[Federal Register Volume 65, Number 54 (Monday, March 20, 2000)]
[Rules and Regulations]
[Pages 14834-14838]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-6491]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-58-AD; Amendment 39-11639; AD 2000-05-29]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, 
and -500 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to certain Boeing Model 737-100, -200, -300, -400, and -500 
series airplanes, that requires repetitive inspections to detect 
cracking of various areas of the forward pressure bulkhead, and repair, 
if necessary. This amendment also provides for certain optional 
preventive modifications, which, if accomplished, would terminate the 
repetitive inspections for the affected areas. This amendment is 
prompted by reports indicating that numerous fatigue cracks were found 
on critical areas of the forward pressure bulkhead. The actions 
specified by this AD are intended to prevent such fatigue cracking, 
which could result in rapid decompression of the airplane fuselage.

DATES: Effective April 24, 2000.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of April 24, 2000.

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: Nenita K. Odesa, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle 
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2557; 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 737-100, -
200, -300, -400, and -500 series airplanes was published in the Federal 
Register on October 9, 1998 (63 FR 54391). That action proposed to 
require repetitive inspections to detect cracking of various areas of 
the forward pressure bulkhead, and repair, if necessary. That action 
also proposed to require certain preventive modifications, which, when 
accomplished, would terminate the repetitive inspections for most, but 
not all, of the affected areas.

Comments

    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

    Two commenters support the proposed rule.

Request to Increase the Initial Inspection Threshold

    Several commenters, including the manufacturer, request an increase 
in the initial inspection threshold from 15,000 total flight cycles, as 
proposed, to 20,000 total flight cycles, as recommended in Boeing Alert 
Service Bulletin 737-57A1173, Revision 2, dated January 15, 1998. The 
commenters state that research by the manufacturer supports the 
conclusion that the compliance threshold recommended in the alert 
service bulletin is adequate. To justify its request, the manufacturer 
submitted substantiating data that show that the compliance time 
recommended in the service bulletin is conservative.
    The FAA concurs with the commenters' requests to revise the initial 
compliance threshold in the final rule to match the compliance time 
recommended by the manufacturer in the alert service bulletin (i.e., 
prior to the accumulation of 20,000 total flight cycles or within 3,000 
flight cycles after the effective date of this AD, whichever occurs 
later). After review of the data submitted by the manufacturer, the FAA 
has determined that the compliance times recommended in the alert 
service bulletin are adequate to ensure that any cracks will be 
detected before the cracks reach critical length. Therefore, paragraph 
(a) of this final rule has been revised accordingly, and paragraphs 
(a)(1) and (a)(2) have not been included in this final rule.

Request to Use Repetitive Inspection Interval Specified in Alert 
Service Bulletin

    Most of the commenters request that the repetitive inspection 
interval be revised to more closely correspond with those recommended 
in Boeing Alert Service Bulletin 737-57A1173, Revision 2. Several of 
the commenters justify their requests by stating that, because of the 
difficulty in accessing the affected area, accomplishing the proposed 
inspections outside of a regularly scheduled ``C''-check would place a 
significant burden on operators. The commenters also provide various 
other justifications for their requests, including:
     The compliance times specified in the alert service 
bulletin are conservative.
     Operators are already performing the inspections specified 
in the service bulletin, so there is a significant amount of data on 
cracking in the affected area.
     No in-flight incidents (including loss of pressurization) 
have been reported related to the cracking addressed in the proposal.
     Cracks in the affected area of the forward pressure 
bulkhead propagate very slowly.

[[Page 14835]]

    A number of commenters also provide substantial amounts of data to 
support their requests.
    The FAA concurs with the commenters' requests to require the 
repetitive inspections at the interval recommended in the alert service 
bulletin. Based on the FAA's review of the analyses submitted by the 
manufacturer to substantiate the repetitive inspection intervals 
recommended in the alert service bulletin, the FAA has determined that 
a repetitive inspection interval of 6,000 flight cycles is adequate to 
ensure that any cracking will be detected and corrected in a timely 
manner. Paragraph (a) of this final rule has been revised accordingly.

