[Federal Register Volume 70, Number 62 (Friday, April 1, 2005)]
[Proposed Rules]
[Pages 16761-16764]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-6451]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2002-NM-289-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, and -200C 
Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Supplemental notice of proposed rulemaking (NPRM); reopening of 
comment period.

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SUMMARY: This document revises an earlier NPRM, applicable to all 
Boeing Model 737-100, -200, and -200C series airplanes. The original 
NPRM would have required repetitive inspections to detect discrepancies 
of certain fuselage skin panels located just aft of the wheel well, and 
repair if necessary. The original NPRM was prompted by reports of 
fatigue cracking of the skins and doublers located aft of the wing, 
between body station (BS) 727 and BS 1016, and between body stringers 
14 and 25. This supplemental NPRM revises the original NPRM by adding 
requirements for certain airplanes, revising the compliance time for 
inspection of modified skin areas, and allowing alternative service 
information for certain actions. The actions specified by this new 
supplemental NPRM are intended to detect and correct fatigue cracking 
of the skin panels, which could cause rapid decompression of the 
airplane. This action is intended to address the identified unsafe 
condition.

DATES: Comments must be received by April 26, 2005.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 2002-NM-289-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9 a.m. and 3 p.m., Monday through Friday, except 
Federal holidays. Comments may be submitted via fax to (425) 227-1232. 
Comments may also be sent via the Internet using the following address: 
[email protected]. Comments sent via fax or the Internet must 
contain ``Docket No. 2002-NM-289-AD'' in the subject line and need not 
be submitted in triplicate. Comments sent via the Internet as attached 
electronic files must be formatted in Microsoft Word 97 for Windows or 
ASCII text.
    For the service information referenced in the proposed rule, 
contact Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Suzanne Lucier, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 
917-6438; fax (425) 917-6590.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this action may be changed in 
light of the comments received.
    Submit comments using the following format:
     Organize comments issue-by-issue. For example, discuss a 
request to change the compliance time and a request to change the 
service bulletin reference as two separate issues.
     For each issue, state what specific change to the proposed 
AD is being requested.
     Include justification (e.g., reasons or data) for each 
request.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this

[[Page 16762]]

proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this action must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 2002-NM-289-AD.'' The postcard will be date stamped 
and returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 2002-NM-289-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    A proposal to amend part 39 of the Federal Aviation Regulations (14 
CFR part 39) to add an airworthiness directive (AD), applicable to all 
Boeing Model 737-100, -200, and -200C series airplanes, was published 
as a notice of proposed rulemaking (NPRM) in the Federal Register on 
January 7, 2004 (69 FR 897). That NPRM would have required repetitive 
inspections to detect discrepancies of certain fuselage skin panels 
located just aft of the wheel well, and repair if necessary. That NPRM 
was prompted by reports of fatigue cracking of the skins and doublers 
located aft of the wing, between body station (BS) 727 and BS 1016, and 
between body stringers 14 and 25, on numerous Boeing Model 737-100, -
200, and -200C series airplanes. The cracking has been attributed to 
fatigue from a combination of shear stresses due to repeated wrinkling 
of the skin, and the skin chem-milled pockets configuration. Such 
fatigue cracking, if not corrected, could cause rapid decompression of 
the airplane.

Actions Since Original NPRM Was Issued

    Due consideration has been given to the comments received in 
response to the original NPRM.

Request To Revise Inspection References

    Paragraph (b) of the original NPRM refers to Boeing Service 
Bulletin 737-53-1065, Revision 2, dated April 19, 2001, for conditions 
associated with the inspection requirements. One commenter (the 
manufacturer) requests that we revise that service bulletin reference 
to include earlier revision levels. The manufacturer recommends that we 
require inspections of all previously modified airplanes having 
stiffening angles--regardless of the service bulletin revision used.
    We agree that (stiffener) modifications for airplanes modified in 
accordance with the original issue and Revision 1 of the service 
bulletin should also be inspected. Excluding these earlier service 
bulletin versions was an oversight in the development of the original 
NPRM. We have revised paragraphs (b) and (c) of this supplemental NPRM 
accordingly.

Request To Revise Compliance Time

    The manufacturer requests that we revise paragraph (b) of the 
original NPRM (inspection of modified skin areas) to also change the 
compliance time: from 16,000 flight cycles after the modification to 
16,000 total accumulated flight cycles. Post-modification cracks have 
been found in service, which the manufacturer believes existed when the 
modification was installed but were visually undetectable at the time. 
The modification with the stiffening angles is designed to prevent 
shear wrinkling by breaking up the bay into smaller dimensions. These 
angles do not reduce the hoop stress in the areas where the cracks 
typically exist. As a result, cracks that exist when the modification 
is installed will continue to propagate under hoop loading and may grow 
to a significant length before the airplane accumulates an additional 
16,000 flight cycles after the modification. The manufacturer concludes 
that the compliance time for the initial inspection of modified areas 
should be based on the total accumulated flight cycles, and not the 
flight cycles accumulated since the modification.
    We agree. We have revised the compliance time in paragraph (b) of 
this supplemental NPRM accordingly.

