Document ID: FAA-2007-0004-0047
Agency: faa
Document Type: Notice
Title: Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes
Posted Date: 2007-08-24T04:00Z

[Federal Register: August 24, 2007 (Volume 72, Number 164)]
[Proposed Rules]               
[Page 48597-48600]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr24au07-17]                         

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2007-29043; Directorate Identifier 2007-NM-177-AD]
RIN 2120-AA64

 
Airworthiness Directives; Boeing Model 737-300, -400, and -500 
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 all Boeing Model 737-300, -400, and -500 series airplanes. This 
proposed AD would require revising the FAA-approved maintenance 
inspection program to include inspections that will give no less than 
the required damage tolerance rating for each structural significant 
item (SSI), doing repetitive inspections to detect cracks of all SSIs, 
and repairing cracked structure. This proposed AD results from a report 
of incidents involving fatigue cracking and corrosion in transport 
category airplanes that are approaching or have exceeded their design 
service objective. We are proposing this AD to maintain the continued 
structural integrity of the entire fleet of Model 737-300, -400, and -
500 series airplanes.

DATES: We must receive comments on this proposed AD by October 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: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue, SE., Washington, DC 20590.
     Fax: (202) 493-2251.
     Hand Delivery: Room W12-140 on the ground floor of the 
West Building, 1200 New Jersey Avenue, SE., 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: Nancy Marsh, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone (425) 
917-6440; 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-
29043; Directorate Identifier 2007-NM-177-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 Operations office between 9 

a.m. and 5 p.m., Monday through Friday, except Federal holidays. The 
Docket Operations office (telephone (800) 647-5527) is located on the 
ground level of the West 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

    In the early 1980's, as part of its continuing work to maintain the 
structural integrity of older transport category airplanes, we 
concluded that the incidence of fatigue cracking may increase as these 
airplanes reach or exceed their design service objective (DSO). In 
light of this, and as a result of increased utilization, and longer 
operational lives, we determined that a supplemental structural 
inspection program (SSIP) was necessary to maintain the continued 
structural integrity for all airplanes in the transport fleet.

Issuance of Advisory Circular (AC)

    As a follow-on from that determination, we issued AC No. 91-56, 
``Supplemental Structural Inspection Program for Large Transport 
Category Airplanes,'' dated May 6, 1981. That AC provides guidance 
material to manufacturers and operators for use in developing a 
continuing structural integrity program to ensure safe operation of 
older airplanes throughout their operational lives. This guidance 
material applies to transport airplanes that were certified under the 
fail-safe requirements of part 4b (``Airplane Airworthiness, Transport 
Categories'') of the Civil Air Regulations or damage tolerance 
structural requirements of part 25 (``Airworthiness Standards: 
Transport Category Airplanes'') of the Federal Aviation Regulations 
(FAR) (14 CFR part 25), and that have a maximum gross weight greater 
than 75,000 pounds. The procedures set forth in that AC are applicable 
to transport category

[[Page 48598]]

airplanes operated under subpart D (``Special Flight Operations'') of 
part 91 of the FAR (14 CFR part 91); part 121 (``Operating 
Requirements: Domestic, Flag, and Supplemental Operations''); part 125 
(``Certification and Operations: Airplanes having a Seating Capacity of 
20 or More Passengers or a Maximum Payload of 6,000 Pounds or More''); 
and part 135 (``Operating Requirements: Commuter and On-Demand 
Operations'') of the FAR (14 CFR parts 121, 125, and 135). The 
objective of the SSIP was to establish inspection programs to ensure 
timely detection of fatigue cracking.

Development of the SSIP

    In order to evaluate the effect of increased fatigue cracking with 
respect to maintaining fail-safe design and damage tolerance of the 
structure of Boeing Model 737-300, -400, and -500 series airplanes, 
Boeing conducted a structural reassessment of those airplanes, using 
damage tolerance evaluation techniques. Boeing accomplished this 
reassessment using the criteria contained in AC No. 91-56, as well as 
Amendment 25-45 of section 25.571 (``Damage-tolerance and fatigue 
evaluation of structure'') of the FAR (14 CFR 25.571). During the 
reassessment, members of the airline industry participated with Boeing 
in working group sessions and developed the SSIP for Model 737-300, -
400, and -500 series airplanes. Engineers and maintenance specialists 
from the FAA also supported these sessions. Subsequently, based on the 
working group's recommendations, Boeing developed the Supplemental 
Structural Inspection Document (SSID).

