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

[Federal Register Volume 62, Number 52 (Tuesday, March 18, 1997)]
[Rules and Regulations]
[Pages 12739-12740]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-6541]



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Federal Register / Vol. 62, No. 52 / Tuesday, March 18, 1997 / Rules 
and Regulations

[[Page 12739]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 96-NM-67-AD; Amendment 39-9966; AD 97-06-09]
RIN 2120-AA64


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to certain Boeing Model 737-300, -400, and -500 series 
airplanes. This AD requires replacing certain aileron/rudder trim 
control modules with an improved module that contains an improved 
rudder trim switch that precludes the problems of sticking associated 
with the existing switch. This amendment is prompted by reports of 
sticking conditions in the rudder trim switch. The actions specified by 
this 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: Effective April 21, 1997.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of April 21, 1997.

ADDRESSES: The service information referenced in this AD may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the Federal 
Aviation Administration (FAA), Transport Airplane Directorate, Rules 
Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of 
the Federal Register, 800 North Capitol Street, NW., suite 700, 
Washington, DC.

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: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to include an airworthiness 
directive (AD) that is applicable to certain Boeing Model 737-300, -
400, and -500 series airplanes was published in the Federal Register on 
October 3, 1996 (61 FR 51624). That action proposed to require 
replacing the aileron/rudder trim control module P8-43 with an improved 
module that precludes the problems associated with sticking that were 
identified in the existing module.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.

Support for the Proposal

    Two commenters support the proposed AD.

Request To Clarify Description of Replacement Module

    One commenter requests that the FAA's description of the 
replacement module be revised to make it more specific. This commenter 
points out that the Summary and Discussion sections of the preamble to 
the notice described the replacement module as a ``new model that 
contains an improved rudder trim switch to reduce internal friction.'' 
However, the commenter states that the new module incorporates a switch 
that is of an entirely different design and, therefore, accomplishes 
more than just reduce friction. The new switch is much simpler in 
design and is, therefore, more reliable; the simpler design also 
eliminates multiple causes of sticking that have been identified in the 
existing switch. The commenter suggests that the description of the new 
module include this information.
    The FAA concurs that the commenter's description is more specific. 
The FAA has revised the descriptive language in the appropriate 
portions of this preamble to the final rule to include the commenter's 
suggested wording.

Request to Clarify Description of Unsafe Condition

    This same commenter requests that the FAA's description of the 
unsafe condition, which appeared in the Discussion section of the 
preamble to the notice, be revised. The commenter points to a sentence 
in that section that stated, ``If the trim switch sticks, it may be 
prevented form returning to the center position.'' The commenter states 
that this sentence would be more accurate if stated as ``If the trim 
switch sticks, it may be prevented from returning to the center 
position when the switch knob is released.''
    The FAA does not concur. The FAA does acknowledge that the majority 
of incidents prompting this AD action have involved switches that did 
not return to the center position when the switch knob was released. 
However, according to the manufacturer, it is possible that rudder 
pedals would be required to control rudder movement; i.e., it is 
possible that even returning the switch to the center position manually 
may not be effective. Therefore, the commenter's proposed wording would 
not be accurate for all possible failure scenarios.

Request to Change Proposed Actions Altogether

    One commenter, a non-U.S. operator, requests that the proposal be 
revised by eliminating the proposed actions altogether because they 
will ``only generate additional maintenance costs without affecting 
safety positively.'' Instead, the commenter suggests that the FAA 
propose requiring (1) a clearance check between the rudder trim knob 
and the control panel, and (2) restrictions on food and beverages in 
the cockpit. This commenter maintains that the main cause of rudder 
trim runaways is due to interference between the rudder trim knob and 
the control panel, and, in most cases, this interference is the result 
of dirt (i.e., dust and food) collecting beneath the knob and 
contaminating the switches. In light of this, the commenter considers 
that requiring a gap check and a cleaning task would be a better course 
of action.
    The FAA does not concur. While a gap check and cleaning task would 
be effective in removing contamination once it occurs, the newly 
designed

[[Page 12740]]

module required by this AD will prevent contamination of the switch. 
Therefore, it eliminates the potential for the circumstances prompting 
the unsafe condition from developing, and does not impose additional 
restrictions or cleaning requirements.

Conclusion

    After careful review of the available data, including the comments 
noted above, the FAA has determined that air safety and the public 
interest require the adoption of the rule as proposed.

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 will be affected by this 
AD, that it will take approximately 3 work hours per airplane to 
accomplish the required actions, and that the average labor rate is $60 
per work hour. Required parts will cost approximately $1,063 per 
airplane. Based on these figures, the cost impact of the 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 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 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.
    For the reasons discussed above, I certify that this action (1) is 
not a ``significant regulatory action'' under Executive Order 12866; 
(2) is not a ``significant rule'' under 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. A final evaluation has been prepared for this action 
and it is contained in the Rules Docket. A copy of it 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. 106(g), 40113, 44701.


Sec. 39.13   [Amended]

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

97-06-09 Boeing: Amendment 39-9966. 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; certificated 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.
    (d) The replacement shall be done in accordance with Boeing 
Alert Service Bulletin 737-27A1198, dated June 6, 1996. 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 Boeing Commercial Airplane Group, 
P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be 
inspected at the FAA, Transport Airplane Directorate, 1601 Lind 
Avenue, SW., Renton, Washington; or at the Office of the Federal 
Register, 800 North Capitol Street, NW., suite 700, Washington, DC.
    (e) This amendment becomes effective on April 21, 1997.

    Issued in Renton, Washington, on March 10, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-6541 Filed 3-17-97; 8:45 am]
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