[Federal Register Volume 67, Number 71 (Friday, April 12, 2002)]
[Rules and Regulations]
[Pages 17917-17923]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-8454]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-196-AD; Amendment 39-12702; AD 2002-07-08]
RIN 2120-AA64


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment supersedes an existing airworthiness directive 
(AD), applicable to certain Boeing Model 737 series airplanes, that 
currently requires repetitive inspections to find cracking of the lower 
skin at the lower row of fasteners in the lap joints of the fuselage, 
and repair of any cracking found. That amendment also requires 
modification of the fuselage lap joints at certain locations, which 
constitutes terminating action for repetitive inspections of the 
modified areas. This amendment adds repetitive inspections and requires 
replacement of the current preventive modification with an improved 
modification. This amendment is prompted by the FAA's determination 
that, in light of additional crack findings, certain modifications of 
the fuselage lap joints do not provide an adequate level of safety. The 
actions specified by this AD are intended to find and fix cracking of 
the fuselage lap joints, which could result in sudden decompression of 
the airplane.

DATES: Effective May 17, 2002.
    The incorporation by reference certain publications, as listed in 
the regulations, is approved by the Director of the Federal Register as 
of May 17, 2002.

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: Scott Fung, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office 
(ACO), 1601 Lind Avenue, SW., Renton, Washington; telephone (425) 227-
1221; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) by superseding AD 97-22-07, 
amendment 39-10179 (62 FR 55732, October 28, 1997), which is applicable 
to certain Boeing Model 737 series airplanes, was published in the 
Federal Register on July 12, 2001 (66 FR 36509). The action proposed to 
continue to require repetitive inspections to find cracking of the 
lower skin at the lower row of fasteners in the lap joints of the 
fuselage, and repair of any cracking found. That action also adds a 
requirement for modification of the fuselage lap joints at certain 
locations, which constitutes terminating action for repetitive 
inspections of the modified areas. That action also adds new repetitive 
inspections and requires replacement of the current preventive 
modification with an improved modification.

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. One commenter supports the intent of the 
proposed rule. Another commenter states that the proposed rule does not 
affect its fleet.

Typographical Error

    One commenter states that in the section titled, ``Other Relevant 
Proposed Rulemaking,'' specified in the proposed rule, the line numbers 
listed for replacement of certain Structural Repair Manual (SRM) 
repairs are line numbers 292 through 2595 inclusive. The commenter 
notes that the correct reference is line numbers 292 through 2565 
inclusive. The FAA agrees that a typographical error was made in that 
section, however, that section is not carried over to the final rule so 
no change is necessary.

Clarify Paragraphs (a) and (g)

    One commenter states that the repetitive low frequency eddy current 
inspections (LFEC) of the crown areas as specified in paragraph (a) of 
the proposed rule need clarification. The commenter notes that the 
crown areas are not defined in the proposed rule and Part 1.E.1. 
(``Compliance'') of Boeing Service Bulletin 737-53A1177, Revision 6, 
dated May 31, 2001 (specified in the proposed rule as the source of 
service information for doing the specified actions), defines the areas 
to be inspected. The commenter adds that the lap joint modification 
(repair) in the crown areas, as specified in paragraph (g) of the 
proposed rule, needs clarification. The commenter notes that the crown 
areas are not defined in the proposed rule and Part 1.E.1. 
(``Compliance'') of the service bulletin defines the areas to be 
inspected.
    The FAA agrees that inclusion of references to Part 1.E.1. 
(``Compliance'') in paragraphs (a) and (g) of this final rule provides 
clarification of the crown lap joint areas to be inspected. We have 
changed paragraphs (a) and (g) of the final rule accordingly.

Credit for Previously Accomplished Modifications

    Two commenters ask that paragraph (g) of the proposed rule be 
changed to include credit for lap joint modifications (repairs) 
accomplished per the instructions described in Boeing Service Bulletin 
737-53A1177, Revision 4, dated September 2, 1999, or Revision 5, dated 
February 15, 2001. One commenter adds that this would terminate the 
post-NACA-modification inspections required by paragraph (i) of the 
proposed rule.
    We agree that accomplishment of the lap joint modification 
(repairs) per Revision 4 or 5 of the referenced service bulletin meets 
the requirements specified in paragraph (g) of the final rule and 
terminates the repetitive post-NACA-modification inspections required 
by paragraph (i) of the final rule, as those revisions are technically 
equivalent to the modification specified in Revision 6 of the service 
bulletin. We have changed paragraph (g) of the final rule accordingly.

Change Paragraph (g)(5)

    One commenter asks that paragraph (g)(5) of the proposed rule, for 
airplanes having a NACA modification per Boeing Alert Service Bulletin 
737-53A1177, Revision 3, dated September 18, 1997, be changed to 
include airplanes that have been modified per Revision 1, dated 
September 19, 1996, or Revision 2, dated July 24, 1997, of that service 
bulletin.
    We agree that airplanes having a NACA modification per Revision 1 
or 2

[[Page 17918]]

of the service bulletin meet the requirements specified in paragraph 
(g)(5) of the final rule. The modification in those revisions is 
technically equivalent to the modification specified in Revision 3 of 
the service bulletin. We have changed paragraph (g)(5) of the final 
rule accordingly.

