[Federal Register Volume 71, Number 186 (Tuesday, September 26, 2006)]
[Proposed Rules]
[Pages 56064-56070]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 06-8232]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2004-19755; Directorate Identifier 2004-NM-23-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 747 Airplanes

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

ACTION: Supplemental notice of proposed rulemaking (NPRM); reopening of 
comment period.

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SUMMARY: The FAA is revising an earlier proposed airworthiness 
directive (AD) for certain Boeing Model 747 airplanes. The original 
NPRM would have required repetitive tests to detect hot air leaking 
from the trim air diffuser ducts or sidewall riser duct assemblies 
(collectively referred to in this proposed AD as ``TADDs''), related 
investigative actions, and corrective actions if necessary. The 
original NPRM also would have provided an optional terminating action 
for the repetitive tests. The original NPRM resulted from reports of 
sealant deteriorating on the outside of the center wing fuel tank and 
analysis that sealant may deteriorate inside the tank due to excess 
heat from leaking TADDs. This action revises the original NPRM by 
referring to improved inspection procedures and extending the 
repetitive interval for certain related investigative actions. We are 
proposing this supplemental NPRM to prevent leakage of fuel or fuel 
vapors into areas where ignition sources may be present, which could 
result in a fire or explosion.

DATES: We must receive comments on this supplemental NPRM by October 
23, 2006.

ADDRESSES: Use one of the following addresses to submit comments on 
this supplemental NPRM.
    <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: Dan Kinney, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification 
Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone 
(425) 917-6499; fax (425) 917-6590.

SUPPLEMENTARY INFORMATION:

Comments Invited

    We invite you to submit any relevant written data, views, or 
arguments regarding this supplemental NPRM. Send your comments to an 
address listed in the ADDRESSES section. Include the docket number 
``Docket No. FAA-2004-19755; Directorate Identifier 2004-NM-23-AD'' at 
the beginning of your comments. We specifically invite comments on the 
overall regulatory, economic, environmental, and energy aspects of this 
supplemental NPRM. We will consider all comments received by the 
closing date and may amend this supplemental NPRM in light of those 
comments.
    We will post all comments submitted, 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 supplemental NPRM. 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 in the Nassif Building at the DOT 
street address stated in ADDRESSES. Comments will be available in the 
AD docket shortly after the Docket Management System receives them.

[[Page 56065]]

Discussion

    We proposed to amend 14 CFR part 39 with a notice of proposed 
rulemaking (NPRM) for an AD (the ``original NPRM'') for certain Boeing 
Model 747 airplanes. The original NPRM was published in the Federal 
Register on December 1, 2004 (69 FR 69844). The original NPRM proposed 
to require repetitive tests to detect hot air leaking from the trim air 
diffuser ducts or sidewall riser duct assemblies (collectively referred 
to in this supplemental NPRM as ``TADDs''), related investigative 
actions, and corrective actions if necessary. The original NPRM also 
would have provided an optional terminating action for the repetitive 
tests.

Actions Since Original NPRM Was Issued

    Since we issued the original NPRM, we have received reports 
indicating that the procedures referenced in Boeing Alert Service 
Bulletin 747-21A2418, Revision 2, dated March 4, 2004 (which we 
referenced in the original NPRM as the applicable source of service 
information for the proposed actions), are not sufficient to detect a 
damaged TADD in a timely manner.

