[Federal Register Volume 72, Number 50 (Thursday, March 15, 2007)]
[Proposed Rules]
[Pages 12136-12140]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E7-4738]



[[Page 12136]]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2007-27525; Directorate Identifier 2006-NM-159-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 747-100, 747-100B, 747-
100B SUD, 747-200B, 747-200C, 747-300, 747-400, 747-400D, 747SR, and 
747SP 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 certain Boeing Model 747 airplanes. The 
existing AD currently requires repetitive inspections to detect cracks 
and/or corrosion of the girt bar support fitting at certain main entry 
doors (MED), and repair or replacement of the support fitting. The 
existing AD also provides for various terminating actions for the 
repetitive inspections. This proposed AD would require the following 
additional actions: An inspection, for certain airplanes, for correct 
installation of square and conical washers in the girt bar support 
fitting; an inspection, for certain other airplanes, to determine if 
the washers are installed; and related investigative and corrective 
action if necessary. This proposed AD results from a report that the 
square and conical washers may be installed incorrectly in the girt bar 
support fitting on airplanes on which the support fitting was repaired 
or replaced in accordance with the requirements of the existing AD. We 
are proposing this AD to detect and correct corrosion of the girt bar 
support fitting, which could result in separation of the escape slide 
from the lower door sill during deployment, and subsequently prevent 
proper operation of the escape slides at the main entry doors during an 
emergency. We are also proposing this AD to detect and correct 
incorrect installation of the square and conical washers in the girt 
bar support fitting, which could result in failure of the escape slide 
when deployed.

DATES: We must receive comments on this proposed AD by April 30, 2007.

ADDRESSES: Use one of the following addresses to submit comments on 
this proposed AD.
    <bullet> DOT Docket Web site: Go to http://dms.dot.gov and follow 
the instructions for sending your comments electronically.
    <bullet> Government-wide rulemaking Web site: Go to http://www.regulations.gov and follow the instructions for sending your 
comments electronically.
    <bullet> Mail: Docket Management Facility; U.S. Department of 
Transportation, 400 Seventh Street SW., Nassif Building, room PL-401, 
Washington, DC 20590.
    <bullet> Fax: (202) 493-2251.
    <bullet> 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 service information identified in this 
proposed AD.

FOR FURTHER INFORMATION CONTACT: Patrick Gillespie, Aerospace Engineer, 
Cabin Safety and Environmental Systems Branch, ANM-150S, FAA, Seattle 
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98057-3356; telephone (425) 917-6429; 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 ``Docket No. 
FAA-2007-27525; Directorate Identifier 2006-NM-159-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 the 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

    On October 31, 1996, we issued AD 96-23-05, amendment 39-9810 (61 
FR 58318, November 14, 1996), for certain Boeing Model 747 series 
airplanes. That AD requires repetitive inspections to detect cracks 
and/or corrosion of the girt bar support fitting at certain main entry 
doors (MED); and repair or replacement of the support fitting. That AD 
also provides for various terminating actions for the repetitive 
inspections. That AD resulted from reports that, during scheduled 
deployment tests of main entry door slides, corrosion was found on the 
floor structure supports for the escape slides of the main deck entry 
doors on these airplanes. We issued that AD to prevent such corrosion, 
which could result in separation of the escape slide from the lower 
door sill during deployment, and subsequently prevent proper operation 
of the escape slides at the main entry doors during an emergency.

Actions Since Existing AD Was Issued

    Since we issued AD 96-23-05, Boeing has determined that the square 
and conical washers may be installed incorrectly in the girt bar 
support fitting on airplanes on which the support fitting was repaired 
or replaced in accordance with Boeing Service Bulletin 747-53A2378, 
dated June 24, 1993; Revision 1, dated March 10, 1994; or Revision 2, 
dated July 24, 2003 (Revision 1 of the service bulletin was referenced 
as the appropriate source of service information for doing the actions 
specified in AD 96-23-05).

