[Federal Register Volume 68, Number 117 (Wednesday, June 18, 2003)]
[Proposed Rules]
[Pages 36515-36518]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-15327]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2001-NM-246-AD]
RIN 2120-AA64


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 737-200, -
200C, -300, -400, and -500 series airplanes. This proposal would 
require repetitive inspections to find fatigue cracking of certain 
upper and lower skin panels of the fuselage, and follow-on and 
corrective actions, if necessary. This proposal also includes 
terminating action for the repetitive inspections of

[[Page 36516]]

certain modified or repaired areas only. This action is necessary to 
find and fix fatigue cracking of the skin panels, which could result in 
sudden fracture and failure of the skin panels of the fuselage, and 
consequent rapid decompression of the airplane. This action is intended 
to address the identified unsafe condition.

DATES: Comments must be received by August 4, 2003.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 2001-NM-246-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. 2001-NM-246-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.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, PO 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: Duong Tran, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 
917-6452; 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:
    [sbull] 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.
    [sbull] For each issue, state what specific change to the proposed 
AD is being requested.
    [sbull] 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 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 2001-NM-246-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. 2001-NM-246-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received reports indicating that cracks were found 
along the edges of the chem-milled pockets in the upper skin at 
stringer S-12, and above the S-4, S-10, and S-14 lap joints, on several 
Boeing Model 737 series airplanes. The cracks were up to 6 inches long 
and multiple adjacent bays were found to be cracked along the same 
stringers on three of the airplanes. The airplanes had accumulated 
between 34,574 and 56,949 total flight cycles. Additionally, skin 
cracks up to 4 inches long located below the S-14 lap joint along the 
bonded skin doublers were reported on 25 other airplanes which had 
accumulated between 22,786 and 80,113 total flight cycles.
    Analysis by the manufacturer revealed that these cracks are caused 
by fatigue due to high bending stresses at the edge of chem-milled 
pockets or bonded skin doublers. Such fatigue cracking could result in 
sudden fracture and failure of the skin panels of the fuselage, and 
consequent rapid decompression of the airplane.

Related Rulemaking

    This proposed AD is related to AD 2002-07-08, amendment 39-12702 
(67 FR 17917, April 12, 2002). That AD references Boeing Service 
Bulletin 737-53A1177, Revision 6, dated May 31, 2001, as the 
appropriate source of service information for accomplishment of the 
specified actions. (The AD also referenced, for accomplishment of 
certain actions, Boeing Alert Service Bulletin 737-53A1177, Revision 1, 
dated September 19, 1996; Revision 2, dated July 24, 1997; Revision 3, 
dated September 18, 1997; Revision 4, dated September 2, 1999; and 
Revision 5, dated February 15, 2001.) That AD is applicable to certain 
Boeing Model 737 series airplanes and 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 AD 
also requires modification of the fuselage lap joints at certain 
locations, which constitutes terminating action for repetitive 
inspections of the modified areas. Additionally, that AD requires 
replacement of a preventive modification with an improved modification.

Explanation of Relevant Service Information

    We have reviewed and approved Boeing Alert Service Bulletin 737-
53A1210, Revision 1, including Appendix A and Evaluation Form, dated 
October 25, 2001. The service bulletin describes procedures for 
repetitive external detailed and eddy current inspections to find 
fatigue cracking of the upper and lower skin panels of the fuselage 
(crown area and lower lobe area) at stringer S-12, and above the S-4, 
S-10, and S-14 lap joints, and repair of any cracking with either a 
permanent or time-limited repair.
    For airplanes on which a time-limited repair is done, Part 4 of the 
service bulletin describes procedures for a subsequent permanent repair 
within 10,000 flight cycles after installation of the time-limited 
repair. Doing a permanent repair eliminates the need for the repetitive 
inspections for the repaired area only.
    For Group 3, 5, 6, and 8 airplanes only, on which no cracking is 
found, Part 5 of the service bulletin provides procedures for a 
preventive modification of the chem-milled pockets in the upper skins 
at stringer S-12, between body station (BS) 500D and BS 520, which 
would end the repetitive inspections for the modified area only.