Relevant Service Information

    We have reviewed Boeing Service Bulletin 747-21A2418, Revision 4, 
dated November 17, 2005. Revision 4 of the service bulletin describes 
procedures that are similar to those in Revision 2. However, Revision 4 
revises the part numbers for certain improved sidewall riser duct 
assemblies for installation on Boeing Model 747-400 series airplanes 
that are not freighters. This change is due to new environmental and 
flammability-resistance standards required under amendments 25-110, 91-
279, 121-301, 125-43, and 135-90 of the Federal Aviation Regulations. 
(Refer to the final rule, docket no. FAA-2000-7909, ``Improved 
Flammability Standards for Thermal/Acoustic Insulation Materials Used 
in Transport Category Airplanes'' (68 FR 45046, July 31, 2003; with 
corrections published 68 FR 50054, August 20, 2003; and 69 FR 6532, 
February 11, 2004).) Revision 4 of the service bulletin also recommends 
increasing the initial inspection threshold from 27,000 flight hours to 
32,000 flight hours, and the repetitive inspection interval from 7,000 
flight hours to 12,000 flight hours, for the general visual inspection 
for damage or discrepancies of the TADDs.
    Certain changes to the service information that were originally 
introduced in Boeing Service Bulletin 747-21A2418, Revision 3, dated 
December 21, 2004, are retained in Revision 4 of the service bulletin:
    <bullet> Chapter 21-61-20 of the airplane maintenance manual (AMM) 
has been revised to contain more definitive pass/fail criteria for the 
repetitive tests and inspections of the TADDs. These revised criteria 
increase the chances of a defective TADD being detected in a timely 
manner.
    <bullet> Chapter 21-61-21 of the AMM contains procedures for 
unwrapping insulation blankets as necessary before the general visual 
inspection to detect defective TADDs is done on Boeing Model 747-400 
non-freighter series airplanes.
    Accomplishing the actions specified in Revision 4 of the service 
information is intended to adequately address the unsafe condition. We 
have revised paragraphs (f), (g), (h), and (j) and Note 2 of this 
supplemental NPRM to refer to Revision 4 of the service information. We 
have also added a new paragraph (k) to this supplemental NPRM, and re-
identified the subsequent paragraph, to give credit for actions done 
before the effective date of the AD in accordance with previous issues 
of the service bulletin.
    With regard to extending compliance times for the general visual 
inspection, we have revised Table 1 of this supplemental NPRM to extend 
the repetitive interval for the general visual inspections from 7,000 
flight hours to 12,000 flight hours. We have also revised Table 1 of 
this supplemental NPRM to extend the initial compliance threshold from 
27,000 total flight hours to 32,000 total flight hours.

Comments

    We have considered the following comments on the original NPRM.

Request To Relieve Testing Requirement

    British Airways requests that we revise paragraph (f) of the 
original NPRM to relieve operators of the requirement to do a test to 
detect hot air leaking from the TADDs at the same time as the general 
visual inspection for damage or discrepancies of the TADDs. The 
commenter notes that, if the inspection is being accomplished, there is 
no need to do the test during the same maintenance check. The commenter 
assumes that the inspection exceeds the intent of the test in that the 
inspection would detect discrepancies of the TADDs that the test may 
not.
    We concur with the commenter's request. We agree that it would be 
redundant to perform a hot air leak test at the same time as the 
general visual inspection when the repetitive intervals for these 
actions coincide. Therefore, we have revised paragraph (f) of this 
supplemental NPRM to clarify that, when the compliance times for a hot 
air leak test and a general visual inspection coincide, the hot air 
leak test is not required at that time.