Relevant Service Information

    We have reviewed Boeing Service Bulletin 747-53A2378, Revision 3, 
dated August 11, 2005. The service bulletin contains essentially the 
same procedures for the actions described in the earlier revisions of 
the service bulletin, but Revision 3 revises the procedures for the 
installation of the square and conical washers on the girt bar support 
fitting.

[[Page 12137]]

    Revision 3 also adds actions for airplanes on which the support 
fitting was replaced or repaired in accordance with any earlier 
revision of the service bulletin:
    <bullet> For Groups 7, 8, and 9 airplanes identified in the service 
bulletin: Do an inspection for correct installation of square and 
conical washers in the girt bar floor fitting, related investigative 
action, and corrective actions. The related investigative action is an 
inspection of the bolts and washers for damage. The corrective actions 
include installing the square and conical washers correctly and 
contacting the manufacturer if damage is found.
    <bullet> For Groups 1 through 6 airplanes identified in the service 
bulletin: Do an inspection to check if square and conical washers are 
installed in the girt bar floor fitting, related investigative actions, 
and corrective actions. The related investigative actions include doing 
an inspection for correct installation of square and conical washers in 
the girt bar floor fitting and an inspection of the bolts and washers 
for damage. The corrective actions include installing the square and 
conical washers correctly and contacting the manufacturer if damage is 
found.
    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 develop on other airplanes of the 
same type design. For this reason, we are proposing this AD, which 
would supersede AD 96-23-05 and would retain the requirements of the 
existing AD. This proposed AD would also require the following actions 
for airplanes on which the support fitting was repaired or replaced in 
accordance with Boeing Service Bulletin 747-53A2378, dated June 24, 
1993; Revision 1, dated March 10, 1994; or Revision 2, dated July 24, 
2003: An inspection, for certain airplanes, for correct installation of 
square and conical washers in the girt bar support fitting; an 
inspection, for certain other airplanes, to determine if the washers 
are installed; and related investigative and corrective action if 
necessary.

Differences Between the Proposed AD and the Service Bulletin

    Although Boeing Service Bulletin 747-53A2378 specifies that 
operators may contact the manufacturer if certain damage is found, this 
proposed AD would require operators to repair those conditions using a 
method approved by the FAA.
    Although Boeing Service Bulletin 747-53A2378, Revision 3, specifies 
doing certain actions if Boeing Service Bulletin 747-53A2378, dated 
June 24, 1993; Revision 1, dated March 10, 1994; or Revision 2, dated 
July 24, 2003; was accomplished, this proposed AD would require those 
actions to also be done if Boeing Service Bulletin 747-25A2831, dated 
August 29, 1991, was accomplished. Paragraph (m) of AD 96-23-05 allows 
installation of the girt bar fitting in accordance with Boeing Service 
Bulletin 747-25A2831 as an acceptable method of compliance. Therefore, 
installations done in accordance with Boeing Service Bulletin 747-
25A2831 should also be inspected for incorrect installation of the 
square and conical washers in the girt bar support fitting.

Change to Existing AD

    This proposed AD would retain all requirements of AD 96-23-05. 
Since AD 96-23-05 was issued, the AD format has been revised, and 
certain paragraphs have been rearranged. As a result, the corresponding 
paragraph identifiers have changed in this proposed AD, as listed in 
the following table:

                      Revised Paragraph Identifiers
------------------------------------------------------------------------
                                             Corresponding  requirement
        Requirement in AD 96-23-05              in this  proposed AD
------------------------------------------------------------------------
Note 1....................................  paragraph (f).
paragraph (a).............................  paragraph (g).
paragraph (b).............................  paragraph (h).
paragraph (c).............................  paragraph (i).
paragraph (d).............................  paragraph (j).
paragraph (e).............................  paragraph (k).
paragraph (f).............................  paragraph (l).
paragraph (g).............................  paragraph (m).
paragraph (h).............................  paragraph (n).
paragraph (i).............................  paragraph (o).
paragraph (j).............................  paragraph (p).
paragraph (k).............................  paragraph (q).
paragraph (l).............................  paragraph (r).
paragraph (m).............................  paragraph (s).
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    Note 2 and paragraph (o) of AD 96-23-05 have been removed from this 
proposed AD. On July 10, 2002, the FAA issued a new version of 14 CFR 
part 39 (67 FR 47997, July 22, 2002), which governs the FAA's 
airworthiness directives system. The regulation now includes material 
that relates to altered products and alternative methods of compliance 
(AMOCs), as well as special flight permits (e.g., ferry flights).