Clarify Repair Instructions for 737 Cargo Airplanes

    One commenter states that paragraph (g) of the proposed rule does 
not address a certain lap joint repair for Model 737-200C series 
airplanes, Groups 3 and 5, as specified in Revisions 4, 5, and 6 of the 
service bulletin. The commenter notes that Part 1.E.1. (``Compliance'') 
of the service bulletin instructs operators to contact Boeing for 
repair instructions for stringers 4R and 10R. The commenter asks that a 
new paragraph be added with repair instructions for that area.
    We agree and have changed paragraph (g) of the final rule to 
exclude repair per the service bulletin for certain 737-200C series 
airplanes. We also added a new paragraph (h) to this final rule (and 
renumbered subsequent paragraphs) to specify repair instructions for 
stringers 4R and 10R on Groups 3 and 5 airplanes.

Clarify Paragraph (h)

    One commenter states that the repetitive LFEC inspections outside 
the crown areas as specified in paragraph (h) of the proposed rule need 
clarification. The commenter notes that the areas outside the crown lap 
joints are not defined in the proposed rule and Part 1.E.2. 
(``Compliance'') of Boeing Service Bulletin 737-53A1177, Revision 6, 
defines the areas to be inspected. The commenter adds that the 
instructions specified in paragraph (h) of the proposed rule are for 
operators to inspect for cracking at lap joints identified in Figures 2 
through 7 of the referenced service bulletin. The commenter notes that 
Figure 7 addresses inspection of Group 6 airplanes (737-200 and 737-
200C series airplanes, line numbers 1 through 291 inclusive), and those 
airplanes are not subject to the requirements of this AD.
    We agree that inclusion of a reference to Part 1.E.2. 
(``Compliance'') of the service bulletin provides clarification of the 
areas outside the crown lap joints to be inspected. We also agree that 
Group 6 airplanes are not subject to the requirements of this AD and 
have been addressed in another rulemaking action. Therefore, paragraph 
(i) of the final rule (which was paragraph (h) in the proposed rule) 
includes a reference to Part 1.E.2. (``Compliance'') of the service 
bulletin, and includes no reference to Figure 7 of the service 
bulletin.

Clarify Paragraph (i)

    One commenter asks that paragraph (i) of the proposed rule include 
clarification of the areas that require post-accomplishment inspections 
for the NACA modifications in the crown areas as specified in Part 
1.E.4.a. (``Compliance'') of Revision 6 of the service bulletin. The 
commenter also asks that accomplishment of the NACA modification per 
PART III of the Accomplishment Instructions of Boeing Alert Service 
Bulletin 737-53A1177, Revision 1, dated September 19, 1996; Revision 2, 
dated July 24, 1997; or Revision 3, dated September 18, 1997; be 
accepted.
    We agree that inclusion of a reference to Part 1.E.4.a. 
(``Compliance'') of the service bulletin provides clarification of the 
areas in the crown lap joints to be inspected. We also agree that 
inclusion of Revisions 1, 2, and 3 of the service bulletin into 
paragraph (j) of the final rule clarifies the service bulletins that 
can be used to do the NACA modification. Paragraph (j) of the final 
rule (which was paragraph (i) in the proposed rule) includes a 
reference to Part 1.E.4.a. (``Compliance'') of the service bulletin.

Clarify Paragraph (j)

    One commenter asks that paragraph (j) of the proposed rule include 
clarification of the areas that require post-accomplishment inspections 
for the NACA modifications outside the crown areas as specified in Part 
1.E.4.b. (``Compliance'') of Revisions 1, 2, and 3 of the service 
bulletin. The commenter also asks that accomplishment of the NACA 
modification per PART III of the Accomplishment Instructions of Boeing 
Alert Service Bulletin 737-53A1177, Revision 1, dated September 19, 
1996; Revision 2, dated July 24, 1997; or Revision 3, dated September 
18, 1997, be accepted.
    We agree that inclusion of a reference to Part 1.E.4.b. 
(``Compliance'') provides clarification of the areas outside the crown 
lap joints to be inspected. We also agree that inclusion of reference 
to Revisions 1, 2, and 3 of the service bulletin in paragraph (j) of 
the final rule clarifies the service bulletins that can be used to do 
the NACA modification. Paragraph (k) of this final rule (which was 
paragraph (j) in the proposed rule) includes a reference to Part 
1.E.4.b. (``Compliance'') of the service bulletin.

