[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

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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

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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