7-3 report of 18 inch crack in fuselage skin

[Federal Register: April 24, 2008 (Volume 73, Number 80)]
[Proposed Rules]
[Page 22088-22090]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr24ap08-9]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2008-0412; Directorate Identifier 2007-NM-346-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 supersede an existing airworthiness
directive (AD) that applies to all Boeing Model 737-300, -400, and -500
series airplanes. The existing AD currently requires repetitive
inspections for discrepancies of the fuselage skin under the dorsal fin
assembly, and repairing if necessary. This proposed AD would require an
inspection for any chafing or crack in the fuselage skin and abrasion
resistant coating at the dorsal fin landing, an inspection for damage
to the dorsal fin seals, attach clip, and seal retainer, and other
specified and corrective actions as necessary. The new proposed
requirements would end the need for the existing repetitive
inspections. This proposed AD results from a report of an 18-inch crack
found in the fuselage skin area under the blade seals of the nose cap
of the dorsal fin due to previous wear damage, and additional reports
of fuselage skin wear. We are proposing this AD to prevent
discrepancies of the fuselage skin, which could result in fatigue
cracking due to cabin pressurization and consequent rapid in-flight
decompression of the airplane fuselage.

DATES: We must receive comments on this proposed AD by June 9, 2008.

ADDRESSES: You may send comments by any of the following methods:
Federal eRulemaking Portal: Go to http://
www.regulations.gov. Follow the instructions for submitting comments.
Fax: 202-493-2251.
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.
Hand Delivery: U.S. Department of Transportation, Docket
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New
Jersey Avenue, SE., Washington, DC 20590, between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal holidays.
For service information identified in this AD, contact Boeing
Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207.

Examining the AD Docket

You may examine the AD docket on the Internet at http://
www.regulations.gov; or in person at the Docket Management Facility
between 9 a.m. and 5 p.m., Monday through Friday, except Federal
holidays. The AD docket contains this proposed AD, the regulatory
evaluation, any comments received, and other information. The street
address for the Docket Office (telephone 800-647-5527) is in the
ADDRESSES section. Comments will be available in the AD docket shortly
after receipt.

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 send any written relevant data, views, or
arguments about this proposed AD. Send your comments to an address
listed under the ADDRESSES section. Include ``Docket No. FAA-2008-0412;
Directorate Identifier 2007-NM-346-AD'' at the beginning of your
comments. We specifically invite comments on the overall regulatory,
economic, environmental, and energy aspects of this proposed AD. We
will consider all comments received by the closing date and may amend
this proposed AD because of those comments.
We will post all comments we receive, without change, to http://
www.regulations.gov, including any personal information you provide. We
will also post a report summarizing each substantive verbal contact we
receive about this proposed AD.

Discussion

On October 18, 2004, we issued AD 2004-22-05, amendment 39-13833
(69 FR 62567, October 27, 2004), for all Boeing Model 737-300, -400,
and -500 series airplanes. That AD requires inspecting for
discrepancies of the fuselage skin under the dorsal fin assembly, and
repairing if necessary. That AD resulted from a report of an 18-inch
crack found in the fuselage skin area under the blade seals of the nose
cap of the dorsal fin due to previous wear damage. We issued that AD to
find and fix discrepancies of the fuselage skin, which could result in
fatigue cracking due to cabin pressurization, and consequent rapid in-
flight decompression of the airplane fuselage.

Actions Since Existing AD Was Issued

Since we issued AD 2004-22-05, we have received additional reports
of fuselage skin wear found during routine maintenance inspections and
accomplishment of Boeing Service Bulletin 737-55-1057, dated December
12, 1996, and Revision 1, dated July 22, 1999. (Revision 1 of Boeing
Service Bulletin 737-55-1057 was cited as an additional source of
service information for inspecting for discrepancies of the fuselage
skin under the dorsal fin assembly.) As a result, the manufacturer has
developed a new corrective action and terminating action to adequately
address the unsafe condition.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 737-53A1266, dated
August 30, 2007. The service bulletin describes procedures for doing a
detailed inspection for any chafing or crack in the fuselage skin and
abrasion resistant coating at the dorsal fin landing and a detailed
inspection for damage to the dorsal fin seals, attach clip, and seal
retainer.
The service bulletin also describes procedures for doing other
specified and corrective actions as necessary. The other specified
action is to install wear strips if no skin wear is found during the
inspection. The corrective actions include (1) replacing the dorsal fin
seals with new seals if any damaged seal is found, (2) replacing the
seal retainers