Conclusion

    Since these changes expand the scope of the original NPRM, we have 
determined that it is necessary to reopen the comment period to provide 
additional opportunity for public comment. Additional comments on the 
original NPRM are addressed below.

Request To Allow Additional Repair Information

    Two commenters request that we revise the original NPRM to include 
the Boeing 737 Structural Repair Manual (SRM) as an acceptable source 
of service information for compliance with the repair requirements 
specified in paragraphs (d)(1)(iii) and (d)(2). The commenters state 
that, since Boeing issued Service Bulletin 737-53-1065, Revision 2, 
dated April 19, 2001 (cited in the original NPRM), the SRM has been 
revised to include repair procedures for skin cracks. The repairs in 
Section 53-30-3, Figure 48, of the SRM apply to most of the areas 
covered by the original NPRM. The commenters note that Figure 48 of the 
SRM is an FAA-approved repair for this type of damage; allowing this 
optional repair in the original NPRM will reduce the number of repair 
inquiries from operators. Therefore, the commenters request that crack 
repairs in accordance with the SRM also be allowed in paragraphs 
(d)(1)(iii) and (d)(2) of the original NPRM.
    We agree with the commenters' request and have changed paragraphs 
(d)(1)(iii) and (d)(2) accordingly in this supplemental NPRM.

Request To Clarify Requirement

    One commenter, the manufacturer, states that cracks underneath 
external repair doublers (installed for repairs unrelated to the 
requirements specified in this proposed AD) have been found in service. 
The commenter requests that we revise paragraphs (a) and (c) of the 
original NPRM to also address inspections of chemical-milled steps 
underneath external repair doublers. Undetected cracks that are not 
sufficiently spanned by a repair doubler could propagate undetected. 
The commenter suggests that an FAA-approved repair with three rows of 
fasteners on each side of the chemical-milled step would be adequate to 
maintain ultimate load capability even if undetected cracks develop 
underneath the repair.
    We agree with the request. External repair doublers impede the 
ability to inspect the exterior of fuselage side skins. The commenter's 
suggested change would provide adequate inspection procedures for the 
skin under the repair doublers. We find the commenter's suggestion 
satisfactory and have included new paragraph (g) of this supplemental 
NPRM to provide inspection procedures for those airplanes as one method 
of compliance with the requirements of paragraphs (a) and (c) of this 
supplemental NPRM.

Request To Limit Repetitive Inspections

    This same commenter requests that we revise the repetitive 
inspection requirement specified in paragraph (d)(1)(ii) of the 
original NPRM to a one-time-only inspection after the time-limited 
repair has been done, as specified in the service bulletin.
    We agree with the request. Eliminating the repetitive inspections 
will not compromise safety. We have changed paragraph (d)(1)(ii) in 
this

[[Page 16763]]

supplemental NPRM to correspond to the compliance times of Service 
Bulletin 737-53-1065.

Changes to 14 CFR Part 39/Effect on Supplemental NPRM

    On July 10, 2002, the FAA issued a new version of 14 CFR part 39 
(67 FR 47997, July 22, 2002), which governs the FAA's airworthiness 
directives system. The regulation now includes material that relates to 
altered products, special flight permits, and alternative methods of 
compliance (AMOCs). These changes are reflected in this supplemental 
NPRM.

Explanation of Additional Changes to Supplemental NPRM

    Boeing has received a Delegation Option Authorization (DOA). We 
have revised paragraph (e) of this supplemental NPRM to allow any 
discrepancy, including cracking, to be repaired according to data that 
conform to the airplane's type certificate and that are approved by an 
Authorized Representative for the Boeing DOA Organization (rather than 
the Designated Engineering Representative (DER)) whom we have 
authorized to make such findings.
    We have also revised paragraph (h)(2) of this supplemental NPRM to 
delegate the authority to approve an alternative method of compliance 
for any repair required by the AD to the Authorized Representative for 
the Boeing DOA Organization rather than the DER.

Interim Action

    This is considered to be interim action. The manufacturer has 
advised that it is developing an improved preventive modification 
intended to address the identified unsafe condition for unmodified skin 
areas. After this modification is developed, approved, and available, 
we may consider additional rulemaking.