Clarify Paragraph (l)

    One commenter states that paragraph (l) of the proposed rule 
(``Follow-on LFEC Inspections'') should reference Part 1.E.7. 
(``Compliance'') of the referenced service bulletin and should instruct 
operators to do the external inspection per the 737 Nondestructive Test 
(NDT) Manual, Part 6, Chapter 53-30-00, Figure 5.
    We agree that inclusion of a reference to Part 1.E.7. 
(``Compliance'') provides clarification of the area for the external 
inspection as specified in the 737 NDT Manual. However, we do not agree 
to instruct operators to do the external inspection per the 737 NDT 
Manual. Part 1.E.7. (``Compliance'') of the service bulletin references 
the 737 NDT Manual, which addresses the commenter's concerns. Paragraph 
(m) of the final rule (which was paragraph (l) in the proposed rule) 
includes a reference to Part 1.E.7. (``Compliance'') of the service 
bulletin.

Clarify Paragraph (m)

    One commenter asks that paragraph (m) of the proposed rule, 
(``Repetitive High Frequency Eddy Current (HFEC) Inspections--Window 
Corners''), be changed to reference Part 1.E.10. (``Compliance'') of 
the referenced service bulletin to define the procedures necessary for 
inspecting the fuselage skin adjacent to the window corners that have 
not been modified.
    We agree that inclusion of a reference to Part 1.E.10 
(``Compliance'') provides clarification of the inspection procedures 
necessary for doing the HFEC inspections of the window corners. 
Paragraph (n) of the final rule (which was paragraph (m) in the 
proposed rule) includes a reference to Part 1.E.10 (``Compliance'') of 
the service bulletin.
    Another commenter states that the repair and modification 
instructions specified in paragraph (m) of the proposed rule are not 
clear for those operators who have already installed the lap joint 
doublers in the corresponding area of the window belt. The commenter 
adds that, as written, it is unable to determine that the terminating 
modification for uncracked window corners consists of oversizing the 
fastener holes and installing Hi-lok fasteners. The commenter asks for 
further review of the proposed rule given additional circumstances and 
questions from operators who have already met the intent of the 
modification specified in Boeing Service Bulletin 737-53A1177, Revision 
5, dated February 15, 2001.
    We agree that clarification of the repair and modification 
instructions specified in paragraph (m) of the proposed rule is 
necessary. Therefore, we have added that the modification

[[Page 17919]]

includes removing and discarding fasteners, oversizing fastener holes, 
and installing rivets or Hi-Lok fasteners, as applicable. We also agree 
that accomplishment of the modification per Revision 5 of the 
referenced service bulletin meets the requirements for the modification 
specified in paragraph (n) of the final rule. This terminates the 
repetitive inspections for operators who have accomplished the required 
actions per either of those service bulletins. Paragraph (n) of the 
final rule (which was paragraph (m) in the proposed rule) has been 
changed accordingly.

Extend Compliance Time in Paragraph (m)

    One commenter, the airplane manufacturer, asks that the compliance 
time for the initial and repetitive inspections specified in paragraph 
(m) of the proposed rule be extended. The commenter states that the 
1,200-flight-cycle threshold specified is the same inspection threshold 
specified for lap joint lower row cracking in paragraph (a) of the 
proposed rule. The commenter notes that the cracking of the holes of 
the window corner is much less critical than the cracking of the lap 
joint lower row, so it finds a less-restrictive inspection threshold is 
acceptable for the window corner cracking. The commenter adds that 
fleet data on cracking of the holes of the window corner show that such 
cracking is not extensive on airplanes with less than 60,000 total 
flight cycles, and that information supports an inspection threshold of 
2,250 flight cycles after the effective date of the AD for airplanes 
with less than 60,000 total flight cycles.
    We agree with the commenter that the cracking of the window corner 
is less critical than cracking of the lap joint lower row; however, the 
fleet data to date indicate that cracking can occur on airplanes with 
fewer than 50,000 total flight cycles. Therefore, we have changed the 
initial inspection threshold required by paragraph (n) of the final 
rule (which was paragraph (m) in the proposed rule) to read, ``Before 
the accumulation of 50,000 total flight cycles or within 2,250 flight 
cycles after the effective date of this AD, whichever comes later. * * 
*''
    A second commenter suggests an extension of the threshold for the 
inspections to ``Before the accumulation of 60,000 total flight cycles 
or within 5,500 flight cycles after the effective date of the AD, 
whichever occurs later.'' The commenter states that this will allow 
operators that have done the post-modification a reasonable opportunity 
to meet the intent of the new requirement specified in Part V (window 
corner inspection) of Revision 5 or 6 of the referenced service 
bulletin. The commenter adds that its data indicates that the window 
corner cracking is largely due to pressurization cycles. The 
commenter's operations are such that its airframe cycles are of 
relatively low-pressure differential, and very short duration.
    A third commenter asks that the 1,200-flight-cycle threshold be 
elevated to 5,000 flight cycles so that the initial inspection and the 
preventative modification of the window corner on its airplanes can be 
accomplished at the same time as the lap joint modification. The 
commenter states that it has approximately 25 airplanes that are over 
50,000 flight cycles that have not accomplished the window corner 
inspection or lap joint repairs. The commenter adds that a compliance 
interval of 1,200 flight cycles will require the airlines to bring in 
those airplanes for inspection within a 3-month timeframe, without the 
ability to accomplish the preventative modifications.
    The same commenter asks that the compliance time for the initial 
inspection of the window belts be required within 10,000 flight cycles 
after the effective date of the AD, or 20,000 flight cycles after 
accomplishment of the lap joint repairs, whichever occurs first. The 
commenter states that the structural integrity for airplanes on which 
the lap joint repairs have been done has already been improved, which 
justifies changing the compliance time.
    A fourth commenter suggests that the inspection be accomplished 
before the accumulation of 50,000 total flight cycles or within 4,500 
flight cycles after the effective date of the AD, whichever occurs 
later. The commenter states that this will allow operators to schedule 
the inspection into a ``C'' check visit. The commenter adds that, for 
airplanes with 50,000-plus total flight cycles, the 1,200-flight-cycle 
threshold for the initial inspection will place a significant burden on 
operators that have already accomplished the skin lap modifications 
because the inspection will have to be accomplished outside a scheduled 
maintenance visit.
    We do not agree to extend the compliance threshold for the initial 
inspection further, per the above requests from the second, third, and 
fourth commenters. We have already considered factors such as 
operators' maintenance schedules in setting a compliance time for the 
required modification, and have determined that an inspection threshold 
of 2,250 flight cycles is an appropriate compliance time in which the 
inspection may be accomplished during scheduled airplane maintenance 
for the majority of affected operators. Since maintenance schedules 
vary from operator to operator, it would not be possible to guarantee 
that all affected airplanes could be modified during scheduled 
maintenance, even with a compliance threshold of 2,250 flight cycles. 
In any event, we find that this threshold represents the maximum time 
wherein the affected airplanes may continue to operate prior to 
inspection without compromising safety. No further change to the final 
rule is necessary in this regard.