[[Page 36517]]

    The service bulletin also describes procedures for repetitive 
follow-on visual inspections for cracking of the lower lobe skins from 
S-15L to S-15R between stations 360 and 1016 and in section 41; 
replacement of any loose fasteners with new fasteners; an internal eddy 
current inspection of the skin, tear straps, and lap joint in each 
adjacent bay for cracking; and repair of any cracking found.
    Accomplishment of the actions specified in Service Bulletin 737-
53A1210, Revision 1, is intended to adequately address the identified 
unsafe condition.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require accomplishment of the actions specified in 
the service bulletin described previously, except as discussed below.

Differences Between Proposed AD and Service Bulletin 737-53A1210, 
Revision 1

    The service bulletin specifies that the manufacturer may be 
contacted for disposition of certain repair conditions, but this 
proposed AD would require the repair of those conditions to be done per 
a method approved by the FAA, or per 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.
    The service bulletin recommends that, after installation of a time-
limited repair, an internal eddy current inspection should be done at 
the first ``C-check'' or within 4,000 flight cycles, whichever is last. 
Because ``C-check'' schedules vary among operators, such a nonspecific 
interval would provide no assurance that operators would do the 
inspection within the prescribed schedule. This proposed AD would 
require that the inspection be done within 4,000 flight cycles after 
the repair installation. We find that a 4,000-flight-cycle interval is 
appropriate for affected airplanes to continue to operate without 
compromising safety.
    Although the service bulletin recommends that operators report 
inspection results to the manufacturer, this proposed AD does not 
contain such a reporting requirement.

Interim Action

    This is considered to be interim action for Group 7 airplanes. 
Although the service bulletin described previously does not include the 
inspection of the crown area (upper lobe) for Group 7 airplanes, as 
specified in paragraph (a) of this proposed AD, the manufacturer has 
advised that it currently is developing a new service bulletin to 
address those airplanes. Once the FAA has reviewed and approved the 
service bulletin, we may consider additional rulemaking to mandate 
those inspections.

Cost Impact

    There are approximately 2,200 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 903 airplanes of U.S. 
registry would be affected by this proposed AD.
    It would take approximately 94 work hours per airplane to 
accomplish the proposed inspections of the crown area, at an average 
labor rate of $60 per work hour. Based on these figures, the cost 
impact of these proposed inspections on U.S. operators is estimated to 
be $5,092,920, or $5,640 per airplane, per inspection cycle.
    It would take approximately 96 work hours per airplane to 
accomplish the proposed inspections of the lower lobe area, at an 
average labor rate of $60 per work hour. Based on these figures, the 
cost impact of these proposed inspections on U.S. operators is 
estimated to be $5,201,280, or $5,760 per airplane, per inspection 
cycle.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the proposed requirements 
of this AD action, and that no operator would accomplish those actions 
in the future if this proposed 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.
    Should an operator elect to install the preventive modification, it 
would take approximately 108 work hours to accomplish, at an average 
labor rate of $60 per work hour. Based on these figures, the cost 
impact of the preventive modification is estimated to be $6,480 per 
airplane.

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 2001-NM-246-AD.

    Applicability: Model 737-200, -200C, -300, -400, and -500 series 
airplanes, as listed in Boeing Alert Service Bulletin 737-53A1210, 
Revision 1, dated October 25, 2001; 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 (g) 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.

[[Page 36518]]

    To find and fix fatigue cracking of certain upper and lower skin 
panels of the fuselage, which could result in sudden fracture and 
failure of the skin panels and consequent rapid decompression of the 
airplane, accomplish the following:

External Detailed and Eddy Current Inspections

    (a) For Groups 1 through 6 and Group 8 airplanes: Before the 
accumulation of 35,000 total flight cycles, or within 4,500 flight 
cycles after the effective date of this AD, whichever is later, do 
external detailed and eddy current inspections of the crown area 
skin panels of the fuselage for cracking, per Part 1 and Figure 1 of 
the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, 
Revision 1, including Appendix A and excluding Evaluation Form, 
dated October 25, 2001. Repeat the inspections at least every 4,500 
flight cycles until paragraph (c) or (d)(1)(ii) of this AD has been 
done, as applicable. Although paragraph 1.D. of the service bulletin 
references a reporting requirement, such reporting is not required 
by this AD.

    Note 2: For the purposes of this AD, a detailed inspection is 
defined as: ``An intensive visual examination of a specific 
structural area, system, installation, or assembly to detect damage, 
failure, or irregularity. Available lighting is normally 
supplemented with a direct source of good lighting at intensity 
deemed appropriate by the inspector. Inspection aids such as mirror, 
magnifying lenses, etc., may be used. Surface cleaning and elaborate 
access procedures may be required.''