Request to Address Existing Repairs

    Two commenters request that the proposal be revised to address 
repairs on the affected areas of the forward pressure bulkhead. 
Paragraph (b) of the proposal states that repairs are to be 
accomplished ``in accordance with the Accomplishment Instructions of 
Boeing Alert Service Bulletin 737-53A1173, Revision 2, dated January 
15, 1998; except, where the alert service bulletin specifies that the 
manufacturer may be contacted for repair instructions,. . .'' repairs 
should be accomplished in accordance with a method approved by the FAA. 
One commenter also inquires whether repairs in accordance with the 
Structural Repair Manual (SRM) (which is approved by the FAA) that are 
not referenced in Boeing Alert Service Bulletin 737-53A1173, Revision 
2, or other repairs that are approved by the FAA, will need further 
approval.
    The FAA concurs with the request to address repairs that are 
accomplished in accordance with the SRM but are not referenced in the 
alert service bulletin. Since the issuance of the notice of proposed 
rulemaking (NPRM), the FAA has reviewed and approved Boeing Alert 
Service Bulletin 737-53A1173, Revision 3, dated May 6, 1999. Among 
other things, Revision 3 of the alert service bulletin includes 
references to new chapters of the SRM as acceptable sources of service 
information for the accomplishment of repairs. In addition, since the 
issuance of the NPRM, the FAA also has determined that SRM chapters 
referenced in Boeing Service Bulletin 737-53A1173, Revision 1, dated 
April 25, 1996, are acceptable sources of service information for 
accomplishment of repairs. Therefore, paragraph (b) of this final rule 
has been revised to add references to Boeing Service Bulletin 737-
53A1173, Revision 1, and Boeing Alert Service Bulletin 737-53A1173, 
Revision 3, as acceptable sources of information for accomplishment of 
repairs, except where the service bulletin specifies that the 
manufacturer may be contacted for repair instructions.
    Another commenter requests that the proposal be revised to approve 
repairs accomplished in accordance with data approved by a Designated 
Engineering Representative (DER) but not in accordance with the SRM.
    The FAA concurs that repairs not in accordance with the SRM but 
approved by a DER are acceptable for compliance with this AD. However, 
the FAA has determined that DER-approved repairs are acceptable methods 
of compliance to the AD only if the responsible DER has been authorized 
by the FAA to make such a finding. For all other repairs (i.e., repairs 
not accomplished in accordance with a method approved by the FAA, or in 
accordance with data meeting the type certification basis of the 
airplane approved by a Boeing Company Designated Engineering 
Representative who has been authorized by the FAA to make such a 
finding) that affect the performance of the requirements of this AD, 
the owner/operator must request approval for an alternative method of 
compliance in accordance with paragraph (d) of this AD. Therefore, 
paragraph (b) of the final rule has been revised to state that repairs 
accomplished in accordance with a method approved by the FAA, or in 
accordance with data meeting the type certification basis of the 
airplane approved by a Boeing Company Designated Engineering 
Representative who has been authorized by the FAA to make such 
findings, are acceptable for compliance with this AD.
    In addition, one commenter, the airplane manufacturer, inquires 
whether Boeing DER's have the authority to approve Boeing Service 
Bulletin 737-53A1208, and Boeing Alert Service Bulletin 73757A1173, 
Revision 3. The commenter also inquires whether Boeing DER's will be 
authorized to approve alternative methods of compliance to the AD when 
allowed by law. The commenter makes no specific request for a change to 
the AD.
    With regard to DER approval of the referenced service bulletins, as 
stated previously, since receipt of the comment, the FAA has reviewed 
and approved Boeing Service Bulletin 737-53A1208, and Boeing Service 
Bulletin 737-57A1173, Revision 3. With regard to DER approval of 
alternative methods of compliance, the FAA is considering authorizing 
certain Boeing DER's to approve alternative methods of compliance that 
provide an acceptable level of safety. After this AD has been issued, 
designated DER's will receive a letter from the FAA defining the limits 
of their approval authority. No change to the final rule is necessary 
in this regard.