Extend Compliance Time in Paragraph (i)

    One commenter asks that the compliance threshold in paragraph (i) 
of the proposed rule be changed. The commenter states that it has one 
airplane on which the preventative change of the crown lap joint 
stringers has been done, and that airplane will have flown more than 
12,000 flight cycles when this final rule is effective. The commenter 
asks for an alternate initial inspection threshold in paragraph (i) of 
the proposed rule to avoid immediate grounding of that airplane when 
the final rule is issued. The commenter asks that a provision be added 
which states, ``* * * if an airplane has reached the 12,000 flight 
cycle limit, the initial inspection must be done within 6 months or 
1,500 flight cycles, whichever occurs later, after the effective date 
of the AD.''
    We acknowledge the need for operators with airplanes that have 
exceeded the 12,000 flight cycle limit to have ample time to accomplish 
the initial inspection required by paragraph (j) of the final rule 
(which was paragraph (i) in the proposed rule). Paragraph (k) of this 
final rule (which was paragraph (j) in the proposed rule) has a similar 
compliance threshold. Therefore, we have changed paragraphs (j) and (k) 
of this final rule to add a grace period, ``* * * or within 750 flight 
cycles after the effective date of this AD, whichever is later.''

Add Previous Alternative Methods of Compliance (AMOC)

    One commenter asks that paragraph (n) of the proposed rule be 
changed to add a paragraph for previously approved AMOCs for AD 97-22-
07, amendment 39-10179.
    We agree to change paragraph (o) of the final rule (which was 
paragraph (n) in the proposed rule) to add a new paragraph (o)(2) for 
AMOCs previously approved for AD 97-22-07 that are

[[Page 17920]]

approved for certain paragraphs in this AD.

Eliminate References to Bear Strap Areas

    One commenter, the airplane manufacturer, states that, since the 
release of Revision 6 of the referenced service bulletin, its review 
suggests that the cracking of the skin and doublers common to the bear 
strap around the entry and service doors may be caused by hinge 
cutouts, and may not be related to the typical cracking of the lower 
row of the lap splice. The commenter submits this comment for FAA 
review and consideration.
    We infer that the commenter wants to eliminate all references to 
the areas that are common to the bear strap around the entry and 
service doors, as specified in the proposed rule. We do not agree. The 
commenter has not provided substantiating data for its request. We may 
eliminate these areas from the requirements of the final rule in future 
rulemaking if data are submitted showing that cracking in these areas 
is definitely caused by hinge cutouts. No change to the final rule is 
necessary in this regard.

Delete Paragraph (f)

    Two commenters ask that the compliance plan requirement specified 
in paragraph (f) of the proposed rule be deleted.
    One commenter states that the inclusion of paragraph (f) does 
nothing to address the safety issue for which the proposed rule is 
being written, and asks that it be deleted from the final rule. Another 
commenter does not consider the requirements of paragraph (f) an 
airworthiness issue and states that it should not be included as such 
in the final rule. The commenter adds that the letter check does not 
determine if an airplane is airworthy, and the airplanes on which the 
actions required by paragraph (g) of the proposed rule have been done, 
as well as the airplanes on which the actions are not required in the 
near future, are not excluded from paragraph (f). The commenter also 
states that a simple forecast report with estimated due dates based on 
average airplane utilization cycles can be provided to the Principle 
Maintenance Inspector upon request.
    We partially agree with the commenters, as follows:
    We do not agree to delete paragraph (f) of the final rule. As 
specified in the preamble of the proposed rule, we recognize that doing 
the lap joint modification will require a lengthy maintenance visit, 
within a relatively short compliance time. This makes it necessary for 
operators to do compliance planning to ensure that when the compliance 
deadline is reached all the required actions have been done on all 
affected airplanes. Although plans and schedules can change over time, 
a compliance plan ensures that the operator is aware of the complexity 
of the actions required by this final rule at the start rather than at 
of the end of the compliance period.
    We agree that the requirements specified in paragraph (f) of the 
final rule can be changed to exclude operators that have previously 
done the modification required by either paragraph (g) or (h) of the 
final rule; and by revising the requirement to provide dates and 
maintenance events (e.g., letter checks) to just estimated dates, for 
operators that have not yet done the required actions. Paragraph (f) of 
the final rule has been changed accordingly.