[[Page 22089]]

and attach clip with new parts, if any damaged retainers or clips are
found, or if they have not been installed in accordance with Boeing
Service Bulletin 737-55-1057, and (3) repairing the fuselage skin if
any crack or damage is found. For certain airplanes, the repair
includes contacting Boeing for repair instructions, installing wear
strips, or repairing as given in the structural repair manual, as
applicable. For certain other airplanes, the repair includes removing
any previously installed repair doubler and repairing as given in the
applicable structural repair manual, ensuring that the previous repairs
did not have countersunk fasteners that knife edged the skin, doing a
high frequency eddy current inspection of the outer row fasteners for
any eye-brow or hole crack and repairing as applicable, ensuring that
fastener spacing and size are within the acceptable limits, and
extending the new repair doubler a minimum of two fastener rows beyond
the critical row of the outer fastener row of the previous repair.
Accomplishing the actions specified in the service information is
intended to adequately address the unsafe condition.
The service bulletin specifies that the detailed inspection and
other specified action be done within 18,000 flight cycles or 72
months, whichever occurs later. For certain airplanes, the service
bulletin specifies that the removal of the previously installed repair
doubler and the repair be done within 18,000 flight cycles or 72
months, whichever occurs later. The service bulletin also specifies
that the corrective actions be done before further flight.

FAA's Determination and Requirements of the Proposed AD

We have evaluated all pertinent information and identified an
unsafe condition that is likely to develop on other airplanes of the
same type design. For this reason, we are proposing this AD, which
would supersede AD 2004-22-05 and would retain the requirements of the
existing AD. This proposed AD would also require accomplishing the
actions specified in service information described previously, except
as discussed under ``Difference Between the Proposed AD and Service
Bulletin.'' The new proposed requirements would end the need for the
existing repetitive inspections.

Difference Between the Proposed AD and Service Bulletin

The service bulletin 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.

Change to Existing AD

Boeing Commercial Airplanes has received a Delegation Option
Authorization (DOA). We have revised paragraph (g) of this AD to
delegate the authority to approve an alternative method of compliance
for any repair required by this AD to an Authorized Representative for
the Boeing Commercial Airplanes DOA rather than a Designated
Engineering Representative (DER).

Costs of Compliance

There are about 1,963 airplanes of the affected design in the
worldwide fleet. This proposed AD would affect about 627 airplanes of
U.S. registry.
The actions that are required by AD 2004-22-05 and retained in this
proposed AD take about 2 work hours per airplane, at an average labor
rate of $80 per work hour. Based on these figures, the estimated cost
of the currently required actions for U.S. operators is $100,320, or
$160 per airplane, per inspection cycle.
The new proposed actions would take about 15 work hours per
airplane, at an average labor rate of $80 per work hour. Required parts
would cost about $801 per airplane. Based on these figures, the
estimated cost of the new actions specified in this proposed AD for
U.S. operators is $1,254,627, or $2,001 per airplane.

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
removing amendment 39-13833 (69 FR 62567, October 27, 2004) and adding
the following new airworthiness directive (AD):

Boeing: Docket No. FAA-2008-0412; Directorate Identifier 2007-NM-
346-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by June 9,
2008.

Affected ADs

(b) This AD supersedes AD 2004-22-05.

[[Page 22090]]

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 an 18-inch crack found in
the fuselage skin area under the blade seals of the nose cap of the
dorsal fin due to previous wear damage, and additional reports of
fuselage skin wear. We are issuing this AD to prevent discrepancies
of the fuselage skin, which could result in fatigue cracking due to
cabin pressurization and consequent rapid in-flight decompression of
the airplane fuselage.

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.

Restatement of Requirements of AD 2004-22-05

Repetitive Detailed Inspections

(f) For airplanes specified in either paragraph (f)(1), (f)(2),
(f)(3), or (f)(4) of this AD: Accomplish a detailed inspection for
discrepancies (wear or cracking) of the fuselage skin under the
dorsal fin assembly by doing all the actions specified in Boeing
Message Number 1-QXO35, dated October 13, 2004. Repeat the
inspection thereafter at intervals not to exceed 9,000 flight
cycles. Accomplishing all of the applicable actions specified in
paragraph (i) of this AD terminates the repetitive inspections
required by this paragraph.

