[Federal Register Volume 63, Number 63 (Thursday, April 2, 1998)]
[Rules and Regulations]
[Pages 16091-16094]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-8352]


-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 95-NM-207-AD; Amendment 39-10436; AD 98-07-16]
RIN 2120-AA64


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to certain Boeing Model 737-300, -400, and -500 series 
airplanes, that requires interchanging the location of the hydraulic 
fuse and the flow limiter of the standby hydraulic system of the 
leading edge. This amendment also requires replacing the existing 
hydraulic fuses in the standby hydraulic system with new fuses. This 
amendment 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 in extreme cold environment, can adversely affect the operation 
of the fuse. The actions specified by this AD are intended to

[[Page 16092]]

prevent such adversely affected operation of the fuse, which could 
result in the loss of all standby hydraulic system pressure and 
consequent severely reduced controllability of the airplane during 
certain flight phases.

DATES: Effective May 7, 1998.
    The incorporation by reference of certain publications, as listed 
in the regulations, is approved by the Director of the Federal Register 
as of May 7, 1998.

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: Kenneth W. Frey, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-
4056; telephone (425) 227-2673; fax (425) 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 
January 7, 1997 (62 FR 947). That action proposed to 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. That action 
also proposed to require replacing the existing hydraulic fuses in the 
standby hydraulic system with new fuses that are not affected by low 
temperature operation.
    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

    One commenter supports the proposed rule.

Requests to Revise the Compliance Times of the Proposed Interchange 
and Replacement Actions

    The Air Transport Association (ATA) of America states that one 
commenter generally supports the proposed action; however, this 
commenter requests an amended compliance time of 18 months in lieu of 
4,000 flight hours specified in paragraph (b) of the proposed AD. The 
commenter states that such an extension is needed because of an 
expected large demand for these fuses. A second commenter requests 
changing the compliance time to 6,000 flight hours or 2 years, 
whichever occurs first, because the hydraulic fuse manufacturer is 
unable to support a compliance time of 4,000 flight hours. Another 
commenter also requests a change in the compliance time to 6,000 flight 
hours.
    The FAA concurs partially with these requests and acknowledges that 
parts availability and scheduling may present problems. The FAA does 
not concur with the request to extend the compliance time from 4,000 
flight hours to 6,000 flight hours, or the request to change it to 
6,000 flight hours or 2 years, whichever occurs first. However, the FAA 
has considered the need to allow additional time to obtain the number 
of fuses required for the fleet and to avoid scheduling problems for 
the replacement of discrepant fuses. Therefore, the FAA has revised 
paragraph (b) of the final rule to read: ``Within 18 months or 4,000 
flight hours after the effective date of this AD, whichever occurs 
later. . . .'' In addition, for the same reasons, the FAA has revised 
the compliance time of paragraph (a) of the final rule, which is 
identical to paragraph (b). The FAA has determined that extending these 
compliance times will not adversely affect safety.

Requests to Clarify the Summary Section of the Preamble

    Two commenters request a number of revisions and additions to 
clarify the technical content of the ``Summary'' Section of the NPRM.
    In that section, one commenter requests that the third sentence be 
changed from ``* * * and excessive fusing volumes of some of the fuses, 
can adversely affect * * * '' to ``* * * and excessive fusing volumes 
of some of the fuses in extreme cold environment, can adversely affect 
* * *.'' The FAA concurs with this request and has changed the final 
rule accordingly.
    Two commenters request that the statement of unsafe condition be 
changed from ``* * * in the loss of all hydraulic system pressure and 
consequent severely reduced controllability of the airplane'' to ``* * 
* in the loss of all standby hydraulic system pressure and may reduce 
the controllability of the airplane during certain flight phases.'' The 
FAA concurs partially with these changes. The FAA has determined that 
the word ``standby'' and the phrase ``during certain flight phases'' 
add clarity and has revised the final rule accordingly. However, the 
FAA does not concur with the proposed addition of ``may reduce the 
controllability'' to the sentence, because the FAA considers that 
``could result in'' is more accurate.

