[Federal Register Volume 69, Number 230 (Wednesday, December 1, 2004)]
[Proposed Rules]
[Pages 69844-69847]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-26492]


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

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), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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

SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD) 
for certain Boeing Model 747 airplanes. This proposed AD would require 
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. This proposed AD also would provide an 
optional terminating action for the repetitive tests. This proposed AD 
is prompted by reports of deteriorating sealants both inside and 
outside the center wing fuel tank due to heat damage from leaking 
TADDs. We are proposing 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.

DATES: We must receive comments on this proposed AD by January 18, 
2005.

ADDRESSES: Use one of the following addresses to submit comments on 
this proposed AD.
     DOT Docket Web site: Go to http://dms.dot.gov and follow 
the instructions for sending your comments electronically.
     Government-wide rulemaking Web site: Go to http://www.regulations.gov and follow the instructions for sending your 
comments electronically.
     Mail: Docket Management Facility, U.S. Department of 
Transportation, 400 Seventh Street, SW., Nassif Building, room PL-401, 
Washington, DC 20590.
     By fax: (202) 493-2251.
     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.
    For service information identified in this proposed AD, contact 
Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-
2207.
    You can examine the contents of this AD docket on the Internet at 
http://dms.dot.gov, or at the Docket Management Facility, U.S. 
Department of Transportation, 400 Seventh Street, SW., room PL-401, on 
the plaza level of the Nassif Building, Washington, DC.

FOR FURTHER INFORMATION CONTACT:
    Technical information: Dan Kinney, Aerospace Engineer, Propulsion 
Branch, ANM-140S, FAA, Seattle Aircraft Certification Office, 1601 Lind 
Avenue, SW., Renton, Washington 98055-4056; telephone (425) 917-6499; 
fax (425) 917-6590.
    Plain language information: Marcia Walters, [email protected].

SUPPLEMENTARY INFORMATION:

Docket Management System (DMS)

    The FAA has implemented new procedures for maintaining AD dockets 
electronically. As of May 17, 2004, new AD actions are posted on DMS 
and assigned a docket number. We track each action and assign a 
corresponding directorate identifier. The DMS AD docket number is in 
the form ``Docket No. FAA-2004-99999.'' The Transport Airplane 
Directorate identifier is in the form ``Directorate Identifier 2004-NM-
999-AD.'' Each DMS AD docket also lists the directorate identifier 
(``Old Docket Number'') as a cross-reference for searching purposes.

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 under ADDRESSES. Include ``Docket No. FAA-2004-19755; 
Directorate Identifier 2004-NM-23-AD'' in the subject line 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 submitted 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 can review DOT's complete Privacy Act Statement in the 
Federal Register published on April 11, 2000 (65 FR 19477-78), or you 
can visit http://dms.dot.gov.

[[Page 69845]]

    We are reviewing the writing style we currently use in regulatory 
documents. We are interested in your comments on whether the style of 
this document is clear, and your suggestions to improve the clarity of 
our communications that affect you. You can get more information about 
plain language at http://www.faa.gov/language and http://www.plainlanguage.gov.

Examining the Docket

    You can 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 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 DMS receives them.

Discussion

    We have received a report indicating that inspections have revealed 
deteriorating sealants both inside and outside the center wing fuel 
tank on certain Boeing Model 747 airplanes. The deterioration is 
attributed to damage caused by hot air leaking from the trim air 
diffuser ducts or sidewall riser duct assemblies (collectively referred 
to in this proposed AD as ``TADDs''), which are part of the cabin air 
distribution system that is located between the top of the center wing 
fuel tank and the floor of the passenger cabin. These hot air leaks 
occur when the fiberglass diffuser ducts are damaged by the hot bleed 
air that they carry, leading the fiberglass diffuser ducts to leak or 
disconnect from the titanium trim air manifold. The release of hot air 
can damage the upper skin of the center wing section, the longitudinal 
floor beams, and the fuselage frame intercostals, as well as the 
sealants of the center wing fuel tank. Damage to the sealants inside or 
outside the center wing fuel tank could allow fuel or fuel vapors to 
leak into an area where ignition sources may be present. This 
condition, if not corrected, could result in a fire or explosion.

