[Federal Register Volume 61, Number 168 (Wednesday, August 28, 1996)]
[Proposed Rules]
[Pages 44247-44249]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-21885]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-153-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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[[Page 44248]]

SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 737 series 
airplanes. This proposal would require modification of the aileron 
center spring and trim mechanism. This proposal is prompted by a review 
of the design of the flight control systems on Model 737 series 
airplanes. The actions specified by the proposed AD are intended to 
prevent jamming of the aileron control system during flight due to 
fracturing of the springs in the aileron centering units; this 
condition, if not corrected, could result in reduced lateral control of 
the airplane.

DATES: Comments must be received by October 24, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-153-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: Don Kurle, Senior Engineer, Systems 
and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification 
Office, 1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-
2798; 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-153-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-153-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    In October 1994, the FAA organized a team to conduct a Critical 
Design Review (CDR) of the flight control systems installed on Boeing 
Model 737 series airplanes in an effort to confirm the continued 
operational safety of these airplanes. The formation of the CDR team 
was prompted by questions that arose following an accident involving a 
Model 737-200 series airplane that occurred near Colorado Springs, 
Colorado, and one involving a Model 737-300 series airplane that 
occurred near Pittsburgh, Pennsylvania. The CDR team's analysis of the 
flight control systems was performed independent of the investigations 
of these accidents, which are conducted by the National Transportation 
Safety Board (NTSB). The cause of the accidents has not yet been 
determined.
    The CDR team was composed of representatives from the FAA, the 
NTSB, other U.S. government organizations, and foreign airworthiness 
authorities. The team reviewed the service history and the design of 
the flight control systems of Model 737 series airplanes. The team 
completed its review in May 1995. The recommendations of the team 
include various changes to the design of the flight control systems of 
these airplanes, as well as correction of certain design deficiencies. 
This proposed AD is one of nine rulemaking actions being issued by the 
FAA to address the recommendations of the CDR team.

Reports Received by FAA

    The FAA received numerous reports indicating that fractured springs 
were found in the aileron centering units on Model 737 series 
airplanes. The cause of the fracturing has been attributed to fatigue 
cracking. A fractured spring can result in degraded aileron feel at the 
control wheel. Two of these reports indicated that a fractured spring 
became lodged in a centering cam weight reduction hole when the control 
wheel was turned beyond 40 degrees. This condition, if not corrected, 
could result in jamming of the aileron control system; jamming of the 
aileron control system during flight could result in reduced lateral 
control of the airplane.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Bulletin 737-27-
1155, dated October 26, 1989; as revised by Notices of Status Change 
No. 737-27-1155NSC1, dated January 25, 1990, No. 737-27-1155NSC2, dated 
February 15, 1990, and No. 737-27-1155NSC3, dated May 17, 1990; which 
describe procedures for modification of the aileron center spring and 
trim mechanism. The modification involves the following:

--for Groups 1 and 2 airplanes, replacing the aileron centering springs 
with improved springs that are corrosion resistant and more durable;
--for Groups 1 and 2 airplanes, plugging a weight reduction hole in the 
feel cam to prevent foreign materials from lodging in the mechanism; 
and
--for Group 1 airplanes only, replacing the eyebolts of the centering 
spring attachment with new eyebolts that have extended arms to prevent 
a fractured centering spring from lodging in or behind the feel cam.

    Accomplishment of these actions will improve the reliability of the 
aileron centering spring and trim mechanism.

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 modification of the aileron center spring and 
trim mechanism. The actions would be required to be accomplished in 
accordance with the service bulletin and Notice of Status Change 
described previously.

Explanation of Proposed Compliance Time

    In developing an appropriate compliance time for the proposed 
modification, the FAA's intent is that it be performed during a 
regularly scheduled maintenance visit for the majority of the affected 
fleet, when the airplanes would be located at a base where special 
equipment and trained personnel would be readily available, if 
necessary. In addition, the FAA

[[Page 44249]]

considered the availability of necessary parts. The FAA finds that 18 
months corresponds closely to the interval representative of most of 
the affected operators' normal maintenance schedules. The FAA considers 
that this interval will provide an acceptable level of safety.

Cost Impact

    There are approximately 1,631 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 830 
airplanes of U.S. registry would be affected by this proposed AD.
    The FAA estimates that 485 Group 1 airplanes would be affected by 
this proposed AD. For Group 1 airplanes, the FAA estimates that it 
would take approximately 2 work hours per airplane to accomplish the 
proposed actions, and that the average labor rate is $60 per work hour. 
Required parts would cost approximately $707 per airplane. Based on 
these figures, the cost impact of the proposed AD on U.S. operators of 
Group 1 airplanes is estimated to be $401,095, or $827 per airplane.
    The FAA estimates that 345 Group 2 airplanes would be affected by 
this proposed AD. For Group 2 airplanes, the FAA estimates that it 
would take approximately 2 work hours per airplane to accomplish the 
proposed actions, and that the average labor rate is $60 per work hour. 
Required parts would cost approximately $224 per airplane. Based on 
these figures, the cost impact of the proposed AD on U.S. operators of 
Group 2 airplanes is estimated to be $118,680, or $344 per airplane.
    The cost impact figures discussed above are 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-153-AD.

    Applicability: Model 737 series airplanes; as listed in Boeing 
Service Bulletin 737-27-1155, dated October 26, 1989; as revised by 
Notices of Status Change No. 737-27-1155NSC1, dated January 25, 
1990, No. 737-27-1155NSC2, dated February 15, 1990, and No. 737-27-
1155NSC3, dated May 17, 1990; 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 (c) 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 jamming of the aileron control system during flight, 
which could result in reduced lateral control of the airplane, 
accomplish the following:
    (a) Within 18 months after the effective date of this AD, 
accomplish the requirements of paragraphs (a)(1), (a)(2), and (a)(3) 
of this AD, as applicable, in accordance with Boeing Service 
Bulletin 737-27-1155, dated October 26, 1989; as revised by Notice 
of Status Change No. 737-27-1155NSC1, dated January 25, 1990, and 
Notice of Status Change No. 737-27-1155NSC2, dated February 15, 
1990, and Notice of Status Change No. 737-27-1155NSC3, dated May 17, 
1990.
    (1) For Groups 1 and 2 airplanes: Replace the aileron centering 
springs, part number (P/N) 69-39429-2, with improved springs, P/N 
69-39429-3, in accordance with the service bulletin and Notices of 
Status Change.
    (2) For Groups 1 and 2 airplanes: Install a two-piece plug, P/N 
69-78072-1, in the weight reduction hole in the feel cam in 
accordance with the service bulletin and Notices of Status Change.
    (3) For Group 1 airplanes: Replace the two eyebolts, P/N 69-
39423-1, of the aileron centering spring attachment with new 
eyebolts, P/N 69-74646-1, in accordance with the service bulletin 
and Notices of Status Change.
    (b) As of the effective date of this AD, no person shall install 
the items specified in paragraphs (b)(1) and (b)(2) of this AD on 
any airplane, as specified:
    (1) For Groups 1 and 2 airplanes: Aileron centering springs 
having P/N 69-39429-2 shall not be installed.
    (2) For Group 1 airplanes: Eyebolts, P/N 69-39423-1, of the 
aileron centering spring attachment shall not be installed.
    (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 
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 August 21, 1996.
Ronald T. Wojnar,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-21885 Filed 8-23-96; 9:03 am]
BILLING CODE 4910-13-U