    (b) For all airplanes: Before the accumulation of 40,000 total 
flight cycles, or within 4,500 flight cycles after the effective 
date of this AD, whichever is later, do an external detailed 
inspection of the lower lobe area and section 41 of the fuselage for 
cracking, per Part 2 and Figure 2 of the Work Instructions of Boeing 
Alert Service Bulletin 737-53A1210, Revision 1, including Appendix A 
and excluding Evaluation Form, dated October 25, 2001. Repeat the 
inspection at least every 9,000 flight cycles until paragraph (d)(2) 
of this AD has been done, as applicable.

Preventive Modification

    (c) For Groups 3, 5, 6, and 8 airplanes: If no cracking is found 
during any inspection required by paragraph (a) of this AD, doing 
the preventive modification of the chem-milled pockets in the upper 
skin as specified in Part 5 of the Work Instructions of Boeing Alert 
Service Bulletin 737-53A1210, Revision 1, including Appendix A and 
excluding Evaluation Form, dated October 25, 2001, ends the 
repetitive inspections for the modified area only.

Corrective Actions

    (d) If any cracking is found during any inspection required by 
paragraph (a) or (b) of this AD, before further flight, do the 
actions specified in paragraphs (d)(1) and (d)(2) of this AD, as 
applicable, per the Work Instructions of Boeing Alert Service 
Bulletin 737-53A1210, Revision 1, including Appendix A and excluding 
Evaluation Form, dated October 25, 2001. Where the service bulletin 
specifies to contact Boeing for repair instructions, before further 
flight, repair 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.
    (1) For cracking of the crown area, do the repair specified in 
either paragraph (d)(1)(i) or (d)(1)(ii) of this AD. Installation of 
the lap joint repair specified in paragraph (g) of AD 2002-07-08, 
amendment 39-12702, is considered acceptable for compliance with the 
corresponding action specified in this paragraph for the lap joint 
areas only.
    (i) Do a time-limited repair per Part 4 of the Work Instructions 
of the service bulletin, then do the actions required by paragraph 
(e) of this AD at the times specified in that paragraph.
    (ii) Do a permanent repair per Part 3 of the Work Instructions 
of the service bulletin. Installation of a permanent repair ends the 
repetitive inspections required by paragraph (a) of this AD for the 
repaired area only.
    (2) For cracking of the lower lobe area and Section 41, repair 
per Part 2 of the Work Instructions of the service bulletin. 
Accomplishment of this repair ends the repetitive inspections 
required by paragraph (b) of this AD for the repaired area only.

Follow-on and Corrective Actions

    (e) If a time-limited repair is done, as specified in paragraph 
(d)(1)(i) of this AD: Do the actions specified in paragraphs (e)(1), 
(e)(2), and (e)(3) of this AD, at the times specified, per the Work 
Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 
1, including Appendix A and excluding Evaluation Form, dated October 
25, 2001.
    (1) Within 3,000 flight cycles after doing the repair: Do a 
general visual inspection of the repaired area for loose fasteners 
per Part 4 of the Work Instructions of the service bulletin. If any 
loose fastener is found, before further flight, replace with a new 
fastener per the service bulletin. Then repeat the inspection at 
least every 3,000 flight cycles until permanent rivets are installed 
in the repaired area, which ends the repetitive inspections for this 
paragraph.
    (2) Within 4,000 flight cycles after doing the repair: Do an 
internal eddy current inspection of the skin, tear straps, and lap 
joint in each adjacent bay of the repaired area for cracking, per 
Part 4 of the Work Instructions of the service bulletin. If any 
cracking is found, before further flight, repair 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 FAA 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.
    (3) Within 10,000 flight cycles after doing the repair: Make the 
repair permanent per Part 4 and Figure 20 of the Work Instructions 
of the service bulletin, which ends the repetitive inspections for 
the repaired area only.

Credit for Actions Done per Previous Service Bulletin

    (f) Inspections, repairs, and preventive modifications done 
before the effective date of this AD per Boeing Alert Service 
Bulletin 737-53A1210, dated December 14, 2000, are acceptable for 
compliance with the corresponding actions required by this AD.

Alternative Methods of Compliance

    (g) 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.

    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 Permit

    (h) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

    Issued in Renton, Washington, on June 11, 2003.
Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 03-15327 Filed 6-17-03; 8:45 am]
BILLING CODE 4910-13-P