Request To Allow Installation of Serviceable Improved TADDs

    The Air Transport Association (ATA), on behalf of its member 
Northwest Airlines (NWA), and Boeing request that we revise paragraphs 
(h) and (j) and Note 3 of the original NPRM to allow installation of 
serviceable improved TADDs. Boeing states that the improved TADDs are 
expected to hold up well in service, and its customers are concerned 
about the proposed restriction on installing serviceable TADDs. In its 
comment submitted through ATA, NWA states that it does not believe that 
the failure rate of new TADDs is a significant improvement over 
properly repaired or serviceable used TADDs. NWA states that only a 
very small percentage of high-time TADDS have failed in service, and it 
believes that all duct leaks will be sufficiently addressed by the 
repetitive tests and inspections proposed in the original NPRM. NWA 
also disagrees that the TADDs deteriorate at a known rate in service, 
which was the justification stated in the original NPRM for not 
allowing installation of used TADDs. Similarly, Boeing comments that 
the deterioration rate is highly variable.
    We agree with the commenters' request to allow installing 
serviceable improved TADDs. Our intent was to prohibit installing used 
ducts of the old type, not used ducts of the improved type. We have 
determined that installing serviceable improved parts will provide an 
acceptable level of safety. We have revised paragraphs (h) and (j) of 
this supplemental NPRM accordingly, and we have omitted Note 3 from 
this supplemental NPRM. However, as mentioned in the discussion of New 
Relevant Service Information, improved flammability standards may 
prohibit installing certain new, improved TADDs on non-freighter 
airplanes. Subsequent to the publication of the original NPRM, some of 
the improved TADDs failed a test of their insulation that is required 
by the improved flammability standards. Thus, under the requirements of 
that rule, certain improved TADDs that were listed in revisions of 
Boeing Service Bulletin 747-21A2418 prior to Revision 4, can no longer 
be installed (although they need not be removed if they were

[[Page 56066]]

installed prior to September 2, 2003, the effective date of FAA-2000-
7909).
    Also, we do not agree with the commenters' statements that the rate 
of deterioration is unknown, although we acknowledge that there are 
many variables that contribute to the deterioration of the TADDs. The 
rate of deterioration is known to the extent that we know that TADDs 
having accumulated more than 20,000 total flight hours are suspect. 
Also, we do not know of an inspection process that would be adequate to 
ensure the integrity of a used duct of the old material. For these 
reasons, we have determined that it is not appropriate to allow 
installation of used TADDs made of the old material.

Request To Remove References to Deteriorated Sealant

    Boeing requests that we revise the original NPRM to remove 
references to ``reports of deteriorating sealants both inside and 
outside the center wing fuel tank due to heat damage from leaking 
TADDs.'' Boeing states that it is not aware of reports of damaged fuel 
tanks caused by leaking TADDs.
    We agree to revise the statement of what prompted the proposed AD 
to remove the references to reports of deterioration of the sealant 
inside the center wing fuel tank. We are unable to confirm direct 
observation of primary seal deterioration.
    However, we disagree that primary or secondary seal deterioration 
is unlikely. Following reports of TADD leaks, Boeing analyzed the 
temperatures that the primary (inside) and secondary (outside) fuel 
barriers could reach. Analysis revealed that the secondary barrier 
could reach temperatures between 300 [deg]F and 450 [deg]F, and that 
internal tank temperatures could reach 378 [deg]F. The sealants are not 
effective above 325 [deg]F and are not qualified for prolonged exposure 
above 160 [deg]F. In addition, FAA personnel observed deterioration of 
the secondary sealant in the center wing fuel tank. Therefore, if any 
damage or discrepancy of a TADD is found, we find it necessary to 
require a general visual inspection for damage of the primary and 
secondary fuel barriers of the center wing tank, and adjacent areas and 
items, as specified in paragraph (h) of this supplemental NPRM.
    Based on this information, we have revised the Summary of this 
supplemental NPRM to state that the original NPRM ``resulted from 
reports of sealant deteriorating on the outside of the center wing fuel 
tank and analysis that sealant may deteriorate inside the tank due to 
excess heat from leaking TADDs.'' We have similarly revised paragraph 
(d) of this supplemental NPRM.