Request to Revise Number of Affected Airplanes

    One commenter questions how the FAA arrived at its estimate that 
there are 2,802 affected airplanes in the worldwide fleet, as stated in 
the proposal. The commenter points out that the effectivity of Boeing 
Alert Service Bulletin 737-57A1173, Revision 2, includes Boeing Model 
737-100, -200, -200C, -300, -400, and -500 series airplanes having line 
numbers before 2738. The commenter states that 157 of these affected 
airplanes are out of service; therefore, the actual number of affected 
airplanes should be 2,580 airplanes. The commenter makes no specific 
request related to its comment.
    The FAA infers that the commenter is requesting that the proposed 
rule be revised to reduce the estimated number of affected airplanes in 
the worldwide fleet, such that the estimated number of affected 
airplanes is based on airplanes having line numbers 1 through 2737, as 
defined in the alert service bulletin. The FAA concurs with such a 
reduction, and the cost impact section of the preamble of this final 
rule has been revised accordingly.
    In addition, as a result of this comment, the FAA finds that some 
clarification of the applicability of this AD may be necessary. 
Therefore, the applicability statement of this final rule has been 
revised to specifically reference the line numbers of the affected 
airplanes--i.e., line numbers 1 through 2737 inclusive--rather than the 
service bulletin in which the affected airplanes are listed. (This 
change makes no additional airplanes subject to this AD.)

Request to Use Alternative Repetitive Inspection Interval

    Two commenters suggest repetitive inspection intervals other than 
those specified in the NPRM or the alert service bulletin. One 
commenter recommends that the FAA require repetitive visual inspections 
at intervals not to exceed 4,500 flight cycles, and repetitive high 
frequency eddy current inspections at intervals not to exceed 12,000 
cycles. Another commenter's recommendation involves scheduling the 
repetitive inspections based on the number of total flight cycles 
accrued.
    The FAA does not concur with the commenters' suggestions for an 
alternative repetitive inspection threshold. The FAA finds that to 
require

[[Page 14836]]

only visual inspections at intervals not to exceed 4,500 flight cycles, 
and high frequency eddy current inspections at intervals not to exceed 
12,000 cycles, may not ensure that cracking will be detected in a 
timely manner. Regarding the request to schedule the repetitive 
inspections based on the number of total flight cycles accrued, the 
commenter submitted no technical data to substantiate its request. No 
change to the final rule is necessary in this regard.

Request to Eliminate Requirement for Preventive Modifications

    One commenter requests that the proposal be revised to eliminate 
the requirement to accomplish the preventive modifications of the 
center web, vertical chords, and side chord areas of the forward 
pressure bulkhead. The commenter justifies its request on the basis 
that Boeing is monitoring the occurrences of cracking of the forward 
pressure bulkhead in the fleet of affected airplanes.
    The FAA does not concur with the commenter's rationale for 
eliminating the preventive modification requirement. The proposal to 
mandate the preventive modifications is based on the FAA's 
determination that long-term continued operational safety will be 
better assured by modifications or design changes to remove the source 
of the problem, rather than by repetitive inspections.
    However, since the issuance of the NPRM, the FAA has determined 
that the preventive modification of the center web specified in Boeing 
Alert Service Bulletin 737-53A1173, Revision 2 [which paragraph (c) of 
the NPRM cites as the appropriate source of service information for the 
preventive modifications], is not adequate to ensure the prevention of 
cracking in the center web area.
    As stated previously, the FAA has reviewed and approved Boeing 
Alert Service Bulletin 737-57A1173, Revision 3. The FAA has determined 
that accomplishment of the preventive modifications of the forward 
pressure bulkhead in accordance with Revision 3 of the alert service 
bulletin is adequate to ensure prevention of cracking and would 
eliminate the need for the repetitive inspections. However, because 
additional work would be required over that which was proposed in the 
NPRM, mandating the preventive modifications in accordance with 
Revision 3 of the alert service bulletin would require the issuance of 
a supplemental notice of proposed rulemaking to reopen the public 
comment period. The FAA finds that to delay this final rule in this way 
would be inappropriate because the FAA has determined that an unsafe 
condition exists and the required inspections and repairs, if 
necessary, must be accomplished in a timely manner to ensure continued 
safety.
    In addition, the FAA finds that it would be more appropriate to 
provide the option for all preventive modifications to be accomplished, 
at the same time, in accordance with Revision 3 of the alert service 
bulletin, rather than to require only the modification of the vertical 
chords and side chords at WL 195 in accordance with Revision 2 of the 
alert service bulletin. Therefore, paragraph (c) of this final rule has 
been revised to remove the requirement to accomplish any of the 
preventive modifications, and to provide for accomplishment of the 
preventive modifications in accordance with Revision 3 of the alert 
service bulletin as an option that would constitute terminating action 
for the repetitive inspection requirements of this AD. The FAA also may 
consider further rulemaking to require accomplishment of the preventive 
modifications in accordance with Revision 3 of the alert service 
bulletin.