Change Cost Impact Information

    Two commenters ask that the cost impact section of the proposed 
rule be changed.
    One commenter states that the cost impact to the industry is 
underestimated in the proposed rule. The commenter notes that, after 
accomplishing the lap joint modifications on some of its fleet, it 
found that the cost estimates and man hours were 30-40% higher than the 
estimate in the proposed rule. The commenter adds that the amount of 
time required for access and close-up equates to approximately 4 
additional days of downtime in which no revenue can be generated. The 
commenter also states that the estimate of 14 hours to accomplish the 
window corner inspections is on the condition that it is done in 
conjunction with the lap joint modifications, and does not account for 
fastener removal. If the inspection is done separately, the access and 
close-up time would take at least one week.
    Another commenter also asks that the time required for access and 
close-up be added to the proposed rule. The commenter notes that the 
cost impact is particularly useful to operators and the public when a 
proposed compliance period would not allow accomplishment of the 
actions during a scheduled intermediate or heavy maintenance visit. The 
commenter adds that in such cases, access and close-up are direct 
requirements of, and are solely attributable to, the proposed rule, and 
in some cases the out-of-service time and other impacts of unscheduled 
access and close-up may account for nearly all of the actual economic 
impact. The commenter recommends a re-evaluation of the cost impact 
estimated in the proposed rule.
    We do not agree that the cost impact section of the final rule 
should be changed to add in the work hours and cost for access, close-
up, and fastener removal. The cost estimates for the actions required 
by this final rule are estimated over the life of the AD, which is 
approximately 20-25 years. The cost impact section of the final rule 
references paragraph 1.G. of the service bulletin for more detailed 
information, and that section includes, among other things, time 
necessary for access, close-up, and fastener removal. Therefore, 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 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 2,203 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 905 
airplanes of U.S. registry will be affected by this AD.
    Cost estimates for the actions required by this AD for U.S. 
operators over the life of the AD are included in the following table:

----------------------------------------------------------------------------------------------------------------
                                                                                           Cost/
                  Paragraph/AD action                     Number      Work    Parts ($)   Airplane   Total Cost
                                                         affected    hours                  ($)          ($)
----------------------------------------------------------------------------------------------------------------
(a) Lap joint inspection..............................        905        100          0      6,000     5,430,000
----------------------------------------------------------------------------------------------------------------
(f) Compliance planning...............................        905         24          0      1,440     1,303,200
----------------------------------------------------------------------------------------------------------------
(g) Lap joint modification............................        905      4,200     12,000    264,000   238,920,000
----------------------------------------------------------------------------------------------------------------

[[Page 17921]]

 
(h) Lap joint inspection..............................        905        100          0      6,000     5,430,000
----------------------------------------------------------------------------------------------------------------
(i) Post-NACA inspection..............................         25        100          0      6,000       150,000
----------------------------------------------------------------------------------------------------------------
(j) Post-NACA inspection..............................         10        100          0      6,000        60,000
----------------------------------------------------------------------------------------------------------------
(m) Window corner inspection..........................        807         14          0        840       677,880
----------------------------------------------------------------------------------------------------------------

    The cost estimates are based on the following criteria:
     Lap joint inspection cost estimates reflect costs for a 
single inspection cycle, and the work hours vary between groups of 
airplanes. Refer to paragraph 1.G. of Boeing Service Bulletin 737-
53A1177 for more detailed information. An average of 100 work hours was 
used in determining the cost estimates.
     An average of 24 work hours was used in estimating the 
costs for compliance planning.
     Lap joint modification work hours vary between groups of 
airplanes. Refer to paragraph 1.G of Boeing Service Bulletin 737-
53A1177 for more detailed information. An average of 4,200 work hours 
and $12,000 for parts were used in estimating these costs. Modification 
costs are spread over the estimated life of the AD, which is 
approximately 20 to 25 years.
     Window corner inspection work hours vary between groups of 
airplanes. Refer to paragraph 1.G of Boeing Service Bulletin 737-
53A1177 for more detailed information. An average of 14 work hours was 
used in estimating the costs of the inspections only.
    The FAA estimates that during the 10-year period after issuance of 
this AD, worldwide operators will be required to modify 805 Model 737 
series airplanes. The new modification required by this AD will take an 
average of approximately 4,200 work hours to accomplish, at an average 
labor rate of $60 per work hour. The worldwide cost impact of the 
required modification is estimated to be $212,701,000 over 10 years, or 
an average of $21,270,000 per year. The highest impact year is the 
third year after issuance of the AD: an estimated 155 Model 737 series 
airplanes will require modification in that year. Therefore, the 
worldwide cost impact of the modification is estimated to be 
$40,955,000 in that year. The affected Model 737 airplanes operated by 
U.S. operators comprise approximately 41 percent of the total worldwide 
costs. Therefore, the highest cost impact in any given year for the 
modifications is estimated to be $16,791,000 for U.S. operators.
    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. The cost impact figures discussed 
in AD rulemaking actions represent only the time necessary to perform 
the specific actions actually required by the AD. These figures 
typically do not include incidental costs, such as the time required to 
gain access and close up, planning time, or time necessitated by other 
administrative actions.

