condition, if not corrected, could result in reduced

controllability of the airplane.

The FAA has reviewed and approved Boeing Alert Service Bulletin

737-27A1191, Revision 1, dated November 3, 1994, which describes

procedures for replacement of horizontal stabilizer trim electric

actuators, having part number (P/N) 10-62033-3, with a different model

(P/N 10-62033-4) that eliminates the problems associated with binding

of the clutch disk.

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 require replacement of the electric actuator of the

stabilizer trim with a different model. The actions would be required

to be accomplished in accordance with the alert service bulletin

described previously.

[Note: 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. Under these circumstances, at least one operator appears to

have incorrectly assumed that its airplane was not subject to an AD.

On the contrary, 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 requirement.]

There are approximately 1,448 Model 737-300, -400, and -500 series

airplanes of the affected design in the worldwide fleet. The FAA

estimates that 590 airplanes of U.S. registry would be affected by this

proposed AD, that it would take approximately 4 work hours per airplane

to accomplish the proposed actions, and that the average labor rate is

$60 per work hour. The cost of required parts would be approximately

$600 per airplane. Based on these figures, the total cost impact of the

proposed AD on U.S. operators is estimated to be $495,600, or $840 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 adding the following new

airworthiness directive:

Boeing: Docket 94-NM-198-AD.

Applicability: Model 737-300, -400, and -500 series airplanes;

as listed in Boeing Alert Service Bulletin 737-27A1191, Revision 1,

dated November 3, 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 (c) to request approval from the FAA. This

approval may address either no action, if the current configuration

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 reduced controllability of the airplane, accomplish

the following:

(a) Within 12 months after the effective date of this AD,

replace the horizontal stabilizer trim electric actuator having part

number 10-62033-3 with one that has been modified and re-identified

as P/N 10-62033-4, in accordance with Boeing Alert Service Bulletin

737-27A1191, Revision 1, dated November 3, 1994.

(b) As of the effective date of this AD, no person shall install

a horizontal stabilizer trim electric actuator having part number

10-62033-3 on any airplane.

(c) 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, Seattle 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, Seattle ACO.

Note 2: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the Seattle ACO.

(d) 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.

Issued in Renton, Washington, on November 16, 1994.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-28745 Filed 11-21-94; 8:45 am]

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