Relevant Service Information

    We have reviewed Boeing Models 737-300/400/500 Airplanes Document 
No. D6-82669, ``Supplemental Structural Inspection Document,'' Original 
Release, dated May 2007 (hereafter ``the SSID''). The SSID describes 
procedures for revising the FAA-approved maintenance inspection program 
to include inspections that will give no less than the required damage 
tolerance rating (DTR) for each supplemental significant item (SSI), 
doing repetitive inspections to detect cracks of all SSIs, and 
repairing cracked structure. Accomplishing the actions specified in the 
SSID 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 the following actions:
    Paragraph (g) of the proposed AD would require incorporation of a 
revision into the FAA-approved maintenance inspection program that 
provides no less than the required DTR for each SSI listed in the SSID.
    Paragraph (h) of the proposed AD would require repetitive 
inspections to detect cracks of all SSIs.
    Paragraph (i) of the proposed AD would require repairing any 
cracked structure in accordance with a method approved by the FAA or an 
Authorized Representative (AR) for the Boeing Commercial Airplanes 
Delegation Option Authorization Organization who has been authorized by 
the FAA to make those findings.
    Paragraph (j) of the proposed AD specifies the requirements of the 
inspection program for transferred airplanes. Before any airplane that 
is subject to this proposed AD can be added to an air carrier's 
operations specifications, a program for doing the inspections required 
by this proposed AD must be established.

Differences Between the Proposed AD and Service Information

    Section 3.0, ``Structural Significant Items (SSIs)'' of the SSID 
specifies a threshold of 66,000 flight cycles for accomplishing the 
initial inspections; however, it does not specify a grace period for 
airplanes that are near or have passed that threshold. This proposed AD 
would allow a grace period of 12 months after the effective date of the 
AD to incorporate the SSID into the FAA-approved maintenance inspection 
program. This proposed AD also would allow a grace period of 4,000 
flight cycles measured from 12 months after the effective date of the 
AD to initiate the applicable inspections to detect cracks of all SSIs.
    The SSID does not specify instructions on how to repair certain 
conditions. This proposed AD would require repairing those conditions 
in one of the following ways:
     Using a method that we approve; or
     Using data that have been approved by an AR for the Boeing 
Commercial Airplanes Delegation Option Authorization Organization whom 
we have authorized to make those findings.

Costs of Compliance

    There are about 1,961 airplanes of the affected design in the 
worldwide fleet. The following table provides the estimated costs for 
U.S. operators to comply with this proposed AD.

                                                                     Estimated Costs
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                        Number of U.S.-
             Action                  Work hours       Average labor                 Cost                  registered               Fleet cost
                                                      rate per hour                                        airplanes
--------------------------------------------------------------------------------------------------------------------------------------------------------
Revision of maintenance          1,200 per operator             $80  $96,000 per operator.............             599  $2,496,000.
 inspection program.              (26 U.S.
                                  operators).
Inspections....................  600 per airplane..              80  $48,000, per airplane, per                    599  $28,752,000 per inspection
                                                                      inspection cycle.                                  cycle.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    The number of inspection work hours, as indicated above, is 
presented as if the accomplishment of the actions in this proposed AD 
are to be conducted as ``stand alone'' actions. However, in actual 
practice, these actions for the most part will be done coincidentally 
or in combination with normally scheduled airplane inspections and 
other maintenance program tasks. Therefore, the actual number of 
necessary additional inspection work hours will be minimal in many 
instances. Additionally, any costs associated with special airplane 
scheduling will be minimal.
    Further, compliance with this proposed AD would be a means of 
compliance with the aging airplane safety final rule (AASFR) for the 
baseline structure of Model 737-300, -400, and -500 series airplanes. 
The AASFR final rule requires certain operators to incorporate damage 
tolerance inspections into their maintenance inspection programs. These 
requirements are described in 14

[[Page 48599]]

CFR 121.370(a) and 129.16. Accomplishment of the actions required by 
this proposed AD will meet the requirements of these CFR sections for 
the baseline structure. The costs for accomplishing the inspection 
portion of this proposed AD were accounted for in the regulatory 
evaluation of the AASFR final rule.

