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

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]

BILLING CODE 4910-13-U