[Federal Register Volume 72, Number 101 (Friday, May 25, 2007)]
[Proposed Rules]
[Pages 29280-29282]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E7-10137]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2007-28283; Directorate Identifier 2006-NM-254-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-600, -700, -700C, -800 
and -900 Series Airplanes

AGENCY: Federal Aviation Administration (FAA), Department of 
Transportation (DOT).

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD) 
for certain Boeing Model 737-600, -700, -700C, -800 and -900 series 
airplanes. This proposed AD would require a one-time general visual 
inspection of frames between body station (BS) 360 and BS 907 to 
determine if certain support brackets of the air conditioning (A/C) 
outlet extrusions are installed; medium- and high-frequency eddy 
current inspections for cracking of the frames around the attachment 
holes of the subject brackets; and repair if necessary. This proposed 
AD would also require installing new, improved fittings for all support 
brackets of the A/C outlet extrusions between BS 360 and BS 907. This 
proposed AD results from numerous reports of multiple cracks in the 
frames around the attachment holes of certain support brackets of the 
A/C outlet extrusions. We are proposing this AD to detect and correct 
frame cracking, which, if not corrected, could lead to a severed frame 
that, combined with cracking of the skin lap splice above stringer 10, 
could result in rapid decompression of the airplane.

DATES: We must receive comments on this proposed AD by July 9, 2007.

ADDRESSES: Use one of the following addresses to submit comments on 
this proposed AD.
     DOT Docket Web site: Go to http://dms.dot.gov and follow 
the instructions for sending your comments electronically.
     Government-wide rulemaking Web site: Go to http://www.regulations.gov and follow the instructions for sending your 
comments electronically.
     Mail: Docket Management Facility, U.S. Department of 
Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401, 
Washington, DC 20590.
     Fax: (202) 493-2251.
     Hand Delivery: Room PL-401 on the plaza level of the 
Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    Contact Boeing Commercial Airplanes, P.O. Box 3707, Seattle, 
Washington 98124-2207, for the service information identified in this 
proposed AD.

FOR FURTHER INFORMATION CONTACT: Wayne Lockett, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone (425) 
917-6447; fax (425) 917-6590.

SUPPLEMENTARY INFORMATION:

Comments Invited

    We invite you to submit any relevant written data, views, or 
arguments regarding this proposed AD. Send your comments to an address 
listed in the ADDRESSES section. Include the docket number ``FAA-2007-
28283; Directorate Identifier 2006-NM-254-AD'' at the beginning of your 
comments. We specifically invite comments on the overall regulatory, 
economic, environmental, and energy aspects of the proposed AD. We will 
consider all comments received by the closing date and may amend the 
proposed AD in light of those comments.
    We will post all comments we receive, without change, to http://dms.dot.gov, including any personal information you provide. We will 
also post a report summarizing each substantive verbal contact with FAA 
personnel concerning this proposed AD. Using the search function of 
that Web site, anyone can find and read the comments in any of our 
dockets, including the name of the individual who sent the comment (or 
signed the comment on behalf of an association, business, labor union, 
etc.). You may review DOT's complete Privacy Act Statement in the 
Federal Register published on April 11, 2000 (65 FR 19477-78), or you 
may visit http://dms.dot.gov.

Examining the Docket

    You may examine the AD docket on the Internet at http://dms.dot.gov, or in person at the Docket Management Facility office 
between 9 a.m. and 5 p.m., Monday through Friday, except Federal 
holidays. The Docket Management Facility office (telephone (800) 647-
5227) is located on the plaza level of the Nassif Building at the DOT 
street address stated in the ADDRESSES section. Comments will be 
available in the AD docket shortly after the Docket Management System 
receives them.