Relevant Service Information

    We have reviewed Boeing Alert Service Bulletin 747-21A2418, 
Revision 2, dated March 4, 2004; including Information Notice (IN) 747-
21A2418 IN 01, dated March 11, 2004. The service bulletin describes 
procedures for repetitive tests to detect hot air leaking from the 
TADDs, related investigative actions, and corrective actions if 
necessary. The related investigative actions are repetitive general 
visual inspections for discrepancies or damage of the TADDs; and, if 
necessary, for damage of adjacent structure, the primary and secondary 
fuel barriers of the center wing fuel tank, control cables, and cable 
pulleys, and for raised cable seals. The corrective actions, if any 
damage is found, consist of replacing any damaged TADD with a new TADD 
having the same part number, or a new, improved TADD that has a higher 
temperature tolerance; and repairing any damage to adjacent structure, 
the primary and secondary fuel barriers of the center wing fuel tank, 
control cables, cable pulleys, or raised cable seals. After a TADD is 
replaced with a new TADD having the same part number, there is no need 
to test or inspect the replaced TADD until 21,200 flight hours after 
the replacement. After a TADD is replaced with a new, improved TADD, 
the repetitive inspections are no longer needed for that TADD. 
Accomplishing the actions specified in the service information is 
intended to adequately address the unsafe condition.
    IN 747-21A2418 IN 01 identifies some headings that were 
inadvertently omitted from the Accomplishment Instructions of Boeing 
Alert Service Bulletin 747-21A2418, Revision 2. These headings clarify 
what procedures apply to which airplane configuration.
    The service bulletin refers to Chapter 21-61-20 of the 747 Airplane 
Maintenance Manual as an additional source for service information for 
the test and inspection of the TADDs. Chapter 21-61-20 contains, among 
other things, detailed procedures for the general visual inspection of 
the TADDs for damage or discrepancies, including detachment of the trim 
air duct from the diffuser duct, delamination, missing or softened 
surface material, or blackened material. For any discrepant TADD, 
Chapter 21-61-20 also describes procedures for 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.

FAA's Determination and Requirements of the Proposed AD

    We have evaluated all pertinent information and identified an 
unsafe condition that is likely to exist or develop on other airplanes 
of this same type design. Therefore, we are proposing this AD, which 
would require doing the actions specified in the service information 
described previously, except as discussed under ``Differences Between 
the Proposed AD and Service Information.''
    This proposed AD also provides an optional terminating action for 
the repetitive inspections, which is replacing the existing TADDs with 
new, improved TADDs. We have determined that it is acceptable to allow 
you to continue doing repetitive tests and inspections in lieu of 
requiring that you do the terminating action. In making this 
determination, we considered that long-term continued operational 
safety in this case will be adequately ensured by repetitive 
inspections to detect hot air leaking from the TADDs or discrepancies 
of the TADDs before these conditions are a hazard to the airplane.

Clarification of Proposed Requirements

    This proposed AD would require that any replacement TADD must be 
new. Used TADDs are not acceptable replacement parts. Because the 
material of the TADDs deteriorates at a known rate, an operator would 
have to know how many total flight hours had been accumulated on a 
serviceable TADD, and would have to test and inspect that TADD at 
appropriate intervals. We find that it is unlikely that operators will 
have all of the data that would be needed for a serviceable TADD to be 
an acceptable replacement. Therefore, this proposed AD would allow 
replacement only with new parts.

Differences Between the Proposed AD and Service Information

    For the hot air leak test, the service bulletin provides a 
compliance time of the earlier of 180 days or 2,000 flight hours after 
the release date of Revision 2 of the service bulletin, once the 
airplane has accumulated 20,000 total flight hours. For this test, this 
proposed AD would require the initial test to be done prior to the 
accumulation of 21,200 flight hours, or within 1,200 flight hours after 
the effective date of this AD, whichever is later. This compliance time 
is the equivalent of the inspection threshold of 20,000 total flight 
hours, plus a grace period of 1,200 flight hours (which is equivalent 
to one repetitive interval, as specified in the service bulletin). In 
developing an appropriate compliance time for this AD, 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 a 1,200-flight-hour grace period represents an appropriate 
interval of time for affected airplanes (with close to or more than 
20,000 total flight hours as of the effective date of the AD) to 
continue to operate without compromising safety.