Request for Clarification of Language

    One commenter notes that, in several locations, the NPRM refers to 
an ``unsafe condition.'' The commenter inquires what is meant by 
``unsafe,'' and how such a determination was made by the FAA. The 
commenter makes no specific request for a change.
    The FAA infers that the commenter is requesting clarification of 
language used in the NPRM. The FAA defines an unsafe condition as one 
that could result in a hazardous condition. As stated in the preamble 
of the NPRM, the FAA has received reports indicating that operators 
have found numerous fatigue cracks on the body station 178 forward 
pressure bulkhead on certain Boeing Model 737 series airplanes. Because 
fatigue cracks were found in certain critical structural areas of the 
bulkhead, the FAA finds that such fatigue cracking constitutes an 
unsafe condition, in that it could result in rapid decompression of the 
airplane fuselage. No change to the final rule is necessary in this 
regard.
    The same commenter inquires what is meant by the phrases ``degree 
of urgency associated with the unsafe condition,'' and ``average 
utilization of the affected fleet,'' which appear in the ``Differences 
Between Proposed Rule and Alert Service Bulletin'' section of the NPRM. 
With regard to ``degree of urgency,'' the commenter inquires how this 
degree was determined and considered in the NPRM. The commenter 
questions what events have occurred since 1994 (i.e., when the largest 
reported bulkhead crack was found and the initial issue of Boeing 
Service Bulletin 737-53A1173 was issued) that lend a ``degree of 
urgency'' to the proposed rulemaking. With regard to ``average 
utilization of the affected fleet,'' the commenter questions how 
average utilization was considered in the proposed rulemaking.
    The FAA infers from the context in which the phrases were used 
(specifically, in explaining why the proposed compliance time was 
reduced from the compliance time recommended in the service bulletin) 
that the commenter is requesting clarification as to what events or 
specific factors prompted the FAA to propose a compliance time of 
15,000 total flight cycles and a repetitive interval of 3,000 flight 
cycles for the repetitive inspections proposed in the NPRM.
    The degree of urgency associated with the unsafe condition was 
determined and considered based on the nature of the cracking. A 25-
inch crack in the web of the forward pressure bulkhead prompted the 
issuance of the original service bulletin in 1994. In 1997, the FAA 
received reports of cracking in a new area--the side chord at WL 207. 
Upon review of the history of cracking in the forward pressure 
bulkhead, the FAA determined that cracks had been found in the multiple 
locations on the web, in the vertical beam chords, and in the side 
chords at WL 195 and 207. This determination prompted the FAA to 
consider further rulemaking action, which resulted in the issuance of 
the subject NPRM.
    The FAA evaluated the average utilization of the fleet based on a 
review of the average annual cycles of affected airplanes. Such annual 
utilization numbers and the ``C''-check maintenance interval 
(approximately 12 to 18 months) of several operators of the affected 
airplanes were considered in developing the compliance times.
    However, considering the context in which the subject phrases 
appeared, the FAA finds that the commenter's inquiries on both degree 
of urgency and average utilization of the fleet are no longer relevant 
to the final rule. As stated previously, this final rule has been 
revised to specify the same compliance times recommended by the 
manufacturer in Revisions 2 and 3 of the service bulletin. The FAA 
finds that no further change to the final rule is necessary in this 
regard.

Request to Consider Additional Rulemaking

    One commenter, the airplane manufacturer, states that it is

[[Page 14837]]

considering issuing a separate service bulletin to address fatigue 
cracking in Boeing Model 737 series airplanes having line numbers 2738 
through 3071 inclusive. The commenter inquires whether the FAA is 
considering rulemaking activity for that service bulletin, but makes no 
specific request related to its comment.
    Since receipt of the comment, Boeing has issued Service Bulletin 
737-53A1208, dated May 6, 1999, which specifies inspections and 
modifications to address fatigue cracking in Boeing Model 737 series 
airplanes having line number 2738 through 3071 inclusive. The FAA may 
consider further rulemaking action to mandate the inspections and 
modifications defined in the service bulletin. No change to the final 
rule is necessary in this regard.