Note 1: For the purposes of this AD, a detailed inspection is:
``An intensive examination of a specific item, installation, or
assembly to detect damage, failure, or irregularity. Available
lighting is normally supplemented with a direct source of good
lighting at an intensity deemed appropriate. Inspection aids such as
mirror, magnifying lenses, etc., may be necessary. Surface cleaning
and elaborate procedures may be required.''

(1) For airplanes with line numbers 1001 through 2828 inclusive
that have not been inspected as of November 12, 2004 (the effective
date of AD 2004-22-05), in accordance with Boeing Service Bulletin
737-55-1057, dated December 12, 1996; or Revision 1, dated July 22,
1999: Inspect before the accumulation of 18,000 total flight cycles,
or within 90 days after November 12, 2004, whichever is later.
(2) For airplanes with line numbers 2829 through 3132 inclusive
that are not included in the effectivity of Boeing Service Bulletin
737-55-1057, dated December 12, 1996; or Revision 1, dated July 22,
1999: Inspect before the accumulation of 18,000 total flight cycles,
or within 90 days after November 12, 2004, whichever is later.
(3) For airplanes with line numbers 1001 through 2828 inclusive
that have been inspected, but not repaired or modified as of the
effective date of this AD, in accordance with Boeing Service
Bulletin 737-55-1057, dated December 12, 1996; or Revision 1, dated
July 22, 1999: Inspect within 9,000 flight cycles after
accomplishing the inspection, or within 90 days after November 12,
2004, whichever is later.
(4) For airplanes with line numbers 1001 through 2828 inclusive
that have been inspected and repaired or modified as of the
effective date of this AD, in accordance with Boeing Service
Bulletin 737-55-1057, dated December 12, 1996; or Revision 1, dated
July 22, 1999: Inspect within 18,000 flight cycles after
accomplishing the repair or modification, or within 90 days after
November 12, 2004, whichever is later; and if a repair doubler is
installed, before further flight, inspect the repair doubler for
discrepancies (wear or cracking).

Note 2: Boeing Message Number 1-QXO35, dated October 13, 2004,
references Part I of Boeing Service Bulletin 737-55-1057, Revision
1, dated July 22, 1999, as an additional source of service
information for accomplishing the actions required by paragraph (f)
of this AD.

Repair

(g) If any discrepancy (wear or cracking) is found during any
inspection required by paragraph (f) of this AD, before further
flight, repair in accordance with a method approved by the Manager,
Seattle Aircraft Certification Office (ACO), FAA; or using a method
approved in accordance with the procedures specified in paragraph
(1) of this AD.

Reporting Not Required

(h) Although Boeing Message Number 1-QXO35, dated October 13,
2004, specifies to report any fuselage skin cracking found during
the detailed inspections, this AD does not include that requirement.

New Requirements of This AD

New Inspections and Other Specified and Corrective Actions

(i) At the applicable compliance times specified in paragraph
1.E. of Boeing Alert Service Bulletin 737-53A1266, dated August 30,
2007, except as provided by paragraph (j) of this AD: Do a detailed
inspection for any chafing or crack in the fuselage skin of the
dorsal fin landing and abrasion resistant coating, do a detailed
inspection for damage to dorsal fin seals, attach clip, and seal
retainer, and do all the applicable other specified and corrective
actions, by accomplishing all of the applicable actions specified in
the Accomplishment Instructions of the service bulletin, except as
provided by paragraph (k) of this AD. Accomplishing all of the
applicable actions specified in this paragraph terminates the
repetitive inspections required by paragraph (f) of this AD.

Exception to Compliance Times

(j) Where Boeing Alert Service Bulletin 737-53A1266, dated
August 30, 2007, specifies counting the compliance time from ``* * *
the date on the service bulletin,'' this AD requires counting the
compliance time from the effective date of this AD.

Exception to Corrective Actions

(k) If any damage is found aft of body station 908 during any
inspection required by this AD, and Boeing Alert Service Bulletin
737-53A1266, dated August 30, 2007, specifies to contact Boeing for
appropriate action: Before further flight, repair the fuselage skin
using a method approved in accordance with the procedures specified
in paragraph (l) of this AD.

Alternative Methods of Compliance (AMOCs)

(l)(1) The Manager, Seattle Aircraft Certification Office,
Transport Airplane Directorate, 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.
(4) AMOCs approved previously in accordance with AD 2004-22-05
are approved as AMOCs for the corresponding provisions of paragraphs
(f) and (g) of this AD.

Issued in Renton, Washington, on April 15, 2008.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. E8-8913 Filed 4-23-08; 8:45 am]

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