Discussion

    We have received numerous reports of multiple cracks in the frame 
around the attachment holes of certain support brackets of the air 
conditioning (A/C) outlet extrusions on Model 737-200, -300, -400, and 
-500 series airplanes. Investigation has revealed that the frame cracks 
occur due to fatigue caused by a combination of forward and aft loads 
from fuselage expansion, and down loads from fuselage deflection on the 
attached structure. The subject frame cracks radiate from one side of 
the attachment hole, nearest the frame flanges; further, frame cracks 
up to 0.6 inch long have also been found on the inboard flange of the 
body station (BS) 907 frame adjacent to the support bracket. With 
continued fatigue cycling, frame cracking, if not corrected, could lead 
to a severed frame that, combined with cracking of the skin lap splice 
above stringer 10, could result in rapid decompression of the airplane.
    The subject area on Model 737-600, -700, -700C, -800 and -900 
series airplanes is almost identical to that on the affected Model 737-
200, -300, -400, and -500 series airplanes. Therefore, certain Model 
737-600, -700, -700C, -800 and -900 series airplanes are subject to the 
unsafe condition revealed on the Model 737-200, -300, -400, and -500 
series airplanes.
    The inspection threshold specified for the Model 737-600, -700, -
700C, -900, and -900 series airplanes is later than the total flight 
cycles accumulated by some Model 737-200, -300, -400, and -500 series 
airplanes with reported cracks. We have determined that this is 
acceptable based on growth rate and cracking pattern of the cracks.

Relevant Service Information

    We have reviewed Boeing Special Attention Service Bulletin 737-25-
1544, dated October 4, 2006. The service bulletin describes procedures 
for doing a general visual inspection (GVI) of the frames between BS 
360 and BS 907 to identify support brackets of the A/C outlet 
extrusions that have a two-rivet attachment fitting. The service 
bulletin also describes procedures for doing medium- and high-frequency 
eddy current (MFEC and HFEC) inspections for cracking of the frames 
around the attachment holes of the identified

[[Page 29281]]

support brackets. The service bulletin also describes frame repair, if 
necessary, which includes installing reinforcing repair angles. The 
service bulletin also describes procedures for installing new, improved 
support fittings for all A/C outlet extrusions between BS 360 and BS 
907. Accomplishing the actions specified in the service information is 
intended to adequately address the unsafe condition.

FAA's Determination and Requirements of the Proposed AD

    We have evaluated all pertinent information and identified an 
unsafe condition that is likely to exist or develop on other airplanes 
of this same type design. For this reason, we are proposing this AD, 
which would require accomplishing the actions specified in the service 
information described previously.

Clarification of Purpose of GVI

    Operators should note that, although the service bulletin indicates 
that the GVI is part of the procedure to detect cracking in the areas 
previously described, the primary intent of the GVI is to determine 
which support brackets between BS 360 and BS 907 are attached to the 
airframe with two rivets. Only those support brackets are subject to 
the inspections for cracking specified by the service bulletin. 
Therefore, this proposed AD would require a GVI to identify those 
support brackets between BS 360 and BS 907 that are attached to the 
airframe with two rivets.

Related Rulemaking

    This unsafe condition may also exist in Boeing Model 737-200, -300, 
-400, and -500 series airplanes. Therefore, we have issued AD 2006-26-
09, Amendment 39-14867 (72 FR 252, January 4, 2007), which has similar 
requirements, to address the unsafe condition in those airplane models. 
That unsafe condition, if uncorrected, could result in a severed frame 
that, combined with existing multi-site damage at the stringer 10 lap 
splice, could result in rapid decompression of the airplane.

Costs of Compliance

    There are about 1,679 airplanes of the affected design in the 
worldwide fleet. This proposed AD would affect about 626 airplanes of 
U.S. registry. The following table provides the estimated costs for 
U.S. operators to comply with this proposed AD, at an average labor 
rate of $80 per work hour. Operators should note that special cold 
working tools and sleeves will be needed if any repair is required, 
which may increase costs.

