737- skin crack inspections

[Federal Register: September 20, 2007 (Volume 72, Number 182)]
[Proposed Rules]
[Page 53706-53709]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr20se07-18]

-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2007-29255; Directorate Identifier 2007-NM-085-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -200C, -
300, -400, and -500 Series Airplanes

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

ACTION: Notice of proposed rulemaking (NPRM).

-----------------------------------------------------------------------

SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD)
for certain Boeing Model 737-100, -200, -200C, -300, -400, and -500
series airplanes. This proposed AD would require doing repetitive
internal eddy current and detailed inspections to detect cracked
stringer tie clips; doing applicable corrective and related
investigative actions, if necessary; and measuring the fastener spacing
and the edge margin; as applicable. As a temporary alternative to doing
the actions described previously, this proposed AD would require
repetitive external general visual inspections of the skin and lap
joints for cracks and evidence of overload resulting from cracked
stringer tie clips, and applicable corrective actions if necessary.
This proposed AD results from a report of several cracked stringer tie
clips. We are proposing this AD to prevent multiple cracked stringer
tie clips and damaged skin and frames, which could lead to the skin and
frame structure developing cracks and consequent decompression of the
airplane.

DATES: We must receive comments on this proposed AD by November 5,
2007.

ADDRESSES: Use one of the following addresses to submit comments on
this proposed AD.

[[Page 53707]]

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: 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-
29255; Directorate Identifier 2007-NM-085-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

We have received a report of 15 cracked stringer tie clips in the
crown skin area between station (STA) 500B and STA 907 between stringer
(S) 10L and S-10R, on a Boeing Model 737 airplane. The airplane had
accumulated total 31,415 flight cycles. This airplane had three
adjacent cracked clips at two consecutive body station frames (six
clips total). The six stringer tie clips were cracked along the joint
common to the stringer. The six total stringer tie clips were the same
formed bonded stringer tie clips that were installed as terminating
action in accordance with Boeing Service Bulletin 737-53-1085, Revision
1, dated May 10, 1990.
Stringer tie clip cracking along the joint common to the stringer
occurs primarily as a result of cyclic loading associated with cabin
pressure and flight loads. If three adjacent stringer tie clips on one
frame crack, it could result in an inability of the fuselage frame
structure to support operating loads. This could result in local skin
buckling and deformation of the skin and frame. Multiple cracked
stringer tie clips and damaged skin and frames, if not corrected, could
lead to the skin and frame structure developing cracks, which could
result in decompression of the airplane.

Other Relevant Rulemaking

We previously issued AD 93-08-04, amendment 39-8551 (58 FR 25546,
April 27, 1993), for certain Boeing Model 737-100, -200, and -200C
series airplanes. That AD requires structural inspections of older
airplanes and is part of the Aging Airplane Service Bulletin Structural
Modification and Inspection Program. Boeing Service Bulletin 737-53-
1085, Revision 1, is one of several service bulletins required by that
AD.
This proposed AD would affect the requirements of AD 93-08-04
pertaining to Boeing Service Bulletin 737-53-1085, Revision 1.
We previously issued AD 2002-07-08, amendment 39-12702 (67 FR
17917, April 12, 2002), applicable to certain Boeing Model 737-200, -
200C, -300, -400, and -500 series airplanes. That AD 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
cracking found. That AD also requires modification of the fuselage lap
joints at certain locations, which constitutes terminating action for
certain repetitive inspections.
This proposed AD would not affect the current requirements of AD
2002-07-08.