Regulatory Impact

    The regulations adopted herein will not have a substantial direct 
effect 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, it 
is determined that this final rule does not have federalism 
implications under Executive Order 13132.
    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 removing amendment 39-10179 (62 FR 
55732, October 28, 1997), and by adding a new airworthiness directive 
(AD), amendment 39-12702, to read as follows:

2002-07-08  Boeing: Amendment 39-12702. Docket 98-NM-196-AD. 
Supersedes AD 97-22-07, Amendment 39-10179.

    Applicability: Model 737-200, -200C, -300, -400, and -500 series 
airplanes having line numbers 292 through 2565 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 (o)(1) 
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 find and fix cracking of certain fuselage lap joints, which 
could result in sudden decompression of the airplane, accomplish the 
following:

Repetitive Low Frequency Eddy Current (LFEC) Inspections--Crown Areas

    (a) Do an LFEC inspection to find cracking of the lower skin at 
the lower row of fasteners in the lap joints of the fuselage as 
specified in Part 1.E.1. (``Compliance'') of Boeing Service Bulletin 
737-53A1177, Revision 6, dated May 31, 2001; per PART I 
(``Inspection'') of the Accomplishment Instructions of the service 
bulletin; at the time specified in paragraph (b) or (c) of this AD, 
as applicable.
    (b) For airplanes that have accumulated more than 65,000 total 
flight cycles but not

[[Page 17922]]

more than 70,000 total flight cycles as of the effective date of 
this AD: Do the inspection at the earlier of the times specified in 
paragraphs (b)(1) and (b)(2) of this AD. Repeat the inspection after 
that at intervals not to exceed 1,200 flight cycles until 
accomplishment of the lap joint repair required by paragraph (g) of 
this AD.
    (1) Within 1,200 flight cycles after the effective date of this 
AD.
    (2) Within 1,200 flight cycles after the last inspection, if 
any, accomplished in accordance with AD 97-22-07, amendment 39-
10179.
    (c) For airplanes that have accumulated at least 45,000 total 
flight cycles but not more than 65,000 total flight cycles as of the 
effective date of this AD: Do the inspection at the earlier of the 
times specified in paragraphs (c)(1) and (c)(2) of this AD. Repeat 
the inspection after that at intervals not to exceed 1,200 flight 
cycles until accomplishment of the lap joint repair required by 
paragraph (g) of this AD.
    (1) At the later of the times specified in paragraphs (c)(1)(i) 
and (c)(1)(ii) of this AD.
    (i) Before the accumulation of 50,000 total flight cycles.
    (ii) Within 1,200 flight cycles after the effective date of this 
AD.
    (2) Within 1,200 flight cycles after the last inspection, if 
any, accomplished in accordance with AD 97-22-07, amendment 39-
10179.

Crack Repair

    (d) Except as provided by paragraph (e) of this AD: If any 
cracking is found during any inspection required by this AD, before 
further flight, repair per PART II (``Crack Repair'') of the 
Accomplishment Instructions of Boeing Service Bulletin 737-53A1177, 
Revision 6, dated May 31, 2001.
    (e) If any cracking is found during any inspection required by 
this AD, and Boeing Service Bulletin 737-53A1177, Revision 6, dated 
May 31, 2001, specifies to contact Boeing for repair instructions: 
Repair any cracking, before further flight, per a method approved by 
the Manager, Seattle Aircraft Certification Office (ACO), FAA; or 
per data meeting the type certification basis of the airplane 
approved by a Boeing Company Designated Engineering Representative 
(DER) who has been authorized by the Manager, Seattle ACO, to make 
such findings. For a repair method to be approved by the Manager, 
Seattle ACO, as required by this paragraph, the approval letter must 
specifically reference this AD.