Request To Require Inspections Only on Affected Side

    ATA, on behalf of NWA, requests that we revise paragraph (h) of the 
original NPRM to require an inspection for damage of the fuel barriers 
and adjacent areas only on the side of the airplane where a TADD 
failed. In its comment submitted through ATA, NWA states that the 
original NPRM does not acknowledge that the TADDs are located on both 
the left and right sides of the airplane. Neither ATA nor NWA state a 
justification for the request.
    We infer that the commenter's request is intended to reduce the 
amount of work that needs to be accomplished to allow a quicker return 
of the airplane to service. We agree that it would be acceptable to 
inspect the fuel barriers and adjacent areas only on the side of the 
airplane where a TADD failed if no damage is found on the side of the 
airplane where a TADD failed. However, if any damage of the fuel 
barriers or adjacent areas is found on the side of the airplane where a 
TADD failed, both sides of the airplane must be inspected. Both sides 
must be inspected because the barrier damage is caused by hot air and 
if there is damage to one side, then there may be enough leakage to 
damage the other side.
    We have revised paragraph (h)(1) of this AD to state that, ``If no 
damage is found on the side of the airplane where the damaged or 
discrepant TADD is found, inspecting the other side of the airplane is 
not required.''
    In addition, we have revised paragraph (j) of this AD to clarify 
the specific circumstances under which tests and inspections required 
by paragraph (f) of this AD are terminated. These changes better 
acknowledge that, as the commenter points out, there are TADDs on both 
the left and right sides of the airplane.

Request To Revise Repetitive Inspection Intervals

    KLM Royal Dutch Airlines (KLM) requests that we extend the 
repetitive interval for the hot air leak test specified in paragraph 
(f)(1) of the original NPRM from 1,200 flight hours to 1,600 flight 
hours. The commenter states that the repetitive interval of 1,200 
flight hours is not consistent with its maintenance intervals. KLM 
explains that its A-check is 770 flight hours, so it would have to 
perform this test either every A-check or in between A-checks. KLM 
states that either alternative would result in excessive cost. KLM 
notes that a repetitive interval of 1,600 flight hours would allow it 
to perform the test every second A-check. Boeing also commented that 
the interval for the hot air leak test should coincide with actual A-
check intervals.
    We do not agree with the request to extend the repetitive interval 
for the hot air leak test. The extension of the repetitive interval for 
the general visual inspections to 12,000 flight hours, as discussed 
previously, is contingent on the repetitive hot air leak tests being 
performed at intervals not to exceed 1,200 flight hours. We find that 
this repetitive interval is necessary to ensure that any discrepant 
TADD will be detected in a timely manner. We note that the 1,200-
flight-hour repetitive interval is consistent with Boeing's 
recommendation in Revision 4 of the service bulletin and in its re-
evaluation of compliance times. Further, since maintenance schedules 
vary among operators, it is not possible for us to revise the 
repetitive interval to meet the needs of a specific operator. In 
developing an appropriate repetitive interval for this action, we 
considered the manufacturer's recommendation, the degree of urgency 
associated with the subject unsafe condition, the average utilization 
of the affected fleet, and the time necessary to perform the test 
(estimated at 3 work hours). In light of all of these factors, we find 
that 1,200 flight hours is an appropriate interval of time for affected 
airplanes to continue to operate between repetitive tests without 
compromising safety. We have not changed the supplemental NPRM in this 
regard. However, paragraph (l) of the supplemental NPRM provides 
operators the opportunity to request an extension of the compliance 
time if data are presented to justify such an extension.

Request To Revise Compliance Time for Inspection of Replaced TADDs

    ATA, on behalf of NWA, suggests that we revise the compliance time 
for the general visual inspection for damaged or replaced TADDs made of 
the original material. Paragraph (i) of the original NPRM specifies a 
compliance time of 27,000 flight hours after the TADD is replaced for 
this inspection. The commenter suggests that this compliance time be 
revised to ``the next C-check after 21,200 flight hours.''
    We partially agree with this request. We do not agree with the 
request to state the compliance time in relation to a C-check. We find 
that such a non-specific compliance time would not ensure that damaged 
TADDs are detected in a timely manner. However, we agree to extend the 
compliance time for inspecting replaced TADDs from 27,000

[[Page 56067]]

flight hours to 32,000 flight hours after replacement. We note that 
affected operators may elect to do the general visual inspection of the 
TADDs earlier than the stated compliance time, if it is more convenient 
to their maintenance schedules. We have revised paragraph (i) of this 
supplemental NPRM accordingly.