Clarification of Doors Affected by the Proposed AD

    We have also revised Note 1 of AD 96-23-05, which has the 
corresponding requirement in paragraph (f) of this proposed AD. We have 
added the statement ``the requirements of this AD are also not 
applicable to doors on airplanes converted to an all-cargo 
configuration.''

Explanation of Change to Applicability

    We have revised the applicability of the existing AD to identify 
model designations as published in the most recent type certificate 
data sheet for the affected models. Special freighters are not 
identified in the type certificate data sheet so the phrase ``special 
freighters'' has been removed from the applicability. However, as 
stated previously, we have added a statement to exempt doors on 
airplanes converted to an all-cargo configuration.

Explanation of Change Made to Existing Requirements

    We have changed all references to a ``detailed visual inspection'' 
in the existing AD to ``detailed inspection'' in this proposed AD.

Clarification of Alternative Method of Compliance (AMOC) Paragraph

    We have revised this action to clarify the appropriate procedure 
for notifying the principal inspector before using any approved AMOC on 
any airplane to which the AMOC applies.

Costs of Compliance

    There are about 1,012 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. The average labor rate 
per hour is $80. The cost varies depending on the configuration of the 
airplane.

[[Page 12138]]



                                                 Estimated Costs
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                                                                            Number of U.S.-
             Action                   Work hours       Cost per airplane      registered          Fleet cost
                                                                               airplanes
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Inspection of MEDs (required by   Between 88 and 102  Between $7,040 and  169...............  Between $1,189,760
 AD 96-23-05).                                         $8,160, per                             and $1,379,040,
                                                       inspection cycle.                       per inspection
                                                                                               cycle.
Inspection for correct            6.................  $480..............  Up to 169.........  Up to $81,120.
 installation (new proposed
 action).
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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 
removing amendment 39-9810 (61 FR 58318, November 14, 1996) and adding 
the following new airworthiness directive (AD):

Boeing: Docket No. FAA-2007-27525; Directorate Identifier 2006-NM-
159-AD.

Comments Due Date

    (a) The FAA must receive comments on this AD action by April 30, 
2007.

Affected ADs

    (b) This AD supersedes AD 96-23-05.

Applicability

    (c) This AD applies to Boeing Model 747-100, 747-100B, 747-100B 
SUD, 747-200B, 747-200C, 747-300, 747-400, 747-400D, 747SR, and 
747SP series airplanes, certificated in any category, line numbers 1 
through 868 inclusive.

Unsafe Condition

    (d) This AD results from reports that, during scheduled 
deployment tests of main entry door slides, corrosion was found on 
the floor structure supports for the escape slides of the main deck 
entry doors on these airplanes. This AD also results from a report 
that the square and conical washers may be installed incorrectly in 
the girt bar support fitting on airplanes on which the support 
fitting was repaired or replaced in accordance with the requirements 
of AD 96-23-05. We are issuing this AD to detect and correct 
corrosion of the girt bar support fitting, which could result in 
separation of the escape slide from the lower door sill during 
deployment, and subsequently prevent proper operation of the escape 
slides at the main entry doors during an emergency. We are also 
issuing this AD to detect and correct incorrect installation of the 
square and conical washers in the girt bar support fitting, which 
could result in failure of the escape slide when deployed.