Compliance Plan

    (f) For airplanes on which the applicable lap joint modification 
as required by paragraph (g) or (h) of this AD, as applicable, has 
not been done as of the effective date of this AD: Within 3 months 
after the effective date of this AD, submit a plan to the FAA 
identifying a schedule for compliance with paragraph (g) and (h) of 
this AD, as applicable. This schedule must include, for each of the 
operator's affected airplanes, the estimated dates when the required 
actions will be accomplished. For the purposes of this paragraph, 
``FAA'' means the Principal Maintenance Inspector (PMI) for 
operators that are assigned a PMI, or the cognizant Flight Standards 
District Office for other operators. Information collection 
requirements contained in this regulation have been approved by the 
Office of Management and Budget (OMB) under the provisions of the 
Paperwork Reduction Act of 1980 (44 U.S.C. 3501 et seq.) and have 
been assigned OMB Control Number 2120-0056.

    Note 2: Operators are not required to submit revisions to the 
compliance plan required by paragraph (f) of this AD to the FAA.

Lap Joint Modification (Repair)--Crown Areas

    (g) Except as provided by paragraph (h) of this AD: Install the 
lap joint repair as specified in Part 1.E.1. (``Compliance'') of 
Boeing Service Bulletin 737-53A1177, Revision 4, dated September 2, 
1999; Revision 5, dated February 15, 2001; or Revision 6, dated May 
31, 2001; per PART III or IV (``Lap Joint Repair''), as applicable, 
of the Accomplishment Instructions of the applicable service 
bulletin; at the time specified in paragraph (g)(1), (g)(2), (g)(3), 
(g)(4), or (g)(5) of this AD, as applicable. Accomplishment of this 
repair terminates the repetitive inspections required by paragraphs 
(b), (c), and (j) of this AD.
    (1) For airplanes that have accumulated 70,000 total flight 
cycles or more as of the effective date of this AD: Within 600 
flight cycles after the effective date of this AD, do the lap joint 
repair.
    (2) For airplanes that have accumulated 65,000 total flight 
cycles or more, but less than 70,000 total flight cycles as of the 
effective date of this AD: Do the repair at the later of the times 
specified in paragraphs (g)(2)(i) and (g)(2)(ii) of this AD.
    (i) Before the accumulation of 70,000 total flight cycles.
    (ii) Within 600 flight cycles after the effective date of this 
AD.
    (3) For airplanes that have accumulated 45,000 total flight 
cycles or more, but less than 65,000 total flight cycles as of the 
effective date of this AD: Within 5,000 flight cycles after the 
effective date of this AD.
    (4) For airplanes that have accumulated less than 45,000 total 
flight cycles as of the effective date of this AD: Before the 
accumulation of 50,000 total flight cycles.
    (5) Notwithstanding the times specified in paragraphs (g)(1), 
(g)(2), (g)(3), and (g)(4) of this AD, for airplanes on which the 
``Preventive Change'' (NACA modification) has been accomplished per 
PART III of the Accomplishment Instructions of Boeing Alert Service 
Bulletin 737-53A1177, Revision 1, dated September 19, 1996; Revision 
2, dated July 24, 1997; or Revision 3, dated September 18, 1997: 
Within 18,000 flight cycles after accomplishment of the NACA 
modification.
    (h) For Groups 3 and 5 airplanes as listed in Boeing Service 
Bulletin 737-53A1177, Revision 6, dated May 31, 2001: Install the 
lap joint repair at stringers 4R and 10R, as specified in Part 
1.E.1. (``Compliance'') of Boeing Service Bulletin 737-53A1177, 
Revision 6, dated May 31, 2001; at the time specified in paragraph 
(g)(1), (g)(2), (g)(3), (g)(4), or (g)(5) of this AD, as applicable; 
per a method approved by the Manager, Seattle ACO; or per data 
meeting the type certification basis of the airplane approved by a 
Boeing Company DER who has been authorized by the Manager, Seattle 
ACO, to make such findings. For a repair method to be approved by 
the Manager, Seattle ACO, as required by this paragraph, the 
approval letter must specifically reference this AD.

Repetitive LFEC Inspections--Outside Crown Areas

    (i) Before the accumulation of 70,000 total flight cycles, or 
within 2,500 flight cycles after the effective date of this AD, 
whichever comes later: Do an LFEC inspection to find cracking of the 
lap joints of the fuselage, as specified in Part 1.E.2. 
(``Compliance'') of Boeing Service Bulletin 737-53A1177, Revision 6, 
dated May 31, 2001, and as identified in Figures 2 through 6 of the 
Accomplishment Instructions of the service bulletin. Do the 
inspection per the service bulletin. Repeat the inspection after 
that at intervals not to exceed 5,000 flight cycles.

Post-NACA Modification Inspections--Crown Areas

    (j) For airplanes that have the ``Preventive Change'' (NACA 
modification) of the crown lap joint stringers (``Crown Laps'') done 
per PART III of the Accomplishment Instructions of Boeing Alert 
Service Bulletin 737-53A1177, Revision 1, dated September 19, 1996; 
Revision 2, dated July 24, 1997; or Revision 3, dated September 18, 
1997: Within 12,000 flight cycles after accomplishment of the NACA 
modification, or within 750 flight cycles after the effective date 
of this AD, whichever is later, do either an external (Figure 8) or 
internal (Figure 9) LFEC inspection to find cracking and corrosion 
as specified in Part 1.E.4.a. (``Compliance'') of Boeing Service 
Bulletin 737-53A1177, Revision 6, dated May 31, 2001; per PART I 
(``Inspection'') of the Accomplishment Instructions of Revision 6 of 
the service bulletin.
    (1) If the external inspection is done: Repeat the inspection 
after that at intervals not to exceed 1,500 flight cycles until 
accomplishment of the lap joint repair required by paragraph (g) of 
this AD.
    (2) If the internal inspection is done: Repeat the inspection 
after that at intervals not to exceed 4,500 flight cycles until 
accomplishment of the lap joint repair required by paragraph (g) of 
this AD.

