[Federal Register Volume 61, Number 193 (Thursday, October 3, 1996)]
[Proposed Rules]
[Pages 51624-51625]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-25307]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-67-AD]
RIN 2120-AA64


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 replacing 
certain aileron/rudder trim control modules with a new module that 
contains an improved rudder trim switch to reduce internal friction. 
This proposal is prompted by reports of sticking conditions in the 
rudder trim switch. The actions specified by the proposed AD are 
intended to prevent such sticking, which could result in uncommanded 
movement of the rudder and consequent deviation of the airplane from 
its set course.

DATES: Comments must be received by November 12, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-67-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: Hania Younis, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington; 
telephone (206) 227-2764; 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 96-NM-67-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. 96-NM-67-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received reports of sticking conditions in the rudder 
trim switch on electric aileron/rudder trim control module P8-43 on 
certain Model 737 series airplanes. One such report involved an 
airplane that was climbing, under manual control, through an altitude 
of 6,700 feet. The airplane began to yaw slightly to the left and the 
flight crew felt some force on the rudder pedals; although the rudder 
trim switch knob was centered, the rudder trim indicator showed that 
the rudder was set at an angle of 16 degrees left of where it was 
supposed to be.
    If the trim switch sticks, it may be prevented from returning to 
the center position. If this happens, the rudder trim actuator may 
continue to move the rudder at a slow rate, up to the trim limit. This 
rate of movement is very slow, however, at approximately 1/2 deg. per 
second, which should provide ample time for the flight crew to detect 
and correct the movement before it creates a situation of concern. In 
most cases, these types of incidents can be stopped if the pilot merely 
puts the switch into the center position

[[Page 51625]]

manually. In all incidents of this type, the rudder movement can by 
stopped by use of the rudder pedals within the normal limits for yaw 
control.
    Sticking conditions in the rudder trim switch if not corrected, 
however, could result in uncommanded movement of the rudder, and 
consequent deviation of the airplane from its set course.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
737-27A1198, dated June 6, 1996, which describes procedures for 
replacing aileron/rudder trim control module P8-43 with a new module 
that contains an improved switch. This improved module minimizes 
internal friction that has caused the sticking conditions.

Explanation of Requirements of Proposed Rule

    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 replacing the aileron/rudder trim control 
module P8-43 with a new improved module. The actions would be required 
to be accomplished in accordance with the alert service bulletin 
described previously.

Cost Impact

    There are approximately 1,159 Boeing Model 737-300, -400, and -500 
series airplanes of the affected design in the worldwide fleet. The FAA 
estimates that 537 airplanes of U.S. registry would be affected by this 
proposed AD. Replacement of the module would take approximately 3 work 
hours per airplane to accomplish, at an average labor rate of $60 per 
work hour. Required parts would cost approximately $1,063 per airplane. 
Based on these figures, the cost impact of the proposed AD on U.S. 
operators is estimated to be $667,491, or $1,243 per airplane.
    The 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.

Regulatory Impact

    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. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

Boeing: Docket 96-NM-67-AD.

    Applicability: Model 737-300, -400, and -500 series airplanes; 
as listed in Boeing Alert Service Bulletin 737-27A1198, dated June 
6, 1996; certified in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
otherwise 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 request approval for an 
alternative method of compliance in accordance with paragraph (b) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.
    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent sticking conditions in the rudder trim switch, which 
could result in uncommanded movement of the rudder and consequent 
deviation of the airplane from its set course, accomplish the 
following:
    (a) Within 2 years after the effective date of this AD, replace 
the aileron/rudder trim control module P8-43 having part number (P/
N) 69-73703-5 or 69-73703-6 with a new aileron/rudder trim control 
module having P/N 69-73703-8, in accordance with Boeing Alert 
Service Bulletin 737-27A1198, dated June 6, 1996.
    (b) 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.
    (c) 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 September 26, 1996.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-25307 Filed 10-2-96; 8:45 am]
BILLING CODE 4910-13-U