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 96-23-05 With New Service Information

Doors Exempt From/Affected by This AD

    (f) The requirements of this AD are not applicable to doors 
where an escape slide or slide/raft is not installed or is not used 
for passenger egress (such as a deactivated door 3, at doors 4 and/
or 5 of an airplane being operated in the ``combi'' configuration, 
or any door not used for passenger egress in a ``convertible'' (an 
airplane configured for quick change from passenger to cargo)). The 
requirements of this AD are also not applicable to doors on 
airplanes converted to an all-cargo configuration. The requirements 
of this AD become applicable at the time when an escape slide or 
slide/raft is installed on such doors, or when such doors are 
activated and/or converted for passenger use. The requirements also 
become applicable at the time an airplane operating in an all-cargo 
configuration is converted to a passenger or passenger/cargo 
configuration.

Inspections and Corrective Actions for Airplanes Equipped With Main 
Entry Door (MED) 1

    (g) For airplanes equipped with MED 1: Prior to the accumulation 
of 16 years of service since date of manufacture of the airplane, or 
within 18 months after December 16, 1996 (the effective date of AD 
96-23-05), whichever occurs later, perform a detailed inspection to 
detect cracking and/or corrosion of the girt bar support fitting at 
the left and right MED 1, in accordance with Boeing Service Bulletin 
747-53A2378, Revision 1, dated March 10, 1994; or Boeing Service 
Bulletin 747-53A2378, Revision 3, dated August 11, 2005. After the 
effective date of this AD, only Revision 3 may be used.
    (h) If no cracking or corrosion is found during the inspection 
required by paragraph (g) of this AD, prior to further flight, 
accomplish either paragraph (h)(1) or (h)(2) of this AD, in 
accordance with the applicable instructions specified in Boeing 
Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994; or 
Boeing Service Bulletin

[[Page 12139]]

747-53A2378, Revision 3, dated August 11, 2005. After the effective 
date of this AD, only Revision 3 may be used.
    (1) Install a new fitting with new fasteners, and reinstall the 
threshold assembly with new corrosion-resistant fasteners, in 
accordance with the service bulletin. After these actions are 
accomplished, no further action is required by paragraph (h) of this 
AD; or
    (2) Reinstall the threshold assembly with corrosion-resistant 
fasteners, in accordance with the service bulletin. Thereafter, 
repeat the inspection required by paragraph (g) of this AD at 
intervals not to exceed 6 years.
    (i) If any cracking is found during the inspection required by 
paragraph (g) or (h)(2) of this AD, prior to further flight, install 
a new fitting with new fasteners, and reinstall the threshold 
assembly with new corrosion-resistant fasteners, in accordance with 
Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 
1994; or Boeing Service Bulletin 747-53A2378, Revision 3, dated 
August 11, 2005. After the effective date of this AD, only Revision 
3 may be used. After these actions are accomplished, no further 
action is required by this paragraph.
    (j) If any corrosion is found during the inspection required by 
paragraph (g) or (h)(2) of this AD, prior to further flight, 
accomplish either paragraph (j)(1) or (j)(2) of this AD, in 
accordance with Boeing Service Bulletin 747-53A2378, Revision 1, 
dated March 10, 1994; or Boeing Service Bulletin 747-53A2378, 
Revision 3, dated August 11, 2005. After the effective date of this 
AD, only Revision 3 may be used.
    (1) Install a new fitting with new fasteners, and reinstall the 
threshold assembly with new corrosion-resistant fasteners in 
accordance with the service bulletin. After these actions are 
accomplished, no further action is required by this paragraph; or
    (2) Blend out corrosion in accordance with the service bulletin.
    (i) If blend out of corrosion is beyond 10 percent of original 
thickness or any crack is found during accomplishment of the blend 
out procedures, install a new fitting with new fasteners, and 
reinstall the threshold assembly with new corrosion-resistant 
fasteners, in accordance with the service bulletin. After these 
actions are accomplished, no further action is required by this 
paragraph.
    (ii) If blend out of corrosion does not exceed 10 percent of 
original material thickness, accomplish either paragraph 
(j)(2)(ii)(A) or (j)(2)(ii)(B) of this AD:
    (A) Install a new fitting with new fasteners, and reinstall 
threshold assembly with new corrosion-resistant fasteners, in 
accordance with the service bulletin. After these actions are 
accomplished, no further action is required by this paragraph; or
    (B) Install the repaired fitting with new fasteners and 
reinstall the threshold assembly with corrosion-resistant fasteners, 
in accordance with the service bulletin. Thereafter, repeat the 
inspection and applicable corrective actions required by paragraph 
(g) of this AD at intervals not to exceed 6 years.