Cost Impact

    There are about 1,000 airplanes of the affected design in the 
worldwide fleet. The FAA estimates that 390 airplanes of U.S. registry 
would be affected by this supplemental NPRM.
    The inspection would take about 47 to 88 work hours per airplane 
(depending on configuration), at an average labor rate of $65 per work 
hour. Based on these figures, we estimate the cost of the inspection to 
be $3,055 to $5,720 per airplane, per inspection cycle.
    The cost impact figure discussed above is based on assumptions that 
no operator has yet accomplished any of the proposed requirements of 
this AD action, and that no operator would accomplish those actions in 
the future if this AD were not adopted. 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.

Authority for This Rulemaking

    Title 49 of the United States Code specifies the FAA's authority to 
issue rules on aviation safety. Subtitle I, section 106, describes the 
authority of the FAA Administrator. Subtitle VII, Aviation Programs, 
describes in more detail the scope of the Agency's authority.
    We are issuing this rulemaking under the authority described in 
subtitle VII, part A, subpart III, section 44701, ``General 
requirements.'' Under that section, Congress charges the FAA with 
promoting safe flight of civil aircraft in air commerce by prescribing 
regulations for practices, methods, and procedures the Administrator 
finds necessary for safety in air commerce. This regulation is within 
the scope of that authority because it addresses an unsafe condition 
that is likely to exist or develop on products identified in this 
rulemaking action.

Regulatory Impact

    The regulations proposed herein would 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 proposal would not have federalism implications 
under Executive Order 13132.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act. A copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec.  39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

Boeing: Docket 2002-NM-289-AD.

    Applicability: All Model 737-100, -200, and -200C series 
airplanes; certificated in any category.
    Compliance: Required as indicated, unless accomplished 
previously.
    To detect and correct fatigue cracking of the skin panels, which 
could cause rapid decompression of the airplane, accomplish the 
following:

Repetitive Inspections: Unmodified Skin Areas

    (a) For fuselage skin panel areas that have not been modified 
with stiffening angles: Before the airplane accumulates 16,000 total 
flight cycles, or within 4,500 flight cycles after the effective 
date of this AD, whichever occurs later, inspect the unmodified 
fuselage side skins just aft of the main wheelwell, and perform all 
follow-on actions, in accordance with Part I of the Accomplishment 
Instructions of Boeing Service Bulletin 737-53-1065, Revision 2, 
dated April 19, 2001; except as provided by paragraph (g) of this 
AD. If no cracking, loose fasteners, disbonding, or damage is found: 
Repeat the inspection at the time specified in paragraph 1.E., 
Compliance, of the service bulletin, as applicable, except as 
provided by paragraph (d) of this AD.

Repetitive Inspections: Modified Skin Areas

    (b) For fuselage skin panel areas that have been modified with 
stiffening angles in accordance with Boeing Service Bulletin 737-53-
1065, dated January 4, 1985; Revision 1, dated October 12, 1989; or 
Revision 2, dated April 19, 2001: Before the airplane accumulates 
16,000 total flight cycles, or within 4,500 flight cycles after the 
effective date of this AD, whichever occurs later, inspect the 
modified areas as specified in accordance with Part I of Boeing 
Service Bulletin 737-53-1065, Revision 2, dated April 19, 2001. 
Repeat the inspection at the time specified in paragraph 1.E., of 
the service bulletin, as applicable, except as provided by paragraph 
(d) of this AD. If any cracks, loose fasteners, disbonding, or

[[Page 16764]]

damage is found: Repair before further flight in accordance with the 
requirements of paragraph (d) of this AD.

Terminating Action for Inspections of Modified Skin Areas

    (c) For fuselage skin panel areas that have been modified with 
stiffening angles in accordance with Boeing Service Bulletin 737-53-
1065, dated January 4, 1985; Revision 1, dated October 12, 1989; or 
Revision 2, dated April 19, 2001: At the later of the times 
specified by paragraphs (c)(1) and (c)(2) of this AD, perform a 
subsurface eddy current or magneto optical imaging inspection to 
detect subsurface skin cracks along the edge of the bonded doubler, 
in accordance with Figure 10 of Boeing Service Bulletin 737-53-1065, 
Revision 2, dated April 19, 2001; except as provided by paragraph 
(g) of this AD. If any cracks are found, repair before further 
flight in accordance with paragraph (d) of this AD. Accomplishment 
of this inspection and all applicable corrective actions terminates 
the repetitive inspections required by paragraph (b) of this AD for 
the modified areas.
    (1) Inspect within 24,500, but not fewer than 20,000, flight 
cycles after the modification of the skin.
    (2) Inspect within 4,500 flight cycles after the effective date 
of this AD.

