[Federal Register Volume 62, Number 4 (Tuesday, January 7, 1997)]
[Proposed Rules]
[Pages 947-949]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-253]
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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39
[Docket No. 95-NM-207-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
interchanging the location of the hydraulic fuse and the flow limiter
of the standby hydraulic system of the leading edge. The proposed AD
also would require replacing the existing hydraulic fuses in the
standby hydraulic system with new fuses. This proposal is prompted by
reports of a performance test of the hydraulic fuses, which revealed
that the positioning of the flow limiter in the existing configuration,
and excessive fusing volumes of some of the fuses, can adversely affect
the operation of the fuse. The actions specified by the proposed AD are
intended to prevent such adversely affected operation of the fuse,
which could result in the loss of all hydraulic system pressure and
consequent severely reduced controllability of the airplane.
DATES: Comments must be received by February 18, 1997.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), Transport Airplane Directorate, ANM-103,
Attention: Rules Docket No. 95-NM-207-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
[[Page 948]]
Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington.
FOR FURTHER INFORMATION CONTACT: Kenneth W. Frey, Aerospace Engineer,
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft
Certification Office, 1601 Lind Avenue, SW., Renton, Washington;
telephone (206) 227-2673; 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 95-NM-207-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. 95-NM-207-AD, 1601 Lind Avenue, SW., Renton, Washington
98055-4056.
Discussion
The FAA received a report indicating that a performance test of the
fuses in the hydraulic systems of certain Boeing Model 737 series
airplanes was conducted. Results of that performance test revealed
that, in the existing configuration, the flow limiter of the standby
hydraulic system of the leading edge is positioned upstream of the
hydraulic fuse. Such positioning of the flow limiter can adversely
affect the operation of the fuse.
The FAA also received a report indicating that certain fuses
installed in the standby hydraulic system exceed specified ``fusing
volumes'' (the fluid volume allowed to pass through the fuse before it
shuts off) at low hydraulic fluid temperatures. This condition also can
adversely affect the operation of the fuse. The fuses in hydraulic
systems A and B are not affected by this condition. However, the fuses
in the standby hydraulic system are affected, since they are exposed to
low temperatures because of the intermittent operation of the standby
system.
The standby hydraulic system provides a backup system after the
pressure of either (or both) the A or B hydraulic system drops below a
minimum pressure setting. The hydraulic fuse is designed to prevent
total loss of the hydraulics systems after a certain volume of fluid
passes through the fuse within a specified time following the
development of a leak downstream of the fuse. The hydraulic fuse also
allows part of the hydraulic system to remain pressurized if such a
leak develops. If the A and B hydraulic systems fail, and the standby
hydraulic system develops a leak downstream of a failed fuse, the
airplane could lose all hydraulic system pressure. This condition, if
not corrected, could result in severely reduced controllability of the
airplane.
Explanation of Relevant Service Information
The FAA has reviewed and approved Boeing Service Bulletin 737-29-
1070, dated June 8, 1995, which describes procedures for interchanging
the location of the hydraulic fuse and the flow limiter of the standby
hydraulic system of the leading edge so that the hydraulic fuse is
positioned upstream of the flow limiter. Accomplishment of this action
will ensure normal operation of the hydraulic fuse.
The FAA also has reviewed and approved Boeing Service Bulletin 737-
29-1071, dated May 16, 1996, which describes procedures for replacing
the existing hydraulic fuses in the standby hydraulic system with new
fuses that are not affected by low temperature operation. Installation
of these new fuses will prevent the possible loss of the standby
hydraulic system as a result of fluid depletion if a leak occurs
downstream of the fuses.
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 interchanging the location of the hydraulic
fuse and the flow limiter of the standby hydraulic system of the
leading edge so that the hydraulic fuse is positioned upstream of the
flow limiter. The proposed AD also would require replacing the existing
hydraulic fuses in the standby hydraulic system with new fuses that are
not affected by low temperature operation. The actions would be
required to be accomplished in accordance with the service bulletins
described previously.
Cost Impact
There are approximately 1,791 Boeing Model 737-300, -400, and -500
series airplanes of the affected design in the worldwide fleet. The FAA
estimates that 596 airplanes of U.S. registry would be affected by this
proposed AD.
The FAA estimates that it would take approximately 2 work hours per
airplane to accomplish the proposed interchange of the hydraulic fuse
and the flow limiter, and that the average labor rate is $60 per work
hour. The cost for required parts would be minimal. Based on these
figures, the cost impact of the proposed interchange on U.S. operators
is estimated to be $71,520, or $120 per airplane.
The FAA also estimates that it would take approximately 4 work
hours per airplane to accomplish the proposed replacement, at an
average labor rate of $60 per work hour. Required parts would be
provided by the manufacturer at no cost to operators. Based on these
figures, the cost impact of the proposed replacement on U.S. operators
is estimated to be $143,040, or $240 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
[[Page 949]]
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 95-NM-207-AD.
Applicability: Model 737-300, -400, and -500 series airplanes
having line numbers 1001 through 2791, inclusive; 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 adversely affected operation of the fuse, which could
result in the loss of all hydraulic system pressure and consequent
severely reduced controllability of the airplane, accomplish the
following:
(a) For airplanes listed in Boeing Service Bulletin 737-29-1070,
dated June 8, 1995: Within 4,000 flight hours after the effective
date of this AD, interchange the location of the hydraulic fuse and
the flow limiter of the standby hydraulic system of the leading edge
so that the hydraulic fuse is positioned upstream of the flow
limiter, in accordance with Boeing Service Bulletin 737-29-1070,
dated June 8, 1995.
(b) For airplanes listed in Boeing Service Bulletin 737-29-1071,
dated May 16, 1996: Within 4,000 flight hours after the effective
date of this AD, replace the existing hydraulic fuses in the standby
hydraulic system with new fuses that are not affected by low
temperature operation, in accordance with Boeing Service Bulletin
737-29-1071, dated May 16, 1996.
(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 December 31, 1996.
S.R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 97-253 Filed 1-6-97; 8:45 am]
BILLING CODE 4910-13-U