Inspections and Corrective Actions for Airplanes Equipped With MED 
2, 4, and/or 5 (MED 2, 3, and/or 4 on Model 747SP Series Airplanes)

    (k) For airplanes equipped with MED 2, 4, and/or 5 (MED 2, 3, 
and/or 4 on Model 747SP series airplanes): Prior to the accumulation 
of 10 years of service since date of manufacture of the airplane, or 
within 18 months after December 16, 1996, whichever occurs later, 
perform a detailed inspection to detect cracking and/or corrosion of 
the girt bar support fitting at the left and right MED 2, 4, and 5 
(MED 2, 3, and 4 on Model 747SP series airplanes), in accordance 
with Boeing Service Bulletin 747-53A2378, Revision 1, dated March 
10, 1994; or Boeing Service Bulletin 747-53A2378, Revision 3, dated 
August 11, 2005. After the effective date of this AD, only Revision 
3 may be used.
    (l) If no cracking or corrosion is found during the inspection 
required by paragraph (k) of this AD, prior to further flight, 
accomplish either paragraph (l)(1) or (l)(2) of this AD, in 
accordance with the applicable instructions in Boeing Service 
Bulletin 747-53A2378, Revision 1, dated March 10, 1994; or Boeing 
Service Bulletin 747-53A2378, Revision 3, dated August 11, 2005. 
After the effective date of this AD, only Revision 3 may be used.
    (1) Remove the inspected fitting and reinstall it with a new 
coat of primer and new fasteners; and reinstall the threshold 
assembly with new corrosion-resistant fasteners; in accordance with 
the service bulletin. After these actions are accomplished, no 
further action is required by this paragraph; or
    (2) Reinstall the serrated plate assembly and the girt bar floor 
fitting with corrosion-resistant fasteners, in accordance with the 
service bulletin. Thereafter, repeat the inspection required by 
paragraph (k) of this AD at intervals not to exceed 6 years.
    (m) If any cracking is found during the inspection required by 
paragraph (k) or (l)(2) of this AD, prior to further flight, install 
a new fitting with new fasteners, and reinstall the threshold 
assembly with new corrosion-resistant fasteners, in accordance with 
Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 
1994; or Boeing Service Bulletin 747-53A2378, Revision 3, dated 
August 11, 2005. After the effective date of this AD, only Revision 
3 may be used. After these actions are accomplished, no further 
action is required by this paragraph.
    (n) If any corrosion is found during the inspection required by 
paragraph (k) or (l)(2) of this AD, prior to further flight, 
accomplish either paragraph (n)(1) or (n)(2) of this AD, in 
accordance with Boeing Service Bulletin 747-53A2378, Revision 1, 
dated March 10, 1994; or Boeing Service Bulletin 747-53A2378, 
Revision 3, dated August 11, 2005. After the effective date of this 
AD, only Revision 3 may be used.
    (1) Install a new fitting with new fasteners, and reinstall the 
threshold assembly with new corrosion-resistant fasteners, in 
accordance with the service bulletin. After these actions are 
accomplished, no further action is required by this paragraph; or
    (2) Blend out corrosion in accordance with the service bulletin.
    (i) If blend out of corrosion is beyond 10 percent of original 
thickness or any crack is found during accomplishment of the blend 
out procedures, install a new fitting with new fasteners, and 
reinstall the threshold assembly with new corrosion-resistant 
fasteners, in accordance with the service bulletin. After these 
actions are accomplished, no further action is required by this 
paragraph.
    (ii) If blend out of corrosion does not exceed 10 percent of 
original material thickness, install the repaired fitting with new 
fasteners, and reinstall the threshold assembly with new corrosion-
resistant fasteners, in accordance with the service bulletin. After 
these actions are accomplished, no further action is required by 
this paragraph.
    (o) For airplanes equipped with main entry door (MED) 3 (this 
paragraph does not apply to Model 747SP series airplanes): Prior to 
the accumulation of 16 years of service since date of manufacture of 
the airplane, or within 18 months after December 16, 1996, whichever 
occurs later, perform a detailed inspection to detect cracking and/
or corrosion of the girt bar support angles at the left and right 
MED 3, in accordance with Boeing Service Bulletin 747-53A2378, 
Revision 1, dated March 10, 1994; or Boeing Service Bulletin 747-
53A2378, Revision 3, dated August 11, 2005. After the effective date 
of this AD, only Revision 3 may be used.
    (p) If no cracking or corrosion is found during the inspection 
required by paragraph (o) of this AD, prior to further flight, 
accomplish either paragraph (p)(1) or (p)(2) of this AD in 
accordance with the applicable instructions in Boeing Service 
Bulletin 747-53A2378, Revision 1, dated March 10, 1994; or Boeing 
Service Bulletin 747-53A2378, Revision 3, dated August 11, 2005. 
After the effective date of this AD, only Revision 3 may be used.
    (1) Remove the inspected angle and reinstall it with a new coat 
of primer and new fasteners; and reinstall the threshold assembly 
with new corrosion-resistant fasteners; in accordance with the 
service bulletin. After these actions are accomplished, no further 
action is required by this paragraph; or
    (2) Reinstall the corner scuff plate and the threshold apron 
with corrosion-resistant fasteners, in accordance with the service 
bulletin. Thereafter, repeat the inspection required by paragraph 
(o) of this AD at intervals not to exceed 6 years.
    (q) If any crack common to the support angles is found during 
the inspection required by paragraph (o) or (p)(2) of this AD, prior 
to further flight, accomplish the actions specified in paragraph 
(q)(1) or (q)(2), as applicable, in accordance with Boeing Service 
Bulletin 747-53A2378, Revision 1, dated March 10, 1994; or Boeing 
Service Bulletin 747-53A2378, Revision 3, dated August 11, 2005. 
After the effective date of this AD, only Revision 3 may be used:
    (1) Install the new angles with new fasteners, and reinstall the 
threshold assembly with new corrosion-resistant fasteners. After 
these actions are accomplished, no further action is required by 
this paragraph of this AD; or