Request To Revise Compliance Time for Initial Leak Test

    ATA, on behalf of NWA, requests that we revise the compliance time 
for the initial test specified in paragraph (f)(1) of the original 
NPRM. NWA states support for the test but believes that an equivalent 
level of safety can be achieved by doing the initial test at the 
compliance time specified in the referenced service bulletin, which the 
commenter interprets as 180 days or 2,000 hours, whichever is first. 
NWA states that a failed duct is often detected when floorboards or 
sidewalls become hot, or when the airplane crew has difficulty 
controlling cabin temperatures. Thus, a failed duct is often corrected 
by normal maintenance practices that limit exposure to high 
temperatures. For this reason, NWA states that compliance time for the 
initial inspection recommended in the service bulletin is sufficient to 
detect duct leaks that are not detected during normal operations.
    We do not agree with the commenter's request. We note that 180 days 
or 2,000 flight hours (whichever is first) is the compliance time 
recommended by the referenced service bulletin for airplanes with 
20,000 or more total flight hours. However, as we explained in the 
``Differences Between the Proposed AD and Service Information'' section 
of the original NPRM, the compliance threshold of 21,200 total flight 
hours is the equivalent of the inspection threshold of 20,000 total 
flight hours specified in the service bulletin, plus one repeat 
interval (1,200 flight hours). In addition, the manufacturer has not 
requested that we revise the compliance time proposed in the original 
NPRM. In developing an appropriate compliance time for the initial 
test, we considered the manufacturer's recommendation, and the degree 
of urgency associated with the subject unsafe condition. In light of 
these factors, we find that the compliance time of 21,200 total flight 
hours, or 1,200 flight hours after the effective date of the AD, 
whichever is later, represents an appropriate interval of time for 
affected airplanes to continue to operate without compromising safety. 
We have not changed the supplemental NPRM in this regard.

Request To Ensure Adequate Supply of Replacement Parts

    Lufthansa requests that we ensure that an adequate supply of 
replacement parts will be available for operators to comply with the 
proposed requirements. The commenter notes that there have been delays 
in obtaining material for planned modifications in accordance with 
Boeing Service Bulletin 747-21A2418. The commenter states that it 
anticipates that it will find TADDs that must be replaced.
    We acknowledge the commenter's concerns and the delays it 
experienced. Parts availability is one of the factors that we consider 
when establishing a compliance time for an AD. In this case, we have 
determined through the manufacturer that an adequate supply of 
replacement parts will be available for operators to accomplish the 
proposed requirements within the proposed compliance time. We find that 
no additional changes to the supplemental NPRM are needed in this 
regard.

Request To Clarify Requirements of Paragraph (h)

    Boeing requests that we revise paragraph (h) of the original NPRM 
to state that the actions in that paragraph apply if any discrepancy is 
found during either the hot air leak test or the general visual 
inspection for damage in accordance with paragraph (f) of the original 
NPRM.
    We contacted Boeing for clarification of the meaning and intent of 
its comment. Upon further review of paragraph (h) of the original NPRM, 
Boeing concluded its comment was not necessary and could be withdrawn. 
We have not changed the supplemental NPRM in this regard.

Request To Allow Use of Later Revisions of Service Information

    Air New Zealand (ANZ) requests that we revise paragraph (j) of the 
original NPRM, Optional Terminating Action, to allow use of later 
revisions of the referenced service information. ANZ notes that, when 
the AD refers to a specific revision of the service bulletin, e.g., 
Revision 2, operators may not use the later revisions without being out 
of compliance with the requirements of the AD when new service 
information is released that contains new part numbers for equivalent 
or better parts. ANZ suggests that we include language referring to 
``any subsequent documents, which list a new or equivalent part number 
or better, that does not have this unsafe condition.''
    We do not agree with the request to refer to later revisions of the 
service information that have not yet been released. (As explained 
previously, we have revised this supplemental NPRM to refer to Boeing 
Service Bulletin 747-21A2418, Revision 4.) When we refer to a specific 
service bulletin in an AD, using a phrase such as that suggested by the 
commenter, or a phrase like ``or later FAA-approved revisions,'' 
violates Office of the Federal Register regulations for approving 
materials that are incorporated by reference. However, affected 
operators may request approval to use a later revision of the 
referenced service bulletin as an alternative method of compliance, 
under the provisions of paragraph (l) of this supplemental NPRM. We 
have not changed the supplemental NPRM further in this regard.