Repair: Modified and Unmodified Skin Areas

    (d) If any cracking is detected during any inspection required 
by this AD: Do the actions specified by paragraph (d)(1) or (d)(2) 
of this AD before further flight. Do the actions in accordance with 
Boeing Service Bulletin 737-53-1065, Revision 2, dated April 19, 
2001, except as required by paragraph (e) of this AD.
    (1) Do a time-limited repair (including a detailed inspection of 
the skin in the area of the repair to detect corrosion and doubler 
disbonding) in accordance with Part III of the Accomplishment 
Instructions of the service bulletin.
    (i) After the time-limited repair has been accomplished: At 
intervals not to exceed 3,000 flight cycles, perform an external 
general visual inspection of the repair to detect loose or missing 
fasteners, in accordance with Part III of the Accomplishment 
Instructions of the service bulletin, until the actions specified in 
paragraph (d)(1)(v) of this AD have been accomplished.
    (ii) Within 4,500 flight cycles after the time-limited repair 
has been accomplished: Perform an internal inspection of the repair 
to detect cracking or doubler disbonding using general visual and 
high-frequency eddy current methods, in accordance with Figure 11 of 
the service bulletin, unless the actions specified in paragraph 
(d)(1)(v) of this AD have been accomplished.
    (iii) If any cracking is found during any inspection required by 
paragraph (d)(1) of this AD: Repair before further flight in 
accordance with paragraph (e) of this AD. Another approved repair 
method is in Section 53-30-3, Figure 48, of the Boeing 737 
Structural Repair Manual (SRM).
    (iv) If any disbonding is found during any inspection required 
by paragraph (d)(1) of this AD: Repair before further flight in 
accordance with Part II of the service bulletin.
    (v) Within 10,000 flight cycles after accomplishment of the 
time-limited repair: Make the repair permanent in accordance with 
Part III of the Accomplishment Instructions of the service bulletin. 
Permanent repair of an area terminates the repetitive inspections 
specified in this AD for that repaired area only.
    (2) Do a permanent repair (including an inspection using 
external subsurface eddy current or magneto optical imaging methods 
to detect cracks at the chem-milled step in each adjacent bay of the 
fuselage skin, a detailed inspection of the skin in the area of the 
repair for corrosion and doubler disbonding, and applicable 
corrective action) of the cracked area, in accordance with Part II 
of the Accomplishment Instructions of the service bulletin. Another 
approved repair method is in Section 53-30-3, Figure 48, of the 
Boeing 737 Structural Repair Manual (SRM). Permanent repair of an 
area terminates the repetitive inspections specified in this AD for 
that repaired area only.

Exceptions to Service Bulletin Procedures

    (e) During any inspection required by this AD, if any 
discrepancy (including cracking) is detected for which the service 
bulletin specifies to contact Boeing for appropriation action: 
Before further flight, repair according to a method approved by the 
Manager, Seattle Aircraft Certification Office (ACO); or according 
to data meeting the certification basis of the airplane approved by 
an Authorized Representative for the Boeing Delegation Option 
Authorization Organization who has been authorized by the Manager, 
Seattle ACO, to make those findings. For a repair method to be 
approved, the approval must specifically refer to this AD.
    (f) Although Boeing Service Bulletin 737-53-1065, Revision 2, 
dated April 19, 2001, recommends that cracks found in Zone 2 be 
reported to Boeing, this AD does not require such a report.
    (g) For airplanes subject to the requirements of paragraphs (a) 
and (c) of this AD: Inspections are not required in areas that are 
spanned by an FAA-approved repair that has a minimum of 3 rows of 
fasteners above and below the chemical-milled step. If an external 
doubler covers the chemical-milled step, but does not span it by a 
minimum of 3 rows of fasteners above and below, one method of 
compliance with the inspection requirement of paragraphs (a) and (c) 
of this AD is to inspect all chemical-milled steps covered by the 
repair using internal nondestructive test (NDT) methods in 
accordance with Part 6, Subject 53-30-20, of the Boeing 737 NDT 
Manual. Follow-on and corrective actions must be done as specified 
in this AD.

Alternative Methods of Compliance (AMOCs)

    (h)(1) In accordance with 14 CFR 39.19, the Manager, Seattle 
ACO, FAA, is authorized to approve AMOCs for this AD.
    (2) An AMOC that provides an acceptable level of safety may be 
used for any repair required by this AD, if it is approved by an 
Authorized Representative for the Boeing Delegation Option 
Authorization Organization who has been authorized by the Manager, 
Seattle ACO, to make those findings. For a repair method to be 
approved, the approval must specifically refer to this AD.

    Issued in Renton, Washington, on March 22, 2005.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 05-6451 Filed 3-31-05; 8:45 am]
BILLING CODE 4910-13-P