[[Page 12140]]

    (2) For any cracking found only in the corner casting as 
specified in the service bulletin, accomplish either paragraph 
(q)(2)(i) or (q)(2)(ii) prior to further flight:
    (i) Replace the corner casting in accordance with the service 
bulletin; or
    (ii) Repair the cracked part in accordance with a method 
approved by the Manager, Seattle Aircraft Certification Office 
(ACO), FAA, Transport Airplane Directorate. Refer to paragraph (w) 
of this AD for the appropriate procedure for seeking such an 
approval. (This option is provided in order to give operators time 
to obtain a replacement corner casing without grounding an 
airplane.) This repair is considered temporary action only; 
replacement of the corner casting eventually must be accomplished in 
accordance with a schedule prescribed by the Manager, Seattle ACO.
    (r) If any corrosion is found during the inspection required by 
paragraph (o) of this AD, prior to further flight, accomplish either 
paragraph (r)(1) or (r)(2) of this AD, in accordance with Boeing 
Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994; or 
Boeing Service Bulletin 747-53A2378, Revision 3, dated August 11, 
2005. After the effective date of this AD, only Revision 3 may be 
used.
    (1) Install the new angles with new fasteners, and reinstall the 
threshold assembly with new corrosion-resistant fasteners, in 
accordance with the service bulletin. After these actions are 
accomplished, no further action is required by this paragraph; or
    (2) Blend out corrosion in accordance with the service bulletin.
    (i) If blend out of corrosion is beyond 10 percent of original 
thickness, or if any crack common to the support angles is found 
during accomplishment of the blend out procedures, install the new 
angles with new fasteners, and reinstall the threshold assembly with 
new corrosion-resistant fasteners, in accordance with the service 
bulletin. After these actions are accomplished, no further action is 
required by this paragraph.
    (ii) If blend out of corrosion does not exceed 10 percent of 
original material thickness, install the repaired angles with new 
fasteners, and reinstall the threshold assembly with new corrosion-
resistant fasteners, in accordance with the service bulletin. After 
these actions are accomplished, no further action is required by 
this paragraph.