Request To Revise Cost Impact

    Qantas Airways (QANTAS) requests that we revise the cost impact 
stated in the original NPRM. The commenter believes that the original 
NPRM underestimates the number of work hours necessary to do the 
general visual inspection for damage or discrepancies of the TADDs. 
QANTAS notes that significant time is necessary to gain access to the 
TADDs to perform the inspection and to close up after the inspection, 
in addition to testing the in-seat entertainment equipment. The 
commenter notes that the estimate of 43 work hours in Boeing Service 
Bulletin 747-21A2418 is more realistic.
    We do not agree. The cost analysis in AD rulemaking actions 
typically does not include incidental costs such as the time required 
to gain access and close up, time necessary for planning, or time 
necessitated by other administrative actions. Those incidental costs, 
which may vary significantly among operators, are almost impossible to 
calculate. We have not changed the supplemental NPRM in this regard.

Requests for Editorial Changes

    Boeing requests that we revise the Relevant Service Information 
section of the original NPRM as follows:
    <bullet> Revise the statement, ``The related investigative actions 
are repetitive general visual inspections for discrepancies or damage 
of the TADDs* * * '' to also refer to the hot air leak tests as related 
investigative actions.
    <bullet> Revise the statement, ``After a TADD is replaced with a 
new, improved TADD, the repetitive inspections are no longer needed for 
that TADD,'' to note that neither the repetitive leak tests nor the 
repetitive inspections are needed after a new, improved TADD is 
installed.

[[Page 56068]]

    Boeing's rationale for the first change is that the statement in 
the original NPRM implies that only the visual inspections constitute 
valid investigative actions. Boeing's rationale for the second change 
is to avoid questions (from operators) and misinterpretation.
    We acknowledge the commenter's requests. However, we do not agree 
that any change is necessary. The Relevant Service Information section 
of the original NPRM states that the referenced service bulletin 
``describes procedures for repetitive tests to detect hot air leaking 
from the TADDs, related investigative actions, and corrective actions 
if necessary.'' The statement to which the commenter refers defines 
what we mean by ``related investigative actions.'' We find that the 
contents of the Relevant Service Information section are sufficiently 
clear as written in the original NPRM. With regard to the commenter's 
second item, we agree with the statement as revised by the commenter. 
However, the Relevant Service Information section of the original NPRM 
is not restated in this supplemental NPRM. Thus, no change is possible 
in this regard.

Explanation of Additional Changes

    We have reduced the estimated number of airplanes that would be 
affected by this supplemental NPRM to be consistent with the number of 
airplanes identified in the service bulletin.
    After the original NPRM was issued, we reviewed the figures we have 
used over the past several years to calculate AD costs to operators. To 
account for various inflationary costs in the airline industry, we find 
it necessary to increase the labor rate used in these calculations from 
$65 per work hour to $80 per work hour. The cost impact information, 
below, reflects this increase in the specified hourly labor rate.
    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.

FAA's Determination and Proposed Requirements of the Supplemental NPRM

    Certain changes discussed above expand the scope of the original 
NPRM; therefore, we have determined that it is necessary to reopen the 
comment period to provide additional opportunity for public comment on 
this supplemental NPRM.

Costs of Compliance

    There are about 1,081 airplanes of the affected design in the 
worldwide fleet. The following table provides the estimated costs for 
U.S. operators to comply with this supplemental NPRM.