Requests to Clarify Additional Sections of the Preamble

    1. ``Discussion'' Section. In the first paragraph of this section, 
one commenter requests that the second sentence be changed from 
``Results of that performance test * * *'' to ``In the existing 
configuration, the standby leading edge flow limiter is upstream of the 
standby leading edge fuse. The results of the performance test revealed 
that this configuration of the flow limiter and fuse assembly adversely 
affects the operation of the fuse.''
    In the second paragraph of this section, one commenter requests 
deleting the second sentence and changing the third sentence from ``* * 
* are not affected by this condition * * *'' to ``* * * are not 
affected by this condition because steady state temperatures keep the 
fluid warm.''
    In the third paragraph of this section, two commenters request 
changing the second sentence from ``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 * * *'' to ``Hydraulic 
fuses are designed to prevent total loss of the hydraulics system after 
a certain volume of fluid (continually/continuously) passes through the 
fuse following the development of a leak downstream of the fuse.''
    2. Explanation of Relevant Service Information. In the second 
paragraph of this section, two commenters request changing the first 
sentence from ``* * * new fuses that are not affected by low 
temperature operation'' to ``* * * new fuses that function in low 
temperatures.'' These commenters also request changing the second 
sentence from ``* * * as a result of fluid depletion if a leak occurs 
downstream of the fuses'' to ``* * * as a result of a fuse failing to 
set following a leak downstream of the fuses.''
    3. Explanation of Requirements of Proposed Rule. In the first 
paragraph of this section, two commenters request changing the second 
sentence from ``* * * new fuses that are not affected by low 
temperature operation'' to ``* * * new fuses that function at/in low 
temperatures.''

[[Page 16093]]

    Although the FAA acknowledges that the commenters' suggested 
wording in these sections of the preamble adds technical clarity, the 
FAA has determined that these changes are not relevant because these 
sections do not appear in the final rule.

Requests to Clarify the Body of the AD

    One commenter requests changing paragraph (b) to read: ``For 
airplanes listed in Boeing Service Bulletin 737-29-1071 (line numbers 
2001 through 2791). * * *'' The FAA does not concur with this request 
for two reasons. First, the line number ``2001'' is incorrect, and the 
correct number (1001) is shown in the applicability of the proposed AD. 
Second, because the line numbers are included in the applicability of 
the AD, it is unnecessary to include them elsewhere in the AD.
    Two commenters request changing paragraph (b) to read ``* * * with 
new fuses that are not adversely affected during low temperature 
operation. * * *'' The FAA has determined that this change adds clarity 
and has changed the wording of the final rule accordingly.

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 with the changes previously 
described. The FAA has determined that these changes will neither 
increase the economic burden on any operator nor increase the scope of 
the AD.

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 will be affected by this 
AD.
    The FAA estimates that it will take approximately 2 work hours per 
airplane to accomplish the required 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 will be minimal. Based on these 
figures, the cost impact of the required interchange on U.S. operators 
is estimated to be $71,520, or $120 per airplane.
    The FAA also estimates that it will take approximately 4 work hours 
per airplane to accomplish the required replacement, at an average 
labor rate of $60 per work hour. Required parts will be provided by the 
manufacturer at no cost to operators. Based on these figures, the cost 
impact of the required 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 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:

98-07-16 Boeing: Amendment 39-10436. 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 
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 standby hydraulic system pressure and 
consequent severely reduced controllability of the airplane during 
certain flight phases, accomplish the following:
    (a) For airplanes listed in Boeing Service Bulletin 737-29-1070, 
dated June 8, 1995: Within 18 months or 4,000 flight hours after the 
effective date of this AD, whichever occurs later, 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 18 months or 4,000 flight hours after the 
effective date of this AD, whichever occurs later, replace the 
existing hydraulic fuses in the standby hydraulic system with new 
fuses that are not adversely affected during 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.
    (e) The actions shall be done in accordance with Boeing Service 
Bulletin 737-29-1070, dated June 8, 1995, and Boeing Service 
Bulletin 737-29-1071, dated May 16, 1996. This incorporation by 
reference was approved by the Director of the Federal Register in 
accordance with 5 U.S.C. 552(a)

[[Page 16094]]

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.
    (f) This amendment becomes effective on May 7, 1998.

    Issued in Renton, Washington, on March 25, 1998.
Darrell M. Pederson,
Acting Manager,
Transport Airplane Directorate,
Aircraft Certification Service.
[FR Doc. 98-8352 Filed 4-1-98; 8:45 am]
BILLING CODE 4910-13-U