Actions Accomplished According to Previous Issue of Service 
Bulletin

    (s) Installation of a girt bar support fitting in accordance 
with Boeing Service Bulletin 747-25A2831, dated August 29, 1991, 
before the effective date of this AD, is considered acceptable for 
compliance with the corresponding requirements of paragraphs (h), 
(i), (j), (l), (m), and (n) of this AD for each affected fitting 
location.

New Requirements of This AD

Inspections for the Washers and Related Investigative/Corrective 
Actions

    (t) For Groups 7, 8, and 9 airplanes identified in Boeing 
Service Bulletin 747-53A2378, Revision 3, dated August 11, 2005, on 
which the support fitting was replaced or repaired in accordance 
with Boeing Service Bulletin 747-53A2378, dated June 24, 1993; 
Revision 1, dated March 10, 1994; or Revision 2, dated July 24, 
2003; or Boeing Service Bulletin 747-25A2831, dated August 29, 1991: 
Within 18 months after the effective date of this AD, do a general 
visual inspection for correct installation of square and conical 
washers in the girt bar floor fittings, and, before further flight, 
do all applicable related investigative and corrective actions. Do 
all actions in accordance with Figure 18 and the applicable steps 
specified on page 52 of the Accomplishment Instructions of Boeing 
Service Bulletin 747-53A2378, Revision 3, dated August 11, 2005, 
except as provided by paragraph (v) of this AD.
    (u) For Groups 1 through 6 airplanes identified in Boeing 
Service Bulletin 747-53A2378, Revision 3, dated August 11, 2005, on 
which the support fitting was replaced or repaired in accordance 
with Boeing Service Bulletin 747-53A2378, dated June 24, 1993; 
Revision 1, dated March 10, 1994; or Revision 2, dated July 24, 
2003; or with Boeing Service Bulletin 747-25A2831, dated August 29, 
1991: Within 18 months after the effective date of this AD, do a 
general visual inspection to determine if square and conical washers 
are installed in the girt bar floor fittings, and before further 
flight, do all applicable related investigative and corrective 
actions. Do all actions in accordance with Figure 18 and the 
applicable steps specified on pages 52 and 53 of the Accomplishment 
Instructions of Boeing Service Bulletin 747-53A2378, Revision 3, 
dated August 11, 2005, except as provided by paragraph (v) of this 
AD.
    (v) If any damage is found during any inspection required by 
paragraphs (t) and (u) of this AD, and the bulletin specifies 
contacting Boeing for appropriate action: Before further flight, do 
the repair using a method approved by the Manager, Seattle ACO, FAA, 
or in accordance with data meeting the certification basis of the 
airplane approved by an Authorized Representative for the Boeing 
Commercial Airplanes Delegation Option Authorization 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.

Alternative Methods of Compliance (AMOCs)

    (w)(1) The Manager, Seattle 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) Before using any AMOC approved in accordance with Sec.  
39.19 on any airplane to which the AMOC applies, notify the 
appropriate principal inspector in the FAA Flight Standards 
Certificate Holding District Office.
    (3) AMOCs approved previously in accordance with AD 96-23-05, 
are approved as AMOCs for the corresponding provisions of this AD.

    Issued in Renton, Washington, on March 7, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
 [FR Doc. E7-4738 Filed 3-14-07; 8:45 am]
BILLING CODE 4910-13-P