                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                              Number  of
                                    Work      Average                            U.S.-
             Action                hours    labor rate    Cost per airplane   registered         Fleet cost
                                             per hour                          airplanes
----------------------------------------------------------------------------------------------------------------
Hot air leak test...............        3           $80  $240, per test               216  $51,840, per test
                                                          cycle.                            cycle.
General visual inspection.......        5            80  400, per                     216  86,400, per
                                                          inspection cycle.                 inspection cycle.
----------------------------------------------------------------------------------------------------------------

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 supplemental NPRM 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-2004-19755; Directorate Identifier 2004-NM-
23-AD.

Comments Due Date

    (a) The FAA must receive comments on this AD action by October 
23, 2006.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Boeing Model 747-100, 747-100B, 747-100B 
SUD, 747-200B,

[[Page 56069]]

747-200C, 747-200F, 747-300, 747-400, 747-400D, 747-400F, 747SR, and 
747SP series airplanes; certificated in any category; line numbers 1 
through 1316 inclusive.

Unsafe Condition

    (d) This AD results from reports of sealant deteriorating on the 
outside of the center wing fuel tank and analysis that sealant may 
deteriorate inside the tank due to excess heat from leaking trim air 
diffuser ducts or sidewall riser duct assemblies (collectively 
referred to in this AD as ``TADDs''). We are issuing this AD to 
prevent leakage of fuel or fuel vapors into areas where ignition 
sources may be present, which could result in a fire or explosion.

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.

Repetitive Tests and Inspections

    (f) Do the actions in Table 1 of this AD at the times specified 
in Table 1 of this AD, in accordance with the Accomplishment 
Instructions of Boeing Service Bulletin 747-21A2418, Revision 4, 
dated November 17, 2005. When the compliance times for a hot air 
leak test and a general visual inspection coincide, the hot air leak 
test is not required at that time, but is required within 1,200 
flight hours (i.e., one repeat interval) after the general visual 
inspection.

                                           Table 1.--Compliance Times
----------------------------------------------------------------------------------------------------------------
                                                                              Then repeat within this interval
            Do this action--                Initially at the later of--        until paragraph (j) is done--
----------------------------------------------------------------------------------------------------------------
(1) Repetitive test to detect hot air      Prior to the accumulation of    1,200 flight hours.
 leaking from TADDs.                       21,200 total flight hours, or
                                           within 1,200 flight hours
                                           after the effective date of
                                           this AD.
(2) General visual inspection for damage  Prior to the accumulation of     12,000 flight hours.
 or discrepancies of the TADDs.            32,000 total flight hours, or
                                           within 12,000 flight hours
                                           after the effective date of
                                           this AD, except as provided by
                                           paragraph (g) of this AD.
----------------------------------------------------------------------------------------------------------------


    Note 1: For the purposes of this AD, a general visual inspection 
is: ``A visual examination of an interior or exterior area, 
installation, or assembly to detect obvious damage, failure, or 
irregularity. This level of inspection is made from within touching 
distance unless otherwise specified. A mirror may be necessary to 
ensure visual access to all surfaces in the inspection area. This 
level of inspection is made under normally available lighting 
conditions such as daylight, hangar lighting, flashlight, or 
droplight and may require removal or opening of access panels or 
doors. Stands, ladders, or platforms may be required to gain 
proximity to the area being checked.''


    Note 2: Boeing Service Bulletin 747-21A2418, Revision 4, refers 
to Chapters 21-61-20 and 21-61-21 of the 747 Airplane Maintenance 
Manual as an additional source for service information for the test 
and inspections of the TADDs.

    (g) If any hot air leak is found during any test required by 
paragraph (f) of this AD: Before further flight, do the general 
visual inspection for damage or discrepancies of the TADDs, in 
accordance with the Accomplishment Instructions of Boeing Service 
Bulletin 747-21A2418, Revision 4, dated November 17, 2005.

