[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]
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