Relevant Service Information

We have reviewed Boeing Special Attention Service Bulletin 737-53-
1268, dated August 25, 2006. This service bulletin supersedes Boeing
Service Bulletin 737-53-1085, Revision 1.
The service bulletin describes one required inspection and one
temporary alternative inspection. Inspection A, the one required
inspection, involves the following:
Doing repetitive internal eddy current and detailed
inspections to detect cracked stringer tie clips. The inspection area
is from STA 559 to STA 887, STA 360 to STA 540, and STA 907. The
inspections from STA 559 to STA 887 are identical to those specified in
Boeing Service Bulletin 737-53-1085, Revision 1. If the terminating
action was done in accordance with Boeing Service Bulletin 737-53-1085,
the inspections need to be restarted in accordance with Boeing Special
Attention Service Bulletin 737-53-1268.
Doing applicable corrective and related investigative
actions, if necessary. The corrective actions include replacing any
cracked stringer tie clip with a new clip, contacting Boeing for repair
instructions, and repairing any damaged lap joints; as applicable. The
related investigative actions include doing an internal detailed
inspection to detect damaged or deformed skin and frame and to detect
damaged lap joints, and doing internal eddy current inspections to
detect cracked lap joints; as applicable.
Measuring the fastener spacing and the edge margin; as
applicable.
The initial compliance time for Inspection A is before the
accumulation of 25,000 or 35,000 total flight cycles (as applicable),
or within 2 or 3 years (as applicable) after the date of the service
bulletin, whichever occurs later. The repeat interval for Inspection A
is 15,000 or 20,000 flight cycles (as applicable).

[[Page 53708]]

Inspection B, which is a temporary alternative to doing Inspection
A, involves the following:
Doing repetitive external general visual inspections of
the skin and lap joints for cracks and evidence of overload resulting
from cracked stringer tie clips, and
Doing applicable corrective actions if necessary. The
corrective actions include contacting Boeing for repair instructions,
and repairing any cracked or damaged lap joint and skin.
For Inspection B, the threshold for the initial compliance times
ranges between 37,500 and 47,500 total flight cycles, and the grace
period for the initial compliance times is 25,000 flight cycles or 6 or
12 months, depending on the number of flight cycles on the airplane.
Inspection B must be done before exceeding an inspection period ranging
from 5,000 to 50,000 total flight cycles. The repeat interval for
Inspection B is 2,500 flight cycles.
The service bulletin also describes procedures for an optional eddy
current inspection to detect damaged stringer tie clips and replacement
of any cracked clip with a new clip. The optional inspection can be
done in addition to and at the same time as Inspection A described
previously. The optional inspection will detect damaged stringer clips
earlier than the detailed inspection, which may prevent future costly
repairs.
Accomplishing the actions specified in the service information is
intended to adequately address the unsafe condition.
The service bulletin refers to Boeing Service Bulletin 737-53A1177,
Revision 6, dated May 31, 2001, as an additional source of service
information for doing an internal eddy current inspection of the lap
joint for certain airplane configurations.

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, except as discussed under
``Differences Between the Proposed AD and Service Information.''

Differences Between the Proposed AD and Service Information

The service information specifies to contact the manufacturer for
instructions on how to repair certain conditions, but this proposed AD
would require repairing those conditions in one of the following ways:
Using a method that we approve; or
Using data that meet the certification basis of the
airplane, and that have been approved by an Authorized Representative
for the Boeing Commercial Airplanes Delegation Option Authorization
Organization whom we have authorized to make those findings.

Costs of Compliance

There are about 2,685 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 \1\ Average labor Cost per registered Fleet cost \1\
rate per hour airplane \1\ airplanes
----------------------------------------------------------------------------------------------------------------
Inspection A................. Between 40 and $80 Between $3,200 787 Between
103. and $8,240, $2,518,400 and
per inspection $6,484,880,
cycle. per inspection
cycle.
Inspection B (temporary Between 2 and 80 Between $160 787 Between
alternative to Inspection A). 109. and $8,720. $125,920 and
$6,862,640,
per inspection
cycle.
----------------------------------------------------------------------------------------------------------------
\1\ Depending on the airplane configuration.

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.

[[Page 53709]]

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-2007-29255; Directorate Identifier 2007-NM-
085-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by November
5, 2007.

Affected ADs

(b) AD 93-08-04, amendment 39-8551.

Applicability

(c) This AD applies to Boeing Model 737-100, -200, -200C, -300,
-400, and -500 series airplanes, certificated in any category; as
identified in Boeing Service Bulletin 737-53-1268, dated August 25,
2006.

Unsafe Condition

(d) This AD results from a report of several cracked stringer
tie clips. We are issuing this AD to prevent multiple cracked
stringer tie clips and damaged skin and frames, which could lead to
the skin and frame structure developing cracks and consequent
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 References

(f) The term ``the service bulletin,'' as used in this AD, means
the Accomplishment Instructions of Boeing Service Bulletin 737-53-
1268, dated August 25, 2006.