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-2007-29043; Directorate Identifier 2007-NM-
177-AD.

Comments Due Date

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

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to all Boeing Model 737-300, -400, and -500 
series airplanes, certificated in any category.

Unsafe Condition

    (d) This AD results from a report of incidents involving fatigue 
cracking and corrosion in transport category airplanes that are 
approaching or have exceeded their design service objective. We are 
issuing this AD to maintain the continued structural integrity of 
the entire fleet of Model 737-300, -400, and -500 series airplanes.

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 Information

    (f) The term ``the SSID,'' as used in this AD, means Boeing 
Models 737-300/400/500 Airplanes Document No. D6-82669, 
``Supplemental Structural Inspection Document,'' Original Release, 
dated May 2007.

Revision of the FAA-Approved Maintenance Inspection Program

    (g) Before the accumulation of 66,000 total flight cycles, or 
within 12 months after the effective date of this AD, whichever 
occurs later, incorporate a revision into the FAA-approved 
maintenance inspection program that provides no less than the 
required damage tolerance rating (DTR) for each structural 
significant item (SSI) listed in the SSID. (The required DTR value 
for each SSI is listed in the SSID.) The revision to the maintenance 
inspection program must include and must be implemented in 
accordance with the procedures in Section 5.0, ``Damage Tolerance 
Rating (DTR) System Application,'' and Section 6.0, ``SSI 
Discrepancy Reporting'' of the SSID. Under the provisions of the 
Paperwork Reduction Act of 1980 (44 U.S.C. 3501 et seq.), the Office 
of Management and Budget (OMB) has approved the information 
collection requirements contained in this AD and has assigned OMB 
Control Number 2120-0056.

Initial and Repetitive Inspections

    (h) Before the accumulation of 66,000 total flight cycles, or 
within 4,000 flight cycles measured from 12 months after the 
effective date of this AD, whichever occurs later, do the applicable 
initial inspections to detect cracks of all SSIs, in accordance with 
the SSID. Repeat the applicable inspections thereafter at the 
intervals specified in Section 3.0, ``Implementation'' of the SSID.

Repair

    (i) If any cracked structure is found during any inspection 
required by paragraph (h) of this AD, before further flight, repair 
the cracked structure using a method approved in accordance with the 
procedures specified in paragraph (k) of this AD.

Inspection Program for Transferred Airplanes

    (j) Before any airplane that is subject to this AD and that has 
exceeded the applicable compliance times specified in paragraph (h) 
of this AD can be added to an air carrier's operations 
specifications, a program for the accomplishment of the inspections 
required by this AD must be established in accordance with paragraph 
(j)(1) or (j)(2) of this AD, as applicable.
    (1) For airplanes that have been inspected in accordance with 
this AD: The inspection of each SSI must be done by the new operator 
in accordance with the previous operator's schedule and inspection 
method, or the new operator's schedule and inspection method, at 
whichever time would result in the earlier accomplishment for that 
SSI inspection. The compliance time for accomplishment of this 
inspection must be measured from the last inspection accomplished by 
the previous operator. After each inspection has been done once, 
each subsequent inspection must be performed in accordance with the 
new operator's schedule and inspection method.
    (2) For airplanes that have not been inspected in accordance 
with this AD: The inspection of each SSI required by this AD must be 
done either before adding the airplane to the air carrier's 
operations specification, or in accordance with a schedule and an 
inspection method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA. After each inspection has been done 
once, each subsequent inspection must be done in accordance with the 
new operator's schedule.

Alternative Methods of Compliance (AMOCs)

    (k)(1) The Manager, Seattle ACO, 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

[[Page 48600]]

(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 approval must specifically refer 
to this AD.

    Issued in Renton, Washington, on August 12, 2007.
Stephen P. Boyd,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. E7-16668 Filed 8-23-07; 8:45 am]

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