[[Page 69846]]

Costs of Compliance

    This proposed AD would affect about 1,305 airplanes worldwide. The 
following table provides the estimated costs for U.S. operators to 
comply with this proposed AD.

                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                           Average                                  Number  of
                                  Work      labor                     Cost per         U.S.-
            Action               hours     rate per     Parts         airplane      registered      Fleet cost
                                             hour                                    airplanes
----------------------------------------------------------------------------------------------------------------
Hot air leak test............          3        $65  None.......  $195 per test             246  $47,970 per
                                                                   cycle.                         test cycle.
General visual inspection....          5         65  None.......  $325 per                  246  $79,950 per
                                                                   inspection                     inspection
                                                                   cycle.                         cycle.
----------------------------------------------------------------------------------------------------------------

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. 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 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 Federal Aviation Administration (FAA) must receive 
comments on this AD action by January 18, 2005.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Boeing Model 747-100, 747-100B, 747-100B 
SUD, 747-200B, 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 was prompted by reports of deteriorating sealants 
both inside and outside the center wing fuel tank due to heat damage 
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 Alert Service Bulletin 747-21A2418, Revision 
2, dated March 4, 2004; including Information Notice 747-21A2418 IN 
01, dated March 11, 2004.

                       Table 1.--Compliance Times
------------------------------------------------------------------------
                                                      Then repeat within
                                                         this interval
        Do this action--           Initially at the     until paragraph
                                      later of--         (j) is done--
 
------------------------------------------------------------------------
(1) Repetitive test to detect     Prior to the        1,200 flight
 hot air leaking from TADDs.       accumulation of     hours.
                                   21,200 total
                                   flight hours, or
                                   within 1,200
                                   flight hours
                                   after the
                                   effective date of
                                   this AD.
(2) General visual inspection     Prior to the        7,000 flight
 for damage or discrepancies of    accumulation of     hours.
 the TADDs.                        27,000 total
                                   flight hours, or
                                   within 7,000
                                   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 Alert Service Bulletin 747-21A2418, Revision 2, 
refers to Chapter 21-61-20 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

[[Page 69847]]

Accomplishment Instructions of Boeing Alert Service Bulletin 747-
21A2418, Revision 2, dated March 4, 2004; including Information 
Notice 747-21A2418 IN 01, dated March 11, 2004.

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: 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; do 
applicable repairs; and replace the damaged TADD with a new TADD 
having the same part number or a new, 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. Do all of these actions 
in accordance with the Accomplishment Instructions of Boeing Alert 
Service Bulletin 747-21A2418, Revision 2, dated March 4, 2004; 
including Information Notice 747-21A2418 IN 01, dated March 11, 
2004. Then, 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.

    Note 3: Only new TADDs, not used ones, are acceptable as 
replacement parts, as specified in paragraph (h) of this AD.

    (i) For any TADD, whether damaged or not, 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 27,000 
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.

Optional Terminating Action

    (j) For any TADD that is replaced with a new, 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 Boeing Alert Service Bulletin 747-
21A2418, Revision 2, dated March 4, 2004; including Information 
Notice 747-21A2418 IN 01, dated March 11, 2004: The repetitive tests 
and inspections required by this AD are terminated for the TADD that 
is replaced with a new, improved TADD.

Previously Accomplished Actions

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

Alternative Methods of Compliance (AMOCs)

    (l) The Manager, Seattle Aircraft Certification Office (ACO), 
FAA, has the authority to approve AMOCs for this AD, if requested in 
accordance with the procedures found in 14 CFR 39.19.

    Issued in Renton, Washington, on November 17, 2004.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 04-26492 Filed 11-30-04; 8:45 am]
BILLING CODE 4910-13-P