Inspection A: Required Internal Inspections, Applicable Corrective and
Related Investigative Actions, and Measurement

(g) Do repetitive internal eddy current and detailed inspections
to detect cracked stringer tie clips; do applicable corrective and
related investigative actions, if necessary; and measure the
fastener spacing and the edge margin; as applicable. Do all
applicable actions at the applicable compliance times and repeat
intervals identified in tables 2 through 8 inclusive of paragraph
1.E., ``Compliance,'' of the service bulletin; except as provided by
paragraphs (i), (j), and (k) of this AD. Do all applicable actions
in accordance with the Accomplishment Instructions of the service
bulletin, except as provided by paragraph (m) of this AD.

Note 1: The service bulletin refers to Boeing Service Bulletin
737-53A1177, Revision 6, dated May 31, 2001, as an additional source
of service information for doing an internal eddy current inspection
of the lap joint for certain airplane configurations.

Inspection B: Temporary Alternative External Inspections and Corrective
Actions

(h) As a temporary alternative to doing the actions required by
paragraph (g) of this AD, do repetitive external general visual
inspections of the skin and lap joints for cracks and evidence of
overload resulting from cracked stringer tie clips, and applicable
corrective actions if necessary. Do all applicable actions at the
applicable compliance times and repeat intervals identified in
tables 9 through 12 inclusive of paragraph 1.E., ``Compliance,'' of
the service bulletin, but not to exceed the flight cycles in the
``Inspection Period Allowed'' column of the tables; except as
provided by paragraphs (i) and (l) of this AD. Do all applicable
actions in accordance with the Accomplishment Instructions of the
service bulletin, except as provided by paragraph (m) of this AD.

Note 2: The eddy current inspection along the stringer tie clip
radius to detect damage and replacement, as applicable, specified in
paragraph 3.B.5. of the Accomplishment Instructions of the service
bulletin are not required by this AD. The actions are optional and
can be done in addition to and at the same time as the actions
required by paragraph (g) of this AD.

Exceptions to Service Information

(i) Where the service bulletin specifies a compliance time after
the date of the service bulletin, this AD requires compliance within
the specified compliance time after the effective date of this AD.
(j) For Model 737-100, -200, and -200C series airplanes, on
which Boeing Service Bulletin 737-53-1085, Revision 1, dated May 10,
1990, has not been done in accordance with AD 93-08-04: As of the
effective date of this AD, do the applicable inspections from STA
559 to STA 887 in accordance with paragraph (g) of this AD, at the
applicable compliance times specified in paragraph (b) of AD 93-08-
04.
(k) In the first row of tables 5 and 6 of paragraph 1.E.,
``Compliance,'' of the service bulletin, where the service bulletin
specifies a compliance time of before 25,000 total airplane flight
cycles, this AD requires a compliance time of before the
accumulation of 25,000 total flight cycles, or within 2 years after
the effective date of this AD, whichever occurs later.
(l) Where the service bulletin specifies no starting point
(e.g., ``after the date on the service bulletin'') for a grace
period, this AD requires compliance within the specified grace
period after the effective date of this AD.
(m) Where the service bulletin specifies to contact Boeing for
appropriate action: Before further flight, repair the discrepancy
using a method approved in accordance with the procedures specified
in paragraph (o) of this AD.

Certain Actions End Certain Requirements of AD 93-08-04

(n) Accomplishment of the internal eddy current and detailed
inspections for STA 559 to STA 887 in accordance with paragraph (g)
of this AD constitutes compliance with the inspections required by
paragraph (a) of AD 93-08-04, as it pertains to Boeing Service
Bulletin 737-53-1085, Revision 1, dated May 10, 1990. Accomplishment
of the internal eddy current and detailed inspections does not
terminate the remaining requirements of AD 93-08-04, as it applies
to other service bulletins. Operators are required to continue to
inspect and/or modify per the other service bulletins listed in that
AD.

Alternative Methods of Compliance (AMOCs)

(o)(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 September 12, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. E7-18554 Filed 9-19-07; 8:45 am]

BILLING CODE 4910-13-P