Corrective Actions

    (h) If any damage or discrepancy is found during any general 
visual inspection for damage required by paragraph (f) or (g) of 
this AD: Do the actions in paragraphs (h)(1), (h)(2), (h)(3), and 
(h)(4) of this AD, as applicable. Do all of these actions in 
accordance with the Accomplishment Instructions of Boeing Service 
Bulletin 747-21A2418, Revision 4, dated November 17, 2005.
    (1) Before further flight: Perform a general visual inspection 
for damage of the primary and secondary fuel barriers of the center 
wing tank; structure adjacent to the discrepant TADD; and cables, 
cable pulleys, and raised cable seals in the over-wing area. If no 
damage is found on the side of the airplane where the damaged or 
discrepant TADD is found, inspecting the other side of the airplane 
is not required.
    (2) Before further flight: Repair all damage or discrepancies 
found.
    (3) Before further flight: Replace any damaged TADD with a new 
TADD having the same part number or a new or serviceable, improved 
TADD having a part number listed in the ``New TADD Part Number'' or 
``New Sidewall Riser Duct Assy Part Number'' column, as applicable, 
of the tables in Section 2.C.2. of the service bulletin.
    (4) Repeat the test and inspection required by paragraph (f) of 
this AD at the times specified in Table 1 of this AD, except as 
provided by paragraphs (i) and (j) of this AD.
    (i) For any original-material TADD that is replaced with a new 
TADD having the same part number as the TADD being replaced: Within 
21,200 flight hours after the TADD is replaced, do the test to 
detect hot air leaking from the replaced TADD, and within 32,000 
flight hours after the TADD is replaced, do the general visual 
inspection for damage, as specified in paragraph (f) of this AD. 
Thereafter, repeat the test and inspection at the repetitive 
intervals specified in Table 1 of this AD, except when the times for 
a hot air leak test and a general visual inspection coincide, the 
leak test is not required.

Optional Terminating Action

    (j) Replacing existing TADDs with new or serviceable, improved 
TADDs terminates repetitive test and inspection requirements as 
specified in paragraphs (j)(1), (j)(2), and (j)(3) of this AD. New 
or serviceable, improved TADDs are those having a part number listed 
in the ``New TADD Part Number'' or ``New Sidewall Riser Duct Assy 
Part Number'' column, as applicable, of the tables in Section 2.C.2. 
of Boeing Service Bulletin 747-21A2418, Revision 3, dated December 
21, 2004; or Revision 4, dated November 17, 2005.
    (1) The repetitive general visual inspections required by 
paragraph (f)(2) of this AD are terminated for each TADD that is 
replaced with a new or serviceable, improved TADD.
    (2) Replacing all TADDs on one side of the airplane with new or 
serviceable, improved TADDs terminates all repetitive tests required 
by paragraph (f)(1) of this AD and all repetitive inspections 
required by paragraph (f)(2) of this AD only for the side of the 
airplane on which the improved TADDs are installed.
    (3) Replacing all TADDs on both sides of the airplane with new 
or serviceable, improved TADDs terminates all repetitive tests 
required by paragraph (f)(1) of this AD and all repetitive 
inspections required by paragraph (f)(2) of this AD.

Previously Accomplished Actions

    (k) Actions done before the effective date of this AD in 
accordance with Boeing Service Bulletin 747-21A2418, dated November 
14, 2002; Revision 1, dated October 16, 2003; Revision 2, dated 
March 4, 2004; or Revision 3, dated December 21, 2004; are 
acceptable for compliance with the corresponding actions required by 
this AD.

Alternative Methods of Compliance (AMOCs)

    (l)(1) The Manager, Seattle Aircraft Certification Office, 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.


[[Page 56070]]


    Issued in Renton, Washington, on September 14, 2006.
Kalene C. Yanamura,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 06-8232 Filed 9-25-06; 8:45 am]
BILLING CODE 4910-13-P