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 described 
previously. 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 2,580 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 1,130 airplanes of U.S. 
registry will be affected by this AD.
    It will take approximately 380 work hours per airplane to 
accomplish the required inspections, at an average labor rate of $60 
per work hour. Based on these figures, the cost impact of the 
inspections required by this AD on U.S. operators is estimated to be 
$25,764,000, or $22,800 per airplane, per inspection cycle.
    The cost impact figure discussed above is 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:

2000-05-29 Boeing: Amendment 39-11639. Docket 98-NM-58-AD.

    Applicability: Model 737-100, -200, -300, -400, and -500 series 
airplanes; having line numbers 1 through 2737 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 (d) 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 detect fatigue cracking of the forward pressure bulkhead, 
which could result in rapid decompression of the airplane fuselage, 
accomplish the following:

Initial and Repetitive Inspections

    (a) Prior to the accumulation of 20,000 total flight cycles, or 
within 3,000 flight cycles after the effective date of this AD, 
whichever occurs later, perform inspections of the center web, 
vertical chords, and side chord areas of the forward pressure 
bulkhead for fatigue cracking, in accordance with the Accomplishment 
Instructions of Boeing Alert Service Bulletin 737-53A1173, Revision 
2, dated January 15, 1998, or Revision 3, dated May 6, 1999. 
Thereafter, repeat the inspections at intervals not to exceed 6,000 
flight cycles until the preventive modifications specified by 
paragraph (c) of this AD have been accomplished.

Repairs

    (b) If any crack is found during any inspection required by 
paragraph (a) of this AD, prior to further flight, repair the area 
in accordance with the Accomplishment Instructions of Boeing Service 
Bulletin 737-53A1173, Revision 1, dated April 25, 1996, or Boeing 
Alert Service Bulletin 737-53A1173, Revision 2, dated January 15, 
1998, or Revision 3, dated May 6, 1999; in accordance with a method 
approved by the Manager, Seattle Aircraft Certification Office 
(ACO), FAA, Transport Airplane Directorate; or in accordance with 
data meeting the type certification basis of the airplane approved 
by a Boeing Company Designated Engineering Representative who has 
been authorized by the Manager, Seattle ACO, to make such findings; 
except, where the alert service bulletin specifies that the 
manufacturer may be contacted for repair instructions, repair in 
accordance with a method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA, Transport Airplane Directorate.

Optional Terminating Action

    (c) Accomplishment of the preventive modifications of the center 
web, vertical chords, and side chord areas, including the side chord 
areas at water line 207, of the forward pressure bulkhead, in 
accordance with Boeing Alert Service Bulletin 737-53A1173, Revision 
3, dated May 6, 1999, constitutes terminating action for the 
repetitive inspections requirements of paragraph (a) of this AD for 
that area.

    Note 2: Accomplishment of the preventive modification of the 
vertical chords and side chord areas at water line 195 in accordance 
with Boeing Alert Service Bulletin 737-53A1173, Revision 2, 
constitutes terminating action for the repetitive inspections 
requirements of paragraph (a) of this AD for the vertical chords and 
side chord at WL 195 only.

Alternative Methods of Compliance

    (d) 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 ACO. 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.



[[Page 14838]]


    Note 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permits

    (e) Special flight permits may be issued in accordance with 
Secs. 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.

Incorporation by Reference

    (f) The inspections shall be done in accordance with Boeing 
Alert Service Bulletin 737-53A1173, Revision 2, dated January 15, 
1998, or Boeing Alert Service Bulletin 737-53A1173, Revision 3, 
dated May 6, 1999. Except as provided by paragraph (b) of this AD, 
repairs shall be accomplished in accordance with Boeing Service 
Bulletin 737-53-1173, Revision 1, dated April 25, 1996, or Boeing 
Alert Service Bulletin 737-53A1173, Revision 2, dated January 15, 
1998, or Boeing Alert Service Bulletin 737-53A1173, Revision 3, 
dated May 6, 1999. The preventive modifications, if accomplished, 
shall be done in accordance with Boeing Alert Service Bulletin 737-
53A1173, Revision 3, dated May 6, 1999. This incorporation by 
reference was approved by the Director of the Federal Register in 
accordance with 5 U.S.C. 552(a) 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.
    (g) This amendment becomes effective on April 24, 2000.

    Issued in Renton, Washington, on March 10, 2000.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 00-6491 Filed 3-17-00; 8:45 am]
BILLING CODE 4910-13-P