Post-NACA Modification Inspections--Outside Crown Areas

    (k) For airplanes that have the ``Preventive Change'' (NACA 
modification) outside the crown areas done per PART III of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1177, Revision 1, dated September 19, 1996; Revision 2, dated 
July 24, 1997; or Revision 3, dated September 18, 1997: Before the 
accumulation of 20,000 flight cycles after accomplishment of the 
NACA modification or within 750 flight cycles after the effective 
date of this AD, whichever is later, do either an external (Figure 
8) or internal (Figure 9) LFEC inspection to find cracking and 
corrosion as specified in Part 1.E.4.b. (``Compliance'') of Boeing 
Service Bulletin 737-53A1177, Revision 6, dated May 31, 2001, per 
PART I

[[Page 17923]]

(``Inspection'') of the Accomplishment Instructions of Revision 6 of 
the service bulletin.
    (1) If the external inspection is done: Repeat the external 
inspection after that at intervals not to exceed 1,500 flight 
cycles.
    (2) If the internal inspection is done: Repeat the internal 
inspection after that at intervals not to exceed 4,500 flight 
cycles.

Modification of Tear Strap Splice Straps

    (l) For airplanes that have the ``lap joint repair,'' as 
specified in Part IV of the Accomplishment Instructions of Boeing 
Alert Service Bulletin 737-53A1177, Revision 2, dated July 24, 1997, 
or Revision 3, dated September 18, 1997: Within 45,000 flight cycles 
after accomplishment of this lap joint repair, modify the splice 
straps per Figures 10, 11, and 12 of the Accomplishment Instructions 
of Boeing Service Bulletin 737-53A1177, Revision 6, dated May 31, 
2001.

Follow-On LFEC Inspections

    (m) Within 45,000 flight cycles after accomplishment of the lap 
joint repair required by paragraph (g) or (h) of this AD, as 
applicable: Do either an external or internal (Figure 9) LFEC 
inspection as specified in Part 1.E.7. (``Compliance'') of Boeing 
Service Bulletin 737-53A1177, Revision 6, dated May 31, 2001, to 
find cracking of the lap joint repair, per PART I (``Inspection'') 
of the Accomplishment Instructions of the service bulletin. Repeat 
the inspection after that at intervals not to exceed 2,800 flight 
cycles.

Repetitive High Frequency Eddy Current (HFEC) Inspections--Window 
Corners

    (n) For airplanes having line numbers 520 through 2565 
inclusive: Before the accumulation of 50,000 total flight cycles or 
within 2,250 flight cycles after the effective date of this AD, 
whichever comes later, do an HFEC inspection to find cracking as 
specified in Part 1.E.10 (``Compliance'') of Boeing Service Bulletin 
737-53A1177, Revision 6, dated May 31, 2001, per PART V (``Window 
Corner Fastener Hole Cracking, Inspection and Repair'') of the 
Accomplishment Instructions of the service bulletin. Repeat the 
inspection after that at intervals not to exceed 4,500 flight 
cycles. Accomplishment of the modification (which includes removing 
and discarding fasteners, oversizing fastener holes, and installing 
rivets or Hi-Lok fasteners, as applicable), per PART V of the 
Accomplishment Instructions of Boeing Service Bulletin 737-53A1177, 
Revision 5, dated February 15, 2001, or Revision 6, dated May 31, 
2001, constitutes terminating action for the inspections required by 
this paragraph.

Alternative Methods of Compliance

    (o)(1) 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 PMI, who may add comments 
and then send it to the Manager, Seattle ACO.
    (2) Alternative methods of compliance, approved in accordance 
with AD 97-22-07, amendment 39-101-79 are approved as alternative 
methods of compliance with paragraphs (a), (b), (d), (e), (g), and 
(i) of this AD.

    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

    (p) 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.

Incorporation by Reference

    (q) Except as provided by paragraphs (e), (f), and (h) of this 
AD, the actions shall be done in accordance with Boeing Service 
Bulletin 737-53A1177, Revision 4, dated September 2, 1999; Boeing 
Service Bulletin 737-53A1177, Revision 5, dated February 15, 2001; 
or Boeing Service Bulletin 737-53A1177, Revision 6, dated May 31, 
2001, as applicable. This incorporation by reference is 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.

Effective Date

    (r) This amendment becomes effective on May 17, 2002.

    Issued in Renton, Washington, on April 2, 2002.
Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 02-8454 Filed 4-11-02; 8:45 am]
BILLING CODE 4910-13-U