                                                 Estimated Costs
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             Action                   Work hours             Parts         Cost per airplane      Fleet cost
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General visual inspection.......  1.................  No parts required.  $80...............  $50,080.
MFEC and HFEC inspections.......  Between 170 and     No parts required.  Between $13,600     Up to $10,817,280.
                                   216.                                    and $17,280.
Replace support fittings........  Between 258 and     Between $56,095     Between $76,735     Up to $68,245,894.
                                   346.                and $81,339.        and $109,019.
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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 Findings

    We have determined that this proposed AD would not have federalism 
implications under Executive Order 13132. This proposed AD 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.
    For the reasons discussed above, I certify that the 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. 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.
    We prepared a regulatory evaluation of the estimated costs to 
comply with this proposed AD and placed it in the AD docket. See the 
ADDRESSES section for a location to examine the regulatory evaluation.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the FAA proposes to amend 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. The Federal Aviation Administration (FAA) amends Sec.  39.13 by 
adding the following new airworthiness directive (AD):

Boeing: Docket No. FAA-2007-28283; Directorate Identifier 2006-NM-
254-AD.

Comments Due Date

    (a) The FAA must receive comments on this AD action by July 9, 
2007.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Boeing Model 737-600, -700, -700C, -800 
and -900 series airplanes; certificated in any category; as 
identified in Boeing Special Attention Service Bulletin 737-25-1544, 
dated October 4, 2006.

Unsafe Condition

    (d) This AD results from numerous reports of multiple cracks in 
the frame around the attachment holes of the support bracket of the 
air conditioning (A/C) outlet extrusion. We are issuing this AD to 
detect and correct

[[Page 29282]]

frame cracking, which, if not corrected, could lead to a severed 
frame that, combined with cracking of the skin lap splice above 
stringer 10, could result in rapid decompression of the airplane.

Compliance

    (e) You are responsible for having the actions required by this 
AD performed within the compliance times specified, unless the 
actions have already been done.

Service Bulletin Reference

    (f) The term ``service bulletin,'' as used in this AD, means 
Boeing Special Attention Service Bulletin 737-25-1544, dated October 
4, 2006.

Inspections

    (g) Before the accumulation of 36,000 total flight cycles, or 
within 72 months after the effective date of this AD, whichever 
occurs later: Do a general visual inspection to determine if the 
support bracket of any A/C outlet extrusion between body station 
(BS) 360 and BS 907 has a two-rivet attachment fitting, then do the 
actions described by paragraph (g)(1) and (g)(2) of this AD; in 
accordance with part 2 of the accomplishment instructions of the 
service bulletin.
    (1) For any subject support bracket not attached with a two-
rivet attachment fitting, no further action is required by paragraph 
(g) of this AD.
    (2) For any subject support bracket having a two-rivet 
attachment fitting, do medium- and high-frequency eddy current 
inspections for cracking of the frame around the attachment holes of 
the support bracket. If any cracking is discovered, before further 
flight, repair the cracking in accordance with part 3 of the 
accomplishment instructions of the service bulletin.

Modification

    (h) Before the accumulation of 36,000 total flight cycles, or 
within 72 months after the effective date of this AD, whichever 
occurs later, replace the support fittings of all A/C outlet 
extrusions between BS 360 and BS 907 with new, improved support 
fittings, in accordance with part 4 of the accomplishment 
instructions of the service bulletin.

Alternative Methods of Compliance (AMOCs)

    (i)(1) The Manager, Seattle Aircraft Certification Office (ACO), 
FAA, has the authority to approve AMOCs for this AD, if requested in 
accordance with the procedures found in 14 CFR 39.19.
    (2) To request a different method of compliance or a different 
compliance time for this AD, follow the procedures in 14 CFR 39.19. 
Before using any approved AMOC on any airplane to which the AMOC 
applies, notify your appropriate principal inspector (PI) in the FAA 
Flight Standards District Office (FSDO), or lacking a PI, your local 
FSDO.
    (3) 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 Commercial Airplanes 
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 repair must meet the certification basis 
of the airplane, and the approval must specifically refer to this 
AD.

    Issued in Renton, Washington, on May 15, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
 [FR Doc. E7-10137 Filed 5-24-07; 8:45 am]